Improvements relating to time-of-flight mass analyser

Abstract

The invention relates to an assembly comprising a vacuum chamber and a time-of-flight mass spectrometer, wherein the time-of-flight mass spectrometer is housed within the vacuum chamber. The time-of-flight mass spectrometer comprises a first electrode and a second electrode spaced apart a distance therebetween defining a portion of an ion flight path. The assembly further comprises a first support for supporting the first electrode, the first support being arranged between an inner surface of the vacuum chamber and the first electrode. The first support is configured to allow relative movement between at least a portion of the inner surface of the vacuum chamber and the first electrode. The inner surface of the vacuum chamber and the first electrode are thermally coupled. The invention further relates to a multi-reflecting time-of-flight mass analyzer. The invention further relates to an apparatus for degassing by heating and subsequently cooling a surface within a vacuum chamber to remove contaminants from the surface.

Description

TECHNICAL FIELD

[0001] The present invention relates to improving baking efficiency, improving thermal compensation and reducing stress and friction on components of a time-of-flight mass analyser. BACKGROUND

[0002] In time-of-flight (TOF) mass spectrometry, the time of flight of an ion is measured to determine the mass-to-charge ratio (m / z). It is well known that the time of flight of an ion is proportional to the square root of its mass-to-charge ratio. The recorded detection time is related to the m / z ratio by a calibration function. The ambient temperature of a mass spectrometer can vary by more than 10 degrees during use, resulting in thermal expansion of mechanical parts and thermal induced drift of electronic components (voltage supply). Temperature variations of a TOF-MS result in a change of the measured time of flight of a given species of ion and thus a drift of the measured m / z of the ion.

[0003] Several approaches have been employed in the past to minimise these effects. For example, as discussed in US 10593525 B2, the mass calibration can be updated frequently so that drift is reasonably accounted for by using known analytes or comparison with a second, more stable analyser. Alternatively, the system can be temperature controlled to reduce drift. However, this adds cost and engineering complexity. As another example, in US-B-6,700,118, several sensors are employed to obtain temperature and strain measurements from the instrument. The measured parameters are then used in conjunction with a mathematical model to provide an adjusted mass spectrum.

[0004] US 6998607 B1 relates to a thermal compensation scheme in a time-of-flight mass analyser, wherein the analyser is constructed such that, although materials can be allowed to expand / contract with temperature, their actual ion flight path lengths remain approximately the same. This is achieved by using spacers attached to the detector which, upon thermal expansion, reduce the distance between the ion source and the detector so as to reduce the flight path length between the ion source and the detector. This reduction in flight path compensates for an increase in flight path through other components of the analyser. However, due to this arrangement, friction between the spacers and the detector can impede smooth expansion / contraction.

[0005] Furthermore, it is noted that, since the flight path length of multi-reflecting time-of-flight mass analysers is much longer, it is difficult to apply known thermal compensation methods to these multi-reflecting time-of-flight mass analysers.

[0006] Their long flight path lengths require excellent vacuum conditions, typically at least an order of magnitude lower pressure than conventional analyzers. This requires therefore baking the vacuum chamber housing the analyzer to perform outgassing. Baking is heating the vacuum chamber to 80 to 120 °C for about 4 to 24 hours. Outgassing is the removal of contaminants from the inner surfaces of the vacuum chamber that occurs during baking. To enable the analyzer to be used after baking, the analyzer needs to be cooled down. However, efficient heating / cooling requires good thermal coupling between the analyzer and the vacuum chamber. In known arrangements, good thermal coupling requires the inner surfaces of the vacuum chamber and the analyzer to be firmly fixed together. The forces from thermal expansion / contraction of the vacuum chamber are then therefore transmitted to the analyzer, stressing the components of the analyzer and destroying the effect of the thermal compensation methods employed.

[0007] The present invention seeks to address some of the problems of prior art arrangements. SUMMARY

[0008] In a first aspect of the present invention, there is provided an assembly comprising a vacuum chamber and a time-of-flight mass spectrometer, wherein the time-of-flight mass spectrometer is housed within the vacuum chamber,

[0009] The time-of-flight mass spectrometer comprises a first electrode and a second electrode, the second electrode being spaced apart from the first electrode by a distance defining a portion of an ion flight path therebetween;

[0010] The assembly further comprises a first support for supporting the first electrode, the first support being arranged between the inner surface of the vacuum chamber and the first electrode;

[0011] wherein the first support allows relative movement between at least a portion of the inner surface of the vacuum chamber and the first electrode;

[0012] wherein the inner surface of the vacuum chamber and the first electrode are thermally coupled.

[0013] The assembly enables the first support to be thermally coupled to the vacuum chamber whilst also enabling the first support to move relative to the vacuum chamber.

[0014] During baking, the vacuum chamber is heated to remove contaminants from the inner surfaces of the vacuum chamber. To enable the analyzer to be used after baking, the analyzer needs to be cooled down. The first aspect of the present invention thermally couples the vacuum chamber and the first electrode of the analyzer to enable efficient heating / cooling during baking. However, as the first support enables the inner surface of the vacuum chamber to move relative to the first electrode, the vacuum chamber can expand / contract without exerting forces on the electrodes, reducing stress and friction on the components of the analyzer, in particular the electrodes. It also prevents thermal expansion / contraction of the vacuum chamber from significantly affecting the thermal compensation scheme for the analyzer.

[0015] The vacuum chamber comprises or defines a cavity therein which houses the time-of-flight mass spectrometer.

[0016] The inner surface of the vacuum chamber can be any internal surface formed by the walls of the vacuum chamber.

[0017] The analyser can comprise an ion source and an ion detector. The total ion flight path is from the ion source to the ion detector (via the first and second ion optical mirrors).

[0018] The first support can be connected to the inner surface of the vacuum chamber. The first support can be directly connected to the inner surface of the vacuum chamber and / or directly connected to the first electrode.

[0019] Preferably, the assembly can comprise a second support for supporting the second electrode. The second support can have a similar configuration to the first support. The second support is arranged between the inner surface of the vacuum chamber and the second electrode, wherein the second support allows relative movement between at least a portion of the inner surface of the vacuum chamber and the second electrode.

[0020] The second support can be connected to the inner surface of the vacuum chamber. The second support can be directly connected to the inner surface of the vacuum chamber and / or directly connected to the second electrode.

[0021] Preferably, the first and / or second support comprises a surface configured to support the respective electrode thereon, wherein the surface is electrically insulating. The respective electrode can be directly supported on the surface of the support. The first and / or second support can be coated with an electrically insulating material or can be formed entirely of an electrically insulating material to provide the electrically insulating surface.

[0022] The first and / or second support allows relative translation of the respective electrode relative to at least a portion of the inner surface of the vacuum chamber. (I.e. the above-mentioned relative movement can be relative translation). The relative translation can be in any direction.

[0023] In one embodiment, the first and / or second support comprises one or more rotatable elements, each rotatable element having a curved surface configured to support the respective electrode thereon. The curved surface can be electrically insulating. Rotation of the one or more rotatable elements can effect relative translation between the electrode and the inner surface of the vacuum chamber. The curved surface can be in direct contact with the respective electrode but not in direct contact with the inner surface of the vacuum chamber. Alternatively, the curved surface can be in direct contact with both the respective electrode and the inner surface of the vacuum chamber. For example, each support can comprise a plurality of rotatable elements spaced apart along a longitudinal direction of the respective electrode.

[0024] Each rotatable element can be a ball, wherein the ball is received by a holder such that the ball can rotate relative to the holder, and wherein the holder is coupled to the inner surface of the vacuum chamber. The holder can be formed of a flexible material or shaped to impart flexibility. The holder can be mounted directly to the inner surface of the vacuum chamber. The holder can flexibly hold the position of the respective ball. The holder can limit the translation of the respective ball.

[0025] Preferably, the inner surface of the vacuum chamber comprises a complementary recess for receiving each rotatable element. The complementary recess can receive the ball and / or the holder of the rotatable element.

[0026] In an alternative arrangement, each rotatable element can be a cylinder.

[0027] In one embodiment, the first support and the second support are integrally formed. In other words, the first support and the second support can form a single unified structure.

[0028] The first and / or second support can comprise a lubricating layer that is electrically insulating. The lubricating layer can also be thermally conductive, thereby providing a thermal coupling between the electrode and the inner surface of the vacuum chamber. The lubricating layer can extend between the inner surface of the vacuum chamber and the respective electrode. The first support can be a first portion of the lubricating layer, and the second support can be a second portion of the lubricating layer. The first and second portions of the lubricating layer can be separate from each other. Alternatively, the first and second portions can form a unified lubricating layer, such that the first and second supports are integrally formed. The lubricating layer can comprise a vacuum grease and / or a soft metal, such as an indium foil.

[0029] The first and / or second support can comprise a layer that has a low coefficient of friction and is formed of an electrically insulating material, such as a low-friction plastic / Teflon. The layer can also be thermally conductive. The first support can be a first portion of the layer, and the second support can be a second portion of the layer. The first and second portions of the layer can be separate from each other. Alternatively, the first and second portions can form a unified lubricating layer, such that the first and second supports are integrally formed.

[0030] In one embodiment, the first and / or second support comprises one or more wires configured to suspend the respective electrode from the inner surface of the vacuum chamber. Preferably, in this arrangement, the inner surface of the vacuum chamber is the upper surface of the vacuum chamber. The one or more wires can be formed of a thermally conductive material. The one or more wires can be at least partially covered by an electrically insulating material. The one or more wires can be compressed and / or merged at their ends.

[0031] In one embodiment, the first and / or second support comprises one or more springs extending between the inner surface of the vacuum chamber and the electrode. The one or more springs can be formed of a thermally conductive material. Each spring can extend between a mount connected to the inner surface of the vacuum chamber and a mount connected to a surface of the respective electrode. Alternatively, each spring can extend directly between the inner surface of the vacuum chamber and a surface of the respective electrode.

[0032] Preferably, the inner surface of the vacuum chamber and the second electrode are thermally coupled. The thermal coupling between the inner surface of the vacuum chamber and the second electrode can be achieved by the same or different features as used to provide thermal coupling between the inner surface of the vacuum chamber and the first electrode.

[0033] In one embodiment, the thermal coupling between the inner surface of the vacuum chamber and one or both of the first and / or second electrode can be achieved by one or more flexible heat conductors. The flexible heat conductors enable relative movement between the inner surface of the vacuum chamber and the respective electrode. Preferably, each flexible heat conductor is connected between the inner surface of the vacuum chamber and the respective electrode.

[0034] Preferably, each flexible heat conductor comprises one or more thermally conductive wires. The plurality of thermally conductive wires can be assembled together, for example woven together, to form a flexible strip. At least a portion of the one or more thermally conductive wires can be covered by an electrically insulating material.

[0035] Preferably, each flexible heat conductor comprises a first mount configured to connect the flexible heat conductor to the respective electrode and a second mount configured to connect the flexible heat conductor to the inner surface of the vacuum chamber.

[0036] The first and second mounts can be directly connected to the inner surface of the vacuum chamber and the respective electrode. Alternatively, a spacer can be provided between the first mount and the respective electrode and / or between the second mount and the inner surface of the vacuum chamber.

[0037] The first mount can be electrically insulated from the respective electrode. For example, a surface of the first mount that comes into contact with the respective electrode can be formed of an electrically insulating material. Alternatively, a spacer can be positioned between the first mount and the respective electrode, the spacer being configured to space the first mount apart from the respective electrode, wherein the spacer is formed of an electrically insulating material or has a surface coating formed of an electrically insulating material. The first mount can be bolted to the respective electrode. The bolt can be surrounded by an electrically insulating material.

[0038] Preferably, the first and / or second support is thermally conductive, thereby thermally coupling the inner surface of the vacuum chamber to the respective electrode. The first and / or second support can be formed of a thermally conductive material, such as a ceramic. In this arrangement, the flexible heat conductors can not be required.

[0039] Liquid cooling that can be directly temperature controlled can be used to thermally couple the inner surface of the vacuum chamber to the electrodes. For liquid cooling, a conduit, such as a flexible sealed tube, can be provided with a coolant flowing therethrough to thermally couple the electrodes and the inner surface of the vacuum chamber. The conduit can be connected between the inner surface of the vacuum chamber and the electrodes. A pump can be provided to circulate the coolant, such as a cooling liquid, through the internal volume of the conduit so that the coolant flows between the inner surface of the vacuum chamber and the electrodes via the conduit, thereby effectively transferring heat therebetween.

[0040] Flexible bellows that can be directly temperature controlled can be used to thermally couple the inner surface of the vacuum chamber to the electrodes. For example, the electrodes can be mounted to flexible bellows that are connected to a port of the vacuum chamber rather than the inner surface of the vacuum chamber. The flexible bellows can be directly air cooled for temperature control.

[0041] The first electrode can be one of a first plurality of electrodes, and the second electrode can be one of a second plurality of electrodes, wherein the first plurality of electrodes is spaced apart from the second plurality of electrodes defining a portion of the ion flight path therebetween.

[0042] One or more of the electrodes of the first plurality of electrodes can be supported by a support configured similarly to the first support. In other words, one or more of the electrodes of the first plurality of electrodes can be supported by a respective support that allows relative movement between at least a portion of the inner surface of the vacuum chamber and the respective electrode.

[0043] One or more of the electrodes of the second plurality of electrodes can be supported by a support configured similarly to the second support. In other words, one or more of the electrodes of the second plurality of electrodes can be supported by a respective support that allows relative movement between at least a portion of the inner surface of the vacuum chamber and the respective electrode.

[0044] Preferably, the time-of-flight mass spectrometer is a multi-reflecting time-of-flight mass spectrometer, the multi-reflecting time-of-flight mass analyser comprising a first ion optical mirror comprising at least the first electrode and a second ion optical mirror comprising at least the second electrode, the second ion optical mirror being spaced apart from the first ion optical mirror by a distance defining at least a portion of the ion flight path therebetween.

[0045] The first ion optical mirror can comprise a first plurality of electrodes spaced apart from one another, and / or the second ion optical mirror can comprise a second plurality of electrodes spaced apart from one another. In this arrangement, the first electrode is the electrode of the first plurality of electrodes that is furthest from the second plurality of electrodes, and the second electrode is the electrode of the second plurality of electrodes that is furthest from the first plurality of electrodes.

[0046] The supports for one or more of the electrodes of the first and second plurality of electrodes can be employed similarly to the first and second supports.

[0047] Alternatively, the time-of-flight mass spectrometer can be a multi-turn time-of-flight mass spectrometer, the multi-turn time-of-flight mass analyzer comprising a first electrostatic sector comprising at least a first electrode and a second electrostatic sector comprising at least a second electrode, the second electrostatic sector being spaced apart from the first electrostatic sector by a distance defining at least a portion of an ion flight path therebetween. The multi-turn time-of-flight mass spectrometer can further comprise a further pair of electrostatic sectors configured similarly to the first and second electrostatic sectors. For example, the multi-turn time-of-flight mass spectrometer can comprise third and fourth electrostatic sectors configured similarly to the first and second electrostatic sectors, wherein the fourth electrostatic sector is spaced apart from the third electrostatic sector by a distance defining a portion of the ion flight path therebetween. The ions can oscillate along the flight path between the first, second, third and fourth electrostatic sectors.

[0048] The first electrostatic sector can comprise a first plurality of electrodes spaced apart from one another, and / or the second electrostatic sector can comprise a second plurality of electrodes spaced apart from one another.

[0049] The support for one or more of the electrodes in the first and second plurality of electrodes can be employed similarly to the first and second supports.

[0050] The ion source and detector are preferably mounted to the inner surface of the vacuum chamber. In a less preferred arrangement, the detector can optionally be mounted to an ion optical mirror or electrostatic sector proximate the detector, but such an arrangement requires a flexible electrical connection therebetween.

[0051] In one preferred embodiment, a thermal compensation scheme is employed. The first electrode has a per Kelvin m / z ratio shift and the second electrode has a per Kelvin m / z ratio shift, the assembly further comprising a connector connected to the first electrode at a first connection point and to the second electrode at a second connection point, wherein the connector has a per Kelvin m / z ratio shift, the connector defining a first length between the first and second connection points at a reference temperature, wherein the first length, the locations of the first and second connection points, and the material of the connector are selected to compensate for the sum of the per Kelvin m / z ratio shifts in the first and second electrodes.

[0052] Thermally coupling the electrodes to the vacuum chamber but supporting the electrodes so that the electrodes can move relative to the vacuum chamber, while also employing the thermal compensation scheme enables effective heating / cooling during baking without compromising the accuracy of the analysis or putting stress or friction on components of the analyzer.

[0053] The thermal compensation scheme is particularly advantageous for multi-reflecting time-of-flight mass analyzers.

[0054] As discussed in the background section, it is noted that known thermal compensation methods are difficult to apply to these multi-reflecting time-of-flight mass analyzers due to the much longer flight path lengths of multi-reflecting time-of-flight mass analyzers. In multi-reflecting time-of-flight mass analyzers, the majority of the change in ion flight path with temperature occurs due to thermal expansion / contraction of the spaced apart electrodes.

[0055] The described thermal compensation scheme enables effective thermal compensation in multi-reflecting time-of-flight mass analyzers without causing significant friction between components.

[0056] Thus, in a second aspect of the invention, there is provided a multi-reflecting time-of-flight mass analyzer comprising the above described thermal compensation scheme. More specifically, there is provided a multi-reflecting time-of-flight mass analyzer comprising:

[0057] a first ion optical mirror comprising a first electrode having a per Kelvin m / z ratio shift,

[0058] a second ion optical mirror comprising a second electrode having a per Kelvin m / z ratio shift, wherein the second ion optical mirror is spaced apart from the first ion optical mirror by a distance defining a portion of an ion flight path therebetween;

[0059] a connector connected to the first electrode at a first connection point and to the second electrode at a second connection point, wherein the connector has a per Kelvin m / z ratio shift, the connector defining a first length between the first and second connection points at a reference temperature;

[0060] wherein the first length, the positions of the first and second connection points, and the material of the connector are selected to compensate for the sum of the per Kelvin m / z ratio shifts in the electrodes of the first and second ion optical mirrors.

[0061] Preferably, the first ion optical mirror comprises a first plurality of electrodes and / or wherein the second ion optical mirror comprises a second plurality of electrodes.

[0062] Preferably, the first electrode is the electrode of the first plurality of electrodes furthest from the second ion optical mirror, and / or wherein the second electrode is the electrode of the second plurality of electrodes furthest from the first ion optical mirror.

[0063] The following paragraphs apply to the thermal compensation scheme when employed in the first or second aspect of the invention.

[0064] Temperature changes cause expansion / contraction of the electrodes of the mass analyzer. This in turn causes changes in the length of the flight path within and between the spaced apart electrodes of the mass analyzer. For example, in the absence of the connector in place, the length of a portion of the flight path between the spaced apart electrodes will increase due to thermal expansion of the electrodes.

[0065] As the electrodes expand, the length of the flight path within the electrodes will also increase due to the greater width of the electrodes. These changes in the length of the flight path in turn result in changes in the total flight time, and thus changes in the measured m / z of the ions detected by the mass analyzer. This is referred to as a per Kelvin m / z ratio shift (i.e., Am / z). The changes in the length of the flight path due to expansion of each electrode can be determined based on the coefficient of thermal expansion of the material, its dimensions, and geometry. The flight path length affected by each electrode can also extend beyond its geometric length and into additional field-free regions due to potential sag between the electrodes. The change in the m / z ratio measured for the ions can be determined based on the determined changes in the length of the flight path. It should be appreciated that the relationship between the m / z ratio shift and the temperature perturbation (i.e., per Kelvin m / z ratio shift) can be positive or negative depending on the geometry of the mass analyzer and electrodes.

[0066] In other words, the first electrode has a per Kelvin m / z ratio shift (i.e., the amount of m / z shift caused by a 1 K temperature change) associated with it. For example, the first electrode can have a per Kelvin m / z ratio shift of -0.1 ppm / K. In such a case, a temperature change of +10 K would cause a measured ion mass shift of -1 ppm (parts per million, i.e., 0.0001%). Correspondingly, a temperature change of -10 K would cause a m / z ratio shift of +1 ppm of the measured ions.

[0067] The connector is connected to the first electrode at a first connection point and to the second electrode at a second connection point. The connector cannot translate relative to the electrodes. The first and second connection points can be points on the electrodes to which the connector is coupled (directly or indirectly). The connector can be directly connected to the electrodes by, for example, a bolt or pin or screw or glue. Alternatively, the connector can be indirectly connected to the electrodes. Indirect connection of the connector to the electrodes refers to an arrangement in which the connector and the electrodes are connected via an intervening or intermediate element. The connector can be connected to the electrodes via, for example, one or more clamps and / or mounts. The connector can be configured such that it maintains separation between the first and second electrodes, which in turn maintains separation between the electrodes of the first ion optical mirror and the electrodes of the second ion optical mirror, wherein the mass analyzer is a multi-reflecting mass analyzer. The first connection point is generally fixed on the first electrode and the second connection point is generally fixed on the second electrode. The first connection point is generally a point on the first electrode and the second connection point is generally a point on the second electrode. As noted above, in the absence of the connector in place, thermal expansion of the electrodes would increase the distance between the first and second electrodes. In the presence of the connector in place, the increase in their width due to thermal expansion of the electrodes would cause the proximal edges of the electrodes to come closer to each other, thereby decreasing the distance between the first and second electrodes. However, the thermal expansion of the connector increases the distance between the first and second connection points, thus compensating for the increase in the width of the electrodes, which would otherwise decrease the separation between the first and second electrodes. Thus, the connector substantially maintains the separation between the first and second electrodes.

[0068] The connector can extend above or below the first and / or second electrodes. In other words, the first connection point can be on an upper surface of the first electrode and the second connection point can be on an upper surface of the second electrode. Alternatively, the first connection point can be on a lower surface of the first electrode and the second connection point can be on a lower surface of the second electrode. The connector can optionally extend beyond the outer edges of the first electrode and beyond the outer edges of the second electrode.

[0069] In the presence of the connector in place, the m / z ratio shift per Kelvin of the first electrode depends on the coefficient of thermal expansion of the material forming the first electrode, its dimensions (e.g. length, width and thickness) and the location of the first connection point. As noted above, it will be appreciated that the relationship between the m / z ratio shift and the temperature perturbation (i.e. the m / z ratio shift per Kelvin) can be positive or negative depending on the geometry of the mass analyzer and the first electrode.

[0070] The per Kelvin m / z ratio shift of the second electrode, with the connector in place, depends on the coefficient of thermal expansion of the material forming the second electrode, its dimensions (e.g. length, width and thickness) and the position of the second connection point. As mentioned above, it will be appreciated that the relationship between the m / z ratio shift and the temperature perturbation (i.e. the per Kelvin m / z ratio shift) can be positive or negative depending on the geometry of the mass analyser and the second electrode.

[0071] The per Kelvin m / z ratio shift of the connector depends on the coefficient of thermal expansion of the material forming it, its length between the first and second connection points and the position of the first and second connection points. The length of the connector between the first and second connection points at a reference temperature is referred to as the first length. The reference temperature can be room temperature or any specified temperature. The material of the connector, the length of the connector between the first and second connection points at the reference temperature (the first length) and the position of the first and second connection points are selected so that the per Kelvin m / z ratio shift of the connector can compensate for the per Kelvin m / z ratio shifts of the first and second electrodes.

[0072] By compensation, it is meant that the per Kelvin m / z ratio shift of the connector is opposite to the total per Kelvin m / z ratio shift of the first and second electrodes. That is, the material of the connector, the first length (i.e. the length of the connector between the first and second connection points at the reference temperature) and the position of the first and second connection points are selected so that the overall m / z shift of the electrodes per degree Kelvin is reduced towards zero.

[0073] Preferably, the compensation is such that the sum of the per Kelvin m / z ratio shifts of the connector and the first and second electrodes is less than ±10 ppm / K, preferably less than ±5 ppm / K, more preferably less than ±3 ppm / K, even more preferably less than ±2 ppm / K, most preferably less than ±1 ppm / K.

[0074] In the case where the first electrode is one of a first plurality of electrodes and the second electrode is one of a second plurality of electrodes, the material of the connector, the first length (i.e. the length of the connector between the first and second connection points at the reference temperature) and the position of the first and second connection points can be selected so that the per Kelvin m / z ratio shift of the connector can compensate for the total per Kelvin m / z ratio shift of the first and second plurality of electrodes. For example, the sum of the per Kelvin m / z ratio shifts of the connector and the first and second plurality of electrodes can be less than ±10 ppm / K, preferably less than ±5 ppm / K, more preferably less than ±3 ppm / K, even more preferably less than ±2 ppm / K, most preferably less than ±1 ppm / K.

[0075] When employed in a multiple reflecting mass analyzer, the material of the connector, the first length (i.e., the length of the connector between the first and second connection points at a reference temperature), and the positions of the first and second connection points can be selected such that the per Kelvin m / z ratio shift of the connector can compensate for the per Kelvin m / z ratio shift of some or all of the electrodes of the first and second ion optical mirrors. Preferably, the compensation is such that the sum of the per Kelvin m / z ratio shifts of the connector and some or all of the electrodes of the first and second ion optical mirrors is less than ±10 ppm / K, preferably less than ±5 ppm / K, more preferably less than ±3 ppm / K, even more preferably less than ±2 ppm / K, most preferably less than ±1 ppm / K.

[0076] Preferably, the coefficient of thermal expansion of the connector is less than the coefficient of thermal expansion of the electrodes. For example, the coefficient of thermal expansion of the connector can be < 1 / 2 of the coefficient of thermal expansion of the electrodes, more preferably < 1 / 5 of the coefficient of thermal expansion of the electrodes, most preferably < 1 / 10 of the coefficient of thermal expansion of the electrodes.

[0077] As described above, the material of the connector, the first length (i.e., the length of the connector between the first and second connection points at a reference temperature), and the positions of the first and second connection points are selected to compensate for at least the per Kelvin m / z ratio shift of the electrodes. While the majority of the per Kelvin m / z ratio shift of the analyzer can be attributed to the electrodes, it should be noted that the material of the connector, the first length (i.e., the length of the connector between the first and second connection points at a reference temperature), and the positions of the first and second connection points can also be selected to compensate for the per Kelvin m / z ratio shift of some or all of the components of the analyzer (e.g., ion source, detector, spacers, etc.).

[0078] For example, the analyzer can also include an ion source and a detector, with a total ion flight path between the ion source and the detector, the ion source and the detector can each have a per Kelvin m / z ratio shift. The material of the connector, the first length (i.e., the length of the connector between the first and second connection points at a reference temperature), and the positions of the first and second connection points can be selected such that the per Kelvin m / z ratio shift of the connector can compensate for the total per Kelvin m / z ratio shift of the electrodes, the ion source, and the detector. For example, the sum of the per Kelvin m / z ratio shifts of the connector, the first and second plurality of electrodes, the ion source, and the detector can be less than ±10 ppm / K, preferably less than ±5 ppm / K, more preferably less than ±3 ppm / K, even more preferably less than ±2 ppm / K, most preferably less than ±1 ppm / K.

[0079] The analyser can further comprise one or more spacers positioned between the electrodes, the spacers being configured to define a spacing between the electrodes, each spacer can have a per Kelvin m / z ratio offset. The material of the connector, the first length (i.e. the length of the connector between the first and second connection points at the reference temperature) and the positions of the first and second connection points can be selected such that the per Kelvin m / z ratio offset of the connector can compensate for the total per Kelvin m / z ratio offset of the electrodes and the spacers. For example, the sum of the per Kelvin m / z ratio offsets of the connector, the first and second plurality of electrodes and the spacers can be less than ±10 ppm / K, preferably less than ±5 ppm / K, more preferably less than ±3 ppm / K, even more preferably less than ±2 ppm / K, most preferably less than ±1 ppm / K.

[0080] The material of the connector, the first length (i.e. the length of the connector between the first and second connection points at the reference temperature) and the positions of the first and second connection points can be selected such that the per Kelvin m / z ratio offset of the connector can compensate for the total per Kelvin m / z ratio offset of the electrodes, the ion source, the detector and the spacers. For example, the sum of the per Kelvin m / z ratio offsets of the connector, the first and second plurality of electrodes, the ion source, the detector and the spacers can be less than ±10 ppm / K, preferably less than ±5 ppm / K, more preferably less than ±3 ppm / K, even more preferably less than ±2 ppm / K, most preferably less than ±1 ppm / K.

[0081] The compensation can be such that the total flight time (i.e. the time it takes for an ion to travel from the ion source to the detector along the total ion flight path) remains substantially constant.

[0082] Preferably, the connector extends at least transverse to the longitudinal direction of the first electrode. More preferably, the connector extends substantially perpendicular to the longitudinal direction of the first electrode. Alternatively, the connector can extend substantially perpendicular to an axis bisecting the angle between the first and second ion optical mirrors. Thus, the length of the connector can extend substantially parallel to the direction in which the first and second electrodes are spaced apart (i.e. substantially parallel to the flight path between the first and second electrodes).

[0083] Preferably, the connector is rod-like, which can have any cross-sectional shape, such as square, circular, etc. Alternatively, the connector can be shaped as a planar strip / band.

[0084] Preferably, the connector is a first connector, wherein the analyser further comprises a second connector, the second connector being connected to the first electrode at a third connection point and to the second electrode at a fourth connection point, wherein the second connector defines a second length between the third and fourth connection points at the reference temperature, wherein the second connector is spaced apart from the first connector, preferably wherein the second connector is parallel to the first connector.

[0085] The second connector can be configured similarly to the first connector, and the above description of the first connector applies equally to the second connector.

[0086] As discussed in further detail below, in a multi-reflecting time-of-flight mass analyzer, the electrodes of the first ion optical mirror can be tilted with respect to the electrodes of the second ion optical mirror. The tilt angle (i.e. the angle between the longitudinal direction of the first electrodes and the longitudinal direction of the second electrodes) can preferably be 0 to 5 degrees, more preferably 0 to 2 degrees.

[0087] Preferably, the second length, the positions of the third and fourth connection points, and the material of the second connector are chosen such that the angle between the first and second electrodes remains within ±0.01°, preferably ±0.001° after thermal expansion of the electrodes and the connectors.

[0088] By employing two connectors spaced apart from each other and appropriately choosing the material of the second connector, the positions of the connection points, and the length of the connector between the connection points, the tilt angle between the electrodes of the first ion optical mirror and the electrodes of the second ion optical mirror can be substantially maintained regardless of thermal expansion / contraction of the electrodes and the connectors without the electrodes being bent.

[0089] Preferably, the second connector is spaced apart from the first connector in the longitudinal direction of the first electrodes.

[0090] When the electrodes are elongated / contracted due to thermal expansion / contraction along their longitudinal direction, the first connector can move relative to the second connector such that the spacing between the first and second connectors is adjusted.

[0091] Preferably, the second connector is attached to the first connector only via the first and second electrodes. In other words, there can be no direct connection between the first and second electrodes. Thus, the connectors do not constrain the expansion / contraction of the electrodes along their longitudinal direction, and thus the electrodes are not bent upon thermal expansion / contraction.

[0092] To prevent the electrode assembly from drifting out of position, the second connector can preferably be attached to the inner surface of the vacuum chamber at a fixed position between the third and fourth connection points. The second connector can be bolted / pinned / glued to the vacuum chamber at the fixed position. Even though the drift of the electrode assembly as a whole in the vacuum chamber is prevented, the first connector can still move relative to the second connector such that the connectors do not limit the elongation of the electrodes upon thermal expansion.

[0093] The assembly of the first aspect of the invention can also include one or more cooling channels arranged to cool the surface within the vacuum chamber by delivering a cooling medium through the one or more cooling channels; a heater arranged to heat the surface within the vacuum chamber; and an insulating material surrounding an outer surface of the vacuum chamber.

[0094] By providing an insulating material surrounding an outer surface of the vacuum chamber, a heater configured to heat a surface within the vacuum chamber, and cooling channels arranged to cool the surface of the vacuum chamber when provided with a cooling medium, the vacuum chamber can be efficiently heated during baking and subsequently cooled. As mentioned above, during baking, the inner surface of the vacuum chamber is heated to remove contaminants therefrom. After heating, the vacuum chamber needs to be cooled before use of the mass analyser therein. For efficiency, mass analysers of importance are baked within a reasonable time frame. The combination of insulating material, heater and cooling channels configured as mentioned above is capable of efficiently heating and cooling a vacuum chamber housing a mass analyser.

[0095] The arrangement to improve thermal efficiency can be employed with the features of the first and second aspects of the invention. The arrangement for efficient heating and cooling is also provided as a third aspect of the invention.

[0096] Thus, in the third aspect of the invention, there is provided an apparatus for outgassing to remove contaminants from a surface by heating and subsequently cooling the surface within a vacuum chamber, the apparatus comprising:

[0097] a vacuum chamber for housing a mass analyser;

[0098] a heater arranged to heat the surface within the vacuum chamber;

[0099] one or more cooling channels arranged to cool the surface within the vacuum chamber by delivering a cooling medium through the one or more channels; and

[0100] an insulating material surrounding an outer surface of the vacuum chamber.

[0101] The following paragraphs apply to the thermal efficiency arrangement when employed in the first, second or third aspects of the invention.

[0102] Outgassing refers to the process of removing contaminants from the inner surface of the vacuum chamber. It typically occurs during baking, where the vacuum chamber is heated at 80 to 120 °C for 4 to 24 hours. Subsequent cooling of the vacuum chamber is then required for use of the analyser housed therein.

[0103] The surface heated by the heater and cooled by the cooling medium within the cooling channels is the inner surface of the vacuum chamber.

[0104] The insulation material preferably surrounds the entire outer surface of the vacuum chamber. The insulation material is preferably a foam, such as a polyurethane or polypropylene foam.

[0105] The heater is preferably located between the insulation material and the outer surface of the vacuum chamber. Alternatively, the heater can be positioned outside the insulation material, but can comprise one or more conduits arranged to direct hot air into the cavity formed within the vacuum chamber via an opening in the wall of the vacuum chamber. Alternatively, the heater can be positioned inside the vacuum chamber (i.e. within the cavity formed by the vacuum chamber).

[0106] The cooling medium received by the one or more cooling channels can be a gas or a liquid, preferably the cooling medium is air.

[0107] The mass analyser can be a time-of-flight mass analyser. Preferably, the mass analyser is a multi-reflecting time-of-flight mass analyser of the second aspect described above.

[0108] The one or more cooling channels can extend around and / or through the vacuum chamber. Preferably, the one or more cooling channels can extend at least partially through the vacuum chamber and / or at least partially around the outer surface of the vacuum chamber. For example, the one or more cooling channels can extend around the outer periphery of the vacuum chamber.

[0109] Preferably, the cooling channels are within the insulation material. In other words, preferably the cooling channels are covered by and / or at least partially housed within the insulation material.

[0110] Optionally, the one or more cooling channels extend between an inlet and an outlet. The inlet and outlet can be apertures / through-holes formed in one or more walls of the vacuum chamber. Alternatively, the inlet and outlet can be formed as recesses and / or grooves formed in the edges of the walls of the vacuum chamber.

[0111] The one or more cooling channels can be formed by a tube. Preferably, the tube can extend between an inlet and an outlet formed as apertures in one or more walls of the vacuum chamber.

[0112] In preferred embodiments, each cooling channel can be formed as a recess within a wall of the vacuum chamber, preferably wherein each cooling channel is formed as a recess in an outer wall of the vacuum chamber, more preferably wherein the recess formed in the outer wall of the vacuum chamber is covered by the insulation material. The recess can extend along at least a portion of the outer wall of the vacuum chamber. Alternatively, each cooling channel can be formed within an inner surface of the insulation material.

[0113] Preferably, the one or more cooling channels are configured to actively cool the surfaces within the vacuum chamber during use. For example, at least one of the one or more cooling channels can comprise one or more fans configured to drive a cooling medium through the respective cooling channel. Alternatively / additionally, the one or more cooling channels can comprise one or more pumps configured to drive a cooling medium through the respective cooling channel. Typically, the flow of cooling medium through the cooling channels can be restricted except when the fans and / or pumps are activated.

[0114] Preferably, the one or more cooling channels can comprise one or more heat sinks and / or heat exchangers configured to receive the cooling medium flowing through the cooling channels during use.

[0115] The assembly / apparatus can further comprise a controller configured to control the activation and deactivation of the heater and / or the one or more fans, preferably wherein the controller is configured to activate the one or more fans after the heater is deactivated. Thus, in use during baking, the controller activates the heater such that the heater heats the surfaces within the vacuum chamber. Due to the use of insulating material around the outer surface of the vacuum chamber, the efficiency of heating the surfaces within the vacuum chamber is improved. Once the contaminants have been removed from the surfaces within the vacuum chamber, the controller deactivates the heater and activates the one or more fans / pumps such that a cooling medium is driven through the one or more cooling channels, thereby actively cooling the surfaces within the vacuum chamber. Thus, this improves the efficiency of cooling the surfaces within the vacuum chamber, such that the time taken for baking is reduced.

[0116] A method of performing degassing to remove contaminants from surfaces within a vacuum chamber using an apparatus comprising: a vacuum chamber for receiving a mass analyser; a heater arranged to heat the surfaces within the vacuum chamber; one or more cooling channels arranged to cool the surfaces within the vacuum chamber by transporting a cooling medium through the one or more channels, the one or more cooling channels comprising one or more fans and / or pumps configured to drive the cooling medium through the one or more cooling channels; and insulating material around an outer surface of the vacuum chamber; the method comprising:

[0117] activating the heater to heat the surfaces within the vacuum chamber at 80 to 120 K for 4 to 24 hours;

[0118] deactivating the heater;

[0119] activating the one or more fans and / or pumps to drive the cooling medium through the cooling channels for 4 to 12 hours. BRIEF DESCRIPTION OF DRAWINGS

[0120] The application can be practiced in several ways, and some embodiments will now be described by way of example only and with reference to the accompanying drawings in which:

[0121] Figure 1 A schematic illustration of a plan view of an assembly according to the first aspect of the application is shown when viewed from below.

[0122] Figure 2 A schematic illustration of an end view of a portion of an assembly according to the first aspect of the application is shown, the assembly comprising first and second supports supporting first and second electrodes respectively, the assembly further comprising a flexible heat conductor thermally coupling the electrodes to an inner surface of a vacuum chamber.

[0123] Figure 3 A schematic illustration of a support that can be used in an assembly according to the first aspect of the application is shown.

[0124] Figure 4(a) shows a schematic illustration of an end view of a portion of an assembly according to the first aspect of the application.

[0125] Figure 4(b) shows a schematic illustration of a perspective view of a flexible heat conductor that can be used in an assembly according to the first aspect of the application.

[0126] Figure 5 A schematic illustration of a plan view of a portion of an assembly according to the second aspect of the application is shown when viewed from below.

[0127] Figure 6 A schematic illustration of an end view of a portion of an assembly according to the second aspect of the application is shown.

[0128] Figure 7 A schematic illustration of a plan view of a portion of an assembly according to the first and second aspects of the application is shown when viewed from below.

[0129] Figure 8 A schematic illustration of a plan view of a portion of an apparatus according to the third aspect of the application is shown when viewed from above, with the mass analyser removed from view for clarity.

[0130] Figure 9 is a graph demonstrating the m / z ratio shift in ppm measured as a function of temperature change in Kelvin for an arrangement according to the first, second and third aspects of the application.

[0131] Figure 10 is a graph demonstrating the efficiency of the vacuum chamber and mass analyser of an assembly heating and cooling Figure 9 during baking.

[0132] Figure 11 is a schematic illustration of a perspective view of a portion of an assembly according to the second aspect of the application. Detailed Implementation

[0133] Figure 1 This is a schematic plan view of an assembly 10 according to a first aspect of the invention, comprising a vacuum chamber 20 and a time-of-flight mass analyzer 30, wherein the time-of-flight mass analyzer is a multiple reflection time-of-flight mass analyzer (MR-TOF). While the use of MR-TOF mass analyzers has certain advantages, the inventive concept of the first aspect of the invention described and claimed is equally applicable to any form of time-of-flight mass analyzer, such as a multi-turn mass analyzer, and the claims will be interpreted accordingly. It can also be applied to other types of mass analyzers, such as Fourier transform mass analyzers and electrostatic orbital trap mass analyzers, for example, in which ions oscillate in a quadro logarithmic potential.

[0134] The MR-TOF 30 is housed / retained within a vacuum chamber 20. The MR-TOF includes an electrode arrangement forming first and second opposing ion optical mirrors 50 and 60, which are spaced apart from each other along a distance defining a portion of an ion flight path. The first ion optical mirror 50 includes a first plurality of electrodes 51, and the second ion optical mirror 60 includes a second plurality of electrodes 61. The first electrode 51a is the electrode farthest from the second ion optical mirror 60 among the first plurality of electrodes 51. The second electrode 61a is the electrode farthest from the first ion optical mirror 50 among the second plurality of electrodes 61.

[0135] Electrodes 51 and 61 are elongated in their longitudinal direction. The longitudinal direction can be defined as the direction generally aligned with the longitudinal axis of electrodes 51 and 61. The transverse direction of electrodes 51 and 61 is transverse (across), preferably perpendicular to the longitudinal direction of electrodes 51 and 61. The first plurality of electrodes 51 and the second plurality of electrodes 61 are spaced apart from each other in a direction transverse to the longitudinal direction of electrodes 51 and 61.

[0136] The first plurality of electrodes 51 (i.e. the electrodes of the first ion optical mirror 50) are tilted with respect to the second plurality of electrodes 61 (i.e. the electrodes of the second ion optical mirror 60) as described in US9136101, creating a potential gradient which retards the drift velocity of the ions and causes them to reflect back and focus onto the detector 70 in the drift dimension (the drift dimension is substantially aligned with the longitudinal dimension of the electrodes 51, 61). The tilt of the opposing mirrors typically has the negative side effect of changing the time period of the ion oscillation as the ions travel down the drift dimension, making it difficult to achieve good ion time focusing. This is corrected by the fringe electrodes 80 which change the flight potential of a portion of the inter-mirror space, varying down the length of the electrodes of the first and second ion optical mirrors 50, 60. Such correction or compensation electrodes 80 are also described in US9136101. The combination of the varying width of the fringe electrodes 80 and the varying spacing between the first and second ion optical mirrors 50, 60 allows for the reflection and spatial focusing of the ions onto the detector 70, as well as maintaining good time focusing.

[0137] In use, the ion source 90, such as an ion trap with pulsed ion ejection, injects ions into the first plurality of electrodes 51 of the first ion optical mirror 50, and the ions then oscillate between the first and second ion optical mirrors 50, 60. The ejection angle of the ions from the ion source 90 and additional deflector 100, 110 allows control of the ion energy in the drift direction, such that the ions are directed down the length of the electrodes 51, 61 of the first and second ion optical mirrors 50, 60 as they oscillate, creating a zigzag trajectory. The total ion flight path is from the ion source 90 to the detector 70.

[0138] Figure 2 An end view of the electrodes 51 of the first ion optical mirror 50 and a portion of the inner surface of the vacuum chamber 20 is depicted. In this preferred arrangement, the inner surface 21 of the vacuum chamber 20 is the bottom surface of the vacuum chamber 20 (i.e. the floor of the vacuum chamber).

[0139] As Figure 2 best shown, some of the first plurality of electrodes 51a, 51b, 51c, 51d are supported by a support 120 arranged between the inner surface 21 of the vacuum chamber 20 and the respective electrodes 51, 61. The support 120 allows for relative movement between at least a portion of the inner surface 21 of the vacuum chamber 20 and the respective electrodes 51. In Figure 2In the preferred embodiment depicted, the support comprises a ball 121 held in place by a flexible retainer 122. The retainer 122 can limit lateral translation of the ball 121 received therein. The retainer 122 can be formed of a flexible material or can be shaped to impart flexibility. The retainer 122 can be formed of a sheet of metal that is laser cut and then folded. The retainer can alternatively be formed of Teflon. The ball 121 can rotate, thereby enabling relative movement between the respective electrode 51, 61 it supports and the inner surface 21 of the vacuum chamber 20. For example, the ball 121 enables the respective electrode 51, 61 it supports to translate in its longitudinal direction and in its lateral direction relative to the inner surface 21 of the vacuum chamber 20.

[0140] In Figure 2 In the preferred embodiment depicted, the retainer 122 has an opening 123 configured to receive the ball 121 therein. In Figure 2 In the preferred arrangement shown, the inner surface 21 of the vacuum chamber comprises a recess 21a that receives the ball 121 therein. The retainer 122 preferably extends across the recess 21a formed in the inner surface 21 of the vacuum chamber 20, such that the retainer contacts and / or is fixed to the inner surface 21 of the vacuum chamber 20 on either side of the recess 21a. The retainer 122 can be generally planar. As noted above, the flexibility of the retainer 122 (due to being formed of a flexible material or being shaped to impart flexibility) can enable the retainer 122 to flex laterally to allow the ball 121 to translate laterally, albeit limitedly, by rotation.

[0141] Figure 3 A schematic view showing an alternative configuration of the retainer 122 of the support 120 is shown. In Figure 3 In the optional arrangement shown, the retainer 122 has an opening 123 configured to receive the ball 121 therein. The retainer comprises a generally planar element 124 that defines the opening, and comprises one or more flexible protrusions 124a that extend into the opening 123, the flexible protrusions being configured to flexibly retain the ball 121. The protrusions 124a can be arranged radially and / or can extend around the ball. The retainer further comprises one or more lateral flanges 125 that extend from the generally planar element 124, for affixing the retainer 122 to the inner surface 21 of the vacuum chamber 20. The one or more flanges 125 can be affixed to the inner surface 21 of the vacuum chamber 20 within the recess 21a or on either side of the recess 21a.

[0142] The ball 121 is preferably formed of or coated with an electrically insulating material, such as ceramic, such that the ball 121 is electrically insulated from the electrode it supports. The retainer 122 can be formed of, for example, a metallic material.

[0143] Similar supports 120 can be used for the second plurality of electrodes 61, which are not shown in Figure 2 detail.

[0144] As Figure 1 best illustrated in Figure 1 is a plan view of the assembly when viewed from below (in which the holders 122 of the support 120 and the inner surface 21 of the vacuum chamber 20 are not shown), one or more of the first and second plurality of electrodes 51, 61 can comprise a plurality of balls 121 that act as the support 120. For example, a first ball 121 can be positioned proximate to a first end of the electrodes 51, 61 and spaced apart from a second ball 121 positioned proximate to a second end of the electrodes 51, 61 along a longitudinal direction of the electrodes 51, 61. In this preferred arrangement, the electrode 51a of the first ion optical mirror 50 farthest from the second ion optical mirror 60 (i.e. the first electrode 51a) and the electrode 51e of the first ion optical mirror proximate to the second ion optical mirror 60 are supported by one or more of the above-mentioned supports 120. Similarly, the electrode 61a of the second ion optical mirror 60 farthest from the first ion optical mirror 50 (i.e. the second electrode 61a) and the electrode 61e of the second ion optical mirror 60 proximate to the first ion optical mirror 50 are supported by one or more of the above-mentioned supports 120.

[0145] As Figure 2 best illustrated, the electrodes of the first plurality of electrodes 51 can be mounted on a first pair of mounting rods 130, which can be formed from a ceramic material. The electrodes of the first plurality of electrodes 51 can comprise holes and / or slots of appropriate tolerance configured to receive the mounting rods 130 such that the contact surfaces of the mounting rods 130 with the electrodes 51, 61 mounted thereon are limited. Such an arrangement reduces friction between the electrodes 51, 61 and the mounting rods 130. In an optional alternative arrangement, the mounting rods 130 are formed from anodised aluminium rods, preferably coated with an electrically insulating material. Such an arrangement can result in reduced friction between the electrodes 51, 61 and the mounting rods 130. However, the mounting rods 130 are preferably formed from a ceramic material. Each electrode of the first plurality of electrodes 51 is spaced apart from an adjacent electrode of the first plurality of electrodes by a spacer 140 therebetween. The spacers 140 are referred to herein as electrode spacers 140. The electrode spacers 140 are preferably formed from an electrically insulating material, such as ceramic. An end stop 131 is preferably provided at each end of each mounting rod 130 to retain the electrodes 51 on the mounting rods 130. A resilient element 132, such as a spring, can also be mounted on the mounting rod between the end stops. The resilient element 132 can be biased to maintain contact between each of the electrodes 51 and their adjacent spacers 140. Expansion or contraction of the electrodes 51 and / or movement of the electrodes 51 along an axis parallel to the mounting rods 130 can be accommodated by expansion or contraction of the resilient element 132. Similar arrangements can be used for the second plurality of electrodes 61, which are not shown in Figure 2 .

[0146] InFigure 1 In the illustrated embodiment, each of the electrodes of the first and second plurality of electrodes 51, 61 is preferably thermally coupled to the inner surface 21 of the vacuum chamber 20 by a respective flexible heat conductor 150. The flexible heat conductor 150 is best shown in Figures 4(a) and (b). Figure 4(a) depicts an end view of a portion of the assembly of Figure 1 and 2 includes one of the first plurality of electrodes 51 (first electrode 51a), a flexible heat conductor 150 and a portion of the inner surface 21 of the vacuum chamber 20. Figure 4(b) depicts a perspective view of the flexible heat conductor 150. The term "flexible" in relation to the flexible heat conductor 150 refers to the ability of the flexible heat conductor 150 to bend / move without breaking in normal use, such that the flexible heat conductor 150 does not impede movement of the electrodes 51, 61 relative to the inner surface 21 of the vacuum chamber 20.

[0147] Each flexible heat conductor 150 can include a plurality of wires. The plurality of wires can be woven together to form a flexible ribbon 151. Preferably, at least the upper surface of the plurality of wires is covered with an electrically insulating material, such as Teflon, which has been found to prevent voltage breakdown without significantly affecting the vacuum quality. The plurality of wires can be completely surrounded by an electrically insulating material, such as Teflon. The one or more wires can be compressed and / or merged at their ends.

[0148] Each flexible heat conductor can include a first mount 152 configured to connect the flexible heat conductor 150 to the respective electrode 51, 61 and a second mount 153 configured to connect the flexible heat conductor to the inner surface 21 of the vacuum chamber 20. The heat conducting wires 151 can extend between the first mount 152 and the second mount 153. The one or more wires can be compressed and / or merged into the first and / or second mounts 152, 153 at their ends. For example, the first and second mounts 152, 153 can be formed from compressed and / or merged wires. The first mount 152 and the second mount 153 are typically formed from a thermally conductive material, such as copper. The first mount 152 is preferably electrically insulated from the respective electrode 51, 61. In this arrangement, the first mount 152 is electrically insulated from the respective electrode 51, 61 by a spacer 155 arranged between the first mount 152 and the respective electrode 51, 61. The spacer 155 is referred to herein as an insulating spacer 155 and is preferably formed from an electrically insulating but thermally conductive material, such as ceramic. Aluminium nitride can be a preferred material for the insulating spacer 155 as it has high thermal conductivity in addition to being electrically insulating.

[0149] The flexible heat conductor 150 can be connected to the respective electrode 51, 61 by using a bolt / screw 156 extending through an opening 152a in the first mount 152 and through an opening (not shown) in the respective electrode 51, 61. The openings are preferably threaded. As shown in Fig. 4(a), at least a portion of the bolt 156 received within the opening 152a in the first mount 152 can be surrounded by an electrically insulating layer 157 to electrically insulate the bolt 156 from the flexible heat conductor 150. The electrically insulating layer 157 can also optionally be thermally conductive.

[0150] The electrically insulating spacers 155 between the first mount 152 of the flexible heat conductor 150 and the respective electrode 51, 61 and the electrically insulating layer 157 surrounding the bolt 156 prevent voltage breakdown that would otherwise occur due to electrical contact between the conducting wires of the flexible heat conductor 150 and the respective electrode 51, 61.

[0151] The second mount 153 can be connected to the inner surface of the vacuum chamber using a bolt / screw 158 extending through an opening 153a in the second mount and a corresponding opening (not shown) in the inner surface 21 of the vacuum chamber 20.

[0152] As Figure 1 is best shown, preferably, the flexible heat conductor 150 is connected proximate to each end of the respective electrode 51, 61, such that each electrode 51, 61 is thermally connected to the inner surface 21 of the vacuum chamber 20 by two thermally flexible heat conductors 150 spaced apart along the longitudinal direction of the electrode 51, 61. Preferably, the flexible heat conductor 150 has a selected cross-section to be able to thermally couple sufficiently to the electrode for efficient heating and cooling of the electrode 51, 61 during baking. Preferably, the flexible heat conductor 150 has a cross-sectional area of 20 to 400 mm 2 , which enables efficient heat transfer between the electrode 51, 61 and the inner surface 21 of the vacuum chamber 20.

[0153] Figure 5 An arrangement according to the second aspect of the present application is depicted that can be employed in a mr-TOF analyzer of Figure 1 .

[0154] The second aspect of the present application provides a thermal compensation scheme.

[0155] The electrodes of the second aspect of the application are configured similarly to the electrode arrangement described in relation to the first aspect of the application. As described above, the electrodes 51, 61 form first and second opposing ion optical mirrors 50, 60 which are spaced apart from each other along a distance which defines a portion of an ion flight path therebetween. The first ion optical mirror 50 comprises a first plurality of electrodes 51 and the second ion optical mirror 60 comprises a second plurality of electrodes 61. The first electrode 51a is the electrode of the first plurality of electrodes 51 which is furthest from the second ion optical mirror 60. The second electrode 61a is the electrode of the second plurality of electrodes 61 which is furthest from the first ion optical mirror 50.

[0156] The electrodes 51, 61 are elongate in their longitudinal direction. The longitudinal direction can be defined as the direction generally aligned with the longitudinal axis of the electrodes 51, 61. The lateral direction of the electrodes is transverse (across), preferably perpendicular, to the longitudinal direction. The first plurality of electrodes 51 and the second plurality of electrodes 61 are spaced apart from each other along a direction transverse to the longitudinal direction of the electrodes 51, 61.

[0157] The first connector 160 is connected to the first electrode 51a at a first connection point 161 and to the second electrode 61a at a second connection point 162. The first connector 160 is fixed to the first and second electrodes 51a, 61a at the first and second connection points 161, 162 such that the first connector 160 cannot translate relative to the electrodes 51a, 61a. The first connector 160 defines a first length between the first connection point 161 and the second connection point 162 at a reference temperature (which can be room temperature). The first connector 160 maintains separation between the first and second electrodes 51a, 61a, which in turn maintains separation / spacing between the first and second ion optical mirrors 50, 60. The first connection point 161 and the second connection point 162 are fixed points on the electrodes 51a, 61a at which the first connector 160 is fixed to the electrodes 51a, 61a. The first connector 160 has corresponding points on it that correspond to the first and second connection points 161, 162 on the electrodes 51a, 61a. In this preferred arrangement, the first connector 160 is arranged beneath the first and second electrodes, and the first and second connection points 161, 162 are arranged on the lower surfaces of the electrodes 51a, 61a. The first connector 160 is preferably connected to the first and second electrodes at the first and second connection points using locating pins that are received within corresponding openings in the electrodes. Alternatively, in an optional arrangement, the first connector 160 can be connected to the first and second electrodes at the first and second connection points using bolts or clamps. Although the first and second connection points 161, 162 are shown as being on the lower surfaces of the first and second electrodes 51a, 61a respectively, they can also be provided on the outer edges of the respective electrodes 51a, 61a. For example, the first connection point 161 can be on the outer edge of the first electrode 51a (i.e. on an edge of the first electrode 51a that extends away from the second electrode 61a in the longitudinal direction of the first electrode 51a). Similarly, the second connection point 162 can be on the outer edge of the second electrode 61a (i.e. on an edge of the second electrode 61a that extends away from the first electrode 51a in the longitudinal direction of the second electrode 61a). In such arrangements, the connector 160 can be indirectly coupled to the first and second electrodes 51a, 61a such as by one or more clamps and / or mounts. For example, as Figure 11As shown, the connector 160 can be indirectly coupled to the first electrode 51a using a connecting pin 300 having a first end 301 clamped by an electrode clamp 310 fixed to the outer edge of the first electrode 51a and a second end 302 received and clamped in a through-hole 163 formed in the first end 164 of the connector 160. The first end 164 of the connector 160 is proximate to the first electrode 51a. The electrode clamp 310 can be formed of complementary first and second portions 310a, 310b. The first portion 310a can be fixed to the outer edge of the first electrode 51a, for example, with an adhesive, and the second portion can be coupled to the first portion using one or more fasteners (referred to herein as first fasteners 311, such as screws / bolts). The first and second portions 310a, 310b can be configured to receive the connecting pin 300 therebetween when assembled together. As Figure 11 As shown, the fastening of the first fasteners 311 can clamp the connecting pin 300 between the first and second portions 310a, 310b of the electrode clamp 310. As Figure 11 As shown, the through-hole 163 is configured to receive the connecting pin 300 therein and has an adjustable diameter. The diameter of the through-hole 163 can be reduced during assembly to clamp the connecting pin 300 within the through-hole 163. The diameter of the through-hole 163 can be adjusted by changing the width of a slot 165 formed in the connector 160, where the slot 165 intersects the through-hole 163. The width of the slot 165 can be adjusted by one or more fasteners (referred to herein as second fasteners 321) that bridge (i.e., extend across) the slot 165. The fastening of the second fasteners 321 can reduce the width of the slot 163 and thus the diameter of the through-hole 163, thereby clamping the connecting pin 300 in the through-hole 163. In Figure 11 In the particular embodiment shown, the first fasteners 311 are a pair of screws and the second fasteners 321 are a single screw. As Figure 11 As shown, the first fasteners 311 can exert a clamping force on the first end 301 of the connecting pin 300 that is perpendicular to a clamping force exerted by the second fasteners 312 (when fastened) on the second end 302 of the connecting pin 300. In Figure 11 In the arrangement shown, the first connection point 161 is a point on the outer edge of the electrode 51a proximate to the electrode clamp 310. As Figure 11As shown, the electrode clamp 310 is on the outer edge of the first electrode 51a. This is advantageous because the electrode clamp 310 will be easy to tighten with a wrench compared to an arrangement where the means for connecting the first electrode 51a and the first connector 160 are positioned on the lower surface of the first electrode 51a. It is also preferred to use a clamp and / or a mount to fix the first connector to the first electrode 51a due to ease of assembly compared to positioning pins and corresponding openings in the first electrode 51a. Furthermore, movement / play of the positioning pins within the openings can cause undesired friction between the positioning pins and the first electrode 51a. Another electrode clamp 310, a connecting pin 300 and a slot formed in the second end of the connector 160 close to the second electrode 61a can be used similarly to connect the connector 160 to the second electrode 61a.

[0158] The first connector 160 has a longitudinal direction extending transversely (i.e. not parallel) to the longitudinal direction of the electrodes 51, 61 such that the connector extends across the space between the first and second ion optical mirrors 50, 60. The longitudinal direction of the first connector 160 is arranged to be substantially perpendicular to the longitudinal direction of the electrodes 51 of the first ion optical mirror 50. By substantially perpendicular is meant an angle of about 90°. The angle between the longitudinal direction of the electrodes 61 of the second ion optical mirror 60 and the first connector 160 is less than 90°, preferably 85 to 89.99°, more preferably 89.90 to 89.98°. In this arrangement, the first connector 160 is shaped as a rod having a circular cross-section.

[0159] In Figure 5 In the preferred arrangement shown, the electrode arrangement further comprises a second connector 170 spaced apart from the first connector 160 and connected to the first electrode 51a at a third connection point 171 and to the second electrode 61a at a fourth connection point 172. The second connector 170 is substantially parallel to the first connector 160. The second connector 170 is spaced apart from the first connector 160 along the longitudinal direction of the electrodes 51, 61. The second connector 170 is configured similarly to the first connector 160 as described above.

[0160] The third connection point 171 is preferably aligned with the first connection point 161 along the longitudinal axis of the first electrode 51a. The fourth connection point 172 is preferably aligned with the second connection point 162 along the longitudinal axis of the second electrode 61a.

[0161] As described above, the temperature change causes expansion / contraction of the electrodes 51, 61 of the mass analyzer. This in turn causes a change in the length of the flight path within and between the spaced apart electrodes 51, 61 of the mass analyzer. For example, in the absence of the connectors 160, 170, when the electrodes expand, the flight path within the electrodes 51, 61 will increase due to the greater width of the electrodes 51, 61 and the greater distance between the first and second ion optical mirrors 50, 60. This change in flight path length in turn causes a change in the total flight time of the ions, and thus a change in the m / z ratio of the ions detected by the mass analyzer (i.e., a per Kelvin m / z ratio shift).

[0162] However, in the presence of the connectors 160, 170, this per Kelvin m / z ratio shift is compensated. Indeed, in the presence of the connectors 160, 170, the increase in the width of the electrodes 51, 61 due to thermal expansion of the electrodes 51, 61 will cause the proximal edges of the spaced apart electrodes 51, 61 to approach each other, thereby reducing the distance between the first and second ion optical mirrors 50, 60. However, the thermal expansion of the connectors 160, 170 increases the distance between the first and second connection points 161, 612 (and the third and fourth connection points 171, 172) to compensate for the increase in the width of the electrodes 51, 61, which would otherwise reduce the spacing between the first and second ion optical mirrors 50, 60. Thus, the connectors 160, 170 substantially maintain the spacing between the first and second ion optical mirrors 50, 60.

[0163] Thus, each electrode 51, 61 has a per Kelvin m / z ratio shift that can be determined based on the coefficient of thermal expansion of the material from which it is formed, its dimensions, geometry, and its respective connection points 161, 162, 171, 172.

[0164] The material of the first and second connectors 160, 170, the positions of the first, second, third, and fourth connection points 161, 162, 171, 172, the length defined by the first connector 160 between the first and second connection points 161, 162 at the reference temperature (i.e., the first length), and the length defined by the second connector 170 between the third and fourth connection points 171, 172 at the reference temperature (i.e., the second length) are selected such that the per Kelvin m / z ratio shift of the connectors 160, 170 can compensate for the per Kelvin m / z ratio shift of all of the electrodes of the first and second plurality of electrodes 51, 61, preferably.

[0165] The compensation can be such that the sum of the per Kelvin m / z ratio shifts of the connectors 160, 170 and of all of the electrodes 51, 61 of the first and second pluralities of electrodes is less than ±10 ppm / K, preferably less than ±5 ppm / K, more preferably less than ±3 ppm / K, even more preferably less than ±2 ppm / K, most preferably less than ±1 ppm.

[0166] Taking into account the geometry of the connectors 160, 170 and of the electrodes 51, 61 (i.e. when the longitudinal direction of the connectors 160, 170 extends parallel to the spacing between the first and second pluralities of electrodes 51, 61 but extends transversely to the longitudinal direction of the electrodes 51, 61), the connectors 160, 170 are formed of a material having a lower coefficient of thermal expansion than the material used to form the electrodes 51, 61, so as to provide thermal compensation. The coefficient of thermal expansion of the connectors 160, 170 can be < 1 / 2 of the coefficient of thermal expansion of the electrodes 51, 61, more preferably < 1 / 5 of the coefficient of thermal expansion of the electrodes 51, 61, most preferably < 1 / 10 of the coefficient of thermal expansion of the electrodes 51, 61.

[0167] Preferably, the connectors 160, 170 are formed of Invar, having a coefficient of thermal expansion of about 1 to 2 ppm / K, preferably 1.2 ppm / K, and / or the electrodes are formed of aluminium, having a coefficient of thermal expansion of about 20 to 30 ppm / K, preferably 25 ppm / K.

[0168] While most of the compensation can be achieved by taking into account only the per Kelvin m / z ratio shifts of the electrodes of the first and second pluralities of electrodes 51, 61. The material of the connectors 160, 170, the positions of the first, second, third and fourth connection points 161, 162, 171, 172, the length (first length) defined by the first connector 160 between the first and second connection points 161, 162 at the reference temperature and the length (second length) defined by the second connector 170 between the third and fourth connection points 171, 172 at the reference temperature can be selected to compensate for the per Kelvin m / z ratio shifts of other components of the analyser other than the electrodes (e.g. the ion source 90, the detector 70 and / or the spacers 140 between the electrodes (inter-electrode spacers 140), etc.). All of these components will expand / contract with temperature changes, resulting in a change in the ion flight path therethrough and consequent changes in the m / z shifts measured for the ions. Each of these components therefore has an associated per Kelvin m / z ratio shift which can be determined based on the coefficient of thermal expansion of the material from which they are formed, their geometry and dimensions.

[0169] For example, the materials of the first and second connectors 160, 170, the positions of the first, second, third and fourth connection points 161, 162, 171, 172, the length of the first connector 160 between the first and second connection points 161, 162 at the reference temperature and the length of the second connector 170 between the third and fourth connection points 171, 172 at the reference temperature can be selected such that the m / z ratio offset per Kelvin of the connectors 160, 170 can compensate for the m / z ratio offset per Kelvin of all of the electrodes of the first and second pluralities of electrodes 51, 61 and the electrode spacers 140.

[0170] The compensation can be such that the sum of the m / z ratio offset per Kelvin of the connectors 160, 170, all of the electrodes of the first and second pluralities of electrodes 51, 61 and the electrode spacers 140 is less than ±10 ppm / K, preferably less than ±5 ppm / K, more preferably less than ±3 ppm / K, even more preferably less than ±2 ppm / K, most preferably less than ±1 ppm / K.

[0171] As another example, the materials of the first and second connectors 160, 170, the positions of the first, second, third and fourth connection points 161, 162, 171, 172, the length of the first connector 160 between the first and second connection points 161, 162 at the reference temperature and the length of the second connector 170 between the third and fourth connection points 171, 172 at the reference temperature can be selected such that the m / z ratio offset per Kelvin of the connectors 160, 170 can compensate for the m / z ratio offset per Kelvin of all of the electrodes of the first and second pluralities of electrodes 51, 61, the electrode spacers 140 and the ion source 90 and the detector 70.

[0172] The compensation can be such that the sum of the m / z ratio offset per Kelvin of the connectors 160, 170, all of the electrodes of the first and second pluralities of electrodes 51, 61 and the electrode spacers 140 is less than ±10 ppm / K, preferably less than ±5 ppm / K, more preferably less than ±3 ppm / K, even more preferably less than ±2 ppm / K, most preferably less than ±1 ppm.

[0173] As mentioned above, the first plurality of electrodes 51 is tilted with respect to the second plurality of electrodes 61. The tilt angle in this arrangement can be about 0.02 to 0.1°. The length defined by the second connector 170 between the third and fourth connection points 171, 172, the positions of the third and fourth connection points 171, 172, and the material of the second connector 170 can be selected so that the tilt angle is maintained as the temperature changes. Preferably, the second connector 170 is formed of the same material as the first connector 160. The length of the second connector 170 between the third and fourth connection points 171, 172 at a reference temperature (i.e., the second length) is different from the length of the first connector 160 between the first and second connection points 161, 162 at the reference temperature (i.e., the first length) to accommodate the tilt angle between the first and second pluralities of electrodes 51, 61. For example, upon a change in temperature, the first and second connectors 160, 170, when formed of the same material, will expand / contract proportionally to each other, thereby maintaining the tilt angle between the first and second pluralities of electrodes 51, 61. After thermal expansion of the electrodes 51, 61 and the connectors 160, 170, the tilt angle is preferably maintained to within ±0.01°, most preferably within ±0.001°. As shown in FIG. 3, in an arrangement in which the first and second connectors 160, 170 are each clamped to the outer edges of the respective electrodes 51, 61, the tilt angle can be obtained by inserting a spacer (not shown) between the electrode clamp 310 (specifically, the first portion 310a of the electrode clamp 310) and the outer edge of the respective electrode 51, 61, which is referred to herein as a tilt spacer. The thickness of the tilt spacer can be selected to obtain the desired tilt angle. The tilt spacer can be, for example, a metal shim. Figure 11

[0174] The second connector 170 is preferably attached to the first connector 160 only via the first and second electrodes 51a, 61a. In other words, preferably there is no direct connection between the first and second connectors 160, 170. Thus, when the electrodes 51, 61 thermally expand in their longitudinal direction, the spacing between the first and second connectors 160, 170 increases to accommodate the expansion, thereby preventing the electrodes 51, 61 from buckling.

[0175] ​The second connector 170 can be fixed to the inner surface of the vacuum chamber at a position between the third and fourth connection points 171, 172, preferably equidistantly between the third and fourth connection points 171, 172. In this preferred arrangement, the second connector 170 is fixed to the inner surface 21 of the vacuum chamber 20 with minimal contact at the fixing point 180. For example, the second connector 170 can be fixed to the inner surface 21 of the vacuum chamber 20 by a positioning pin received in a corresponding opening in the inner surface 21 of the vacuum chamber 20. As another example, a clamp can be used to fix the second connector 170 to the inner surface 21 of the vacuum chamber at the fixing point 180. The clamp can be bolted to the inner surface 21 of the vacuum chamber 20. By using a clamp, the second connector 170 can be fixed to the inner surface 21 of the vacuum chamber 20 without creating a hole or slot in the second connector 170 that would weaken the connector 170. The clamp can also allow for a more rigid connection between the second connector 170 and the inner surface 21 of the vacuum chamber 20. The clamp and the second connector 170 can be made of the same material, which can avoid / reduce stresses or friction that can be generated due to different thermal expansions / contractions of the clamp and the second connector 170. As an example, the second connector 170 and the clamp used to fix the second connector 170 to the inner surface 21 of the vacuum chamber at the fixing point 180 can be formed of invar, which has a thermal expansion coefficient of approximately 1 to 2 ppm / K, preferably 1.2 ppm / K. The inner surface 21 is preferably a bottom surface of the vacuum chamber 20. The first connector 160 can move relative to the second connector 170 due to the expansion of the electrodes 51, 61 along their longitudinal direction, but since the second connector 170 is connected to the inner surface 21 of the vacuum chamber 20 at the fixing point 180, the drift of the electrode assembly as a whole within the vacuum chamber 20 is prevented.

[0176] The connectors 160, 170 are preferably received within a groove (recess or channel) (not shown) formed within the inner surface 21 of the vacuum chamber 20, which is preferably a lower surface of the vacuum chamber. The groove can extend along the portion of the inner surface 21 of the vacuum chamber 20 below the electrodes 51, 61, such that the connectors 160, 170 do not contact the inner surface 21 of the vacuum chamber 20 except at and / or around the fixing point 180, such that the fixing point 180 is not within the groove. Thus, the connectors 160, 170 can not support the electrodes 51, 61. As Figure 11As shown, one or more flexible supports 350 may be provided around at least a portion of the outer surface of each of the connectors 160, 170 to prevent direct contact between the outer surface of each of the connectors 160, 170 and the trench during assembly (i.e., before the connectors 160, 170 are attached to the respective electrodes 51, 61). The flexible supports 350 may be configured to support the respective connectors 160, 170 during assembly prior to their connection to the respective electrodes 51, 61. The flexible supports are formed of or shaped to impart flexibility such that they allow and / or do not impede the thermal expansion or contraction of the connectors 160, 170. The flexible supports may be formed from laser-cut and then folded metal sheets, such as folded aluminum sheets. The flexible supports 350 may extend around the entire periphery of the respective connectors 160, 170, or around a portion of the periphery of the respective connectors 160, 170, which would otherwise contact the trench during assembly prior to their connection to the electrodes 51, 61. Figure 6 As best illustrated, connectors 160 and 170 can be connected to electrodes 51 and 61 via a spacer 190 disposed therebetween, referred to herein as connector spacer 190, such that connectors 160 and 170 are spaced apart from electrodes 51 and 61. Connector spacer 190 can be formed of an electrically insulating material, such as ceramic, such that connector spacer 190 is electrically insulated from the respective electrodes 51 and 61. Alternatively, connectors 160 and 170 can be directly connected to electrodes 51 and 61.

[0177] like Figure 6 As shown, in the second aspect of the invention, the electrodes of the first plurality of electrodes 51 can be mounted on a first pair of mounting rods 130, which can be formed of a ceramic material. This arrangement has been discussed with respect to the first aspect of the invention, and it is equally applicable to the first and second plurality of electrodes 51, 61 of the second aspect of the invention.

[0178] The features of the first and second aspects of this invention can be combined. For example, Figure 7 It shows that it can be used Figure 1 The diagram shows a plan view of the assembly used in MR-TOF, viewed from below. The assembly includes first and second ion optical mirrors 50 and 60 as described in the first and second aspects, a support 120 and a flexible heat conductor 150 as described in the first aspect, and connectors 160 and 170 as described in the second aspect.

[0179] exist Figure 7In the arrangement, the electrodes are thermally coupled to the inner surface 21 of the vacuum chamber 20 by the flexible heat conductor 150 for efficient heat transfer during baking. This improves the efficiency of the degassing process during baking and reduces the time taken to cool the analyser after heating to make it ready for use. The support 120 supporting the electrodes 51, 61 enables relative movement between the inner surface of the vacuum chamber 20 and the electrodes 51, 61. Thus, the stress and friction on the electrodes 51, 61 due to thermal expansion / contraction of the vacuum chamber 20 during baking due to heating and cooling of the vacuum chamber 20 is minimised. In effect, both the electrodes 51, 61 and the inner surface 21 of the vacuum chamber 20 are free to expand / contract with temperature changes without compromising the thermal efficiency between the inner surface 21 of the vacuum chamber 20 and the electrodes 51, 61.

[0180] Furthermore, since the support 120 allows relative movement between the inner surface 21 of the vacuum chamber 20 and the electrodes 51, 61, the thermal expansion / contraction of the vacuum chamber 20 does not significantly affect the thermal compensation scheme described in accordance with the second aspect of the application. In effect, the thermal expansion / contraction of the electrodes 51, 61 and the thermal expansion / contraction of the connectors 160, 170 are not significantly affected by the thermal expansion / contraction of the vacuum chamber 20. This is because the electrodes 51, 61 are supported by the support 120 which allows relative movement between the electrodes 51, 61 and the inner surface 21 of the vacuum chamber 20. The first connector 160 is not directly attached to the vacuum chamber 20. The second connector 170 is only attached to the vacuum chamber 20 by minimal contact (e.g. by a locating pin) at the location (fixed point 180) between the first and second ion optical mirrors 50, 60. Thus, the expansion / contraction of the vacuum chamber 20 when heated and cooled during baking does not cause stress on the electrodes 51, 61 of the analyser.

[0181] As mentioned above, the connectors 160, 170 can be connected to the electrodes 51, 61 via a connector spacer 190 arranged therebetween, such that the connectors are spaced apart from the electrodes 51, 61. The spacer 190 is formed of an electrically insulating material, such as ceramic. The spacer 190 is located at the first, second, third and fourth connection points 161, 162, 171, 172. As mentioned above, the connectors 160, 170 are received within a groove formed in the inner surface 21 of the vacuum chamber 20. The depth of the groove is such that the connectors 160, 170 do not contact the inner surface of the vacuum chamber 20 except at the fixing points 180. Thus, even though the connectors 160, 170 in this arrangement extend below the electrodes 51, 61, the connectors 160, 170 do not support the electrodes 51, 61. Rather, the electrodes 51, 61 can be entirely supported by the support 120, which enables relative movement between the electrodes 51, 61 and the inner surface 21 of the vacuum chamber 20. Thus, the presence of the connectors 160, 170 does not degrade the functionality of the support 120. The flexible heat conductor 150 can have a cross-sectional area of 20 to 400 mm 2 , which enables efficient heat transfer without causing buckling of the connectors 160, 170. One or more flexible heat conductors 150 can be connected between the connectors 160, 170 and the inner surface 21 of the vacuum chamber 20, such that the flexible heat conductors 150 enable heat transfer between the connectors 160, 170 and the inner surface 21 of the vacuum chamber. If the connectors are formed of a material with poor thermal conductivity, such as invar, it can be beneficial to employ a plurality of flexible heat conductors 150 connected to each connector 160, 170.

[0182] Figure 8 is a schematic plan view of a portion of an apparatus 200 for degassing a surface 21 within a vacuum chamber 20 housing a time-of-flight mass analyser 30 by heating and subsequently cooling the surface to remove contaminants from the surface. The apparatus 200 comprises one or more cooling channels 210 arranged to cool the surface within the vacuum chamber 20 by conveying a cooling medium through the cooling channels 210; a heater (not shown) arranged to heat the surface 21 within the vacuum chamber 20; and an insulating material 220 surrounding an outer surface of the vacuum chamber 20.

[0183] The apparatus can be used in a combination of Figure 1 . In other words, Figure 1 The combination of

[0184] As Figure 8The insulating material 220 surrounds most of the outer surface of the vacuum chamber 20, preferably the entire outer surface of the vacuum chamber, as best shown. The insulating material 220 is preferably a foam, such as a polyurethane or polypropylene foam. A heater (not shown) is preferably located between the insulating material 220 and the outer surface of the vacuum chamber 20. The heater can be a heating element which can be attached to the outer surface of the vacuum chamber 20, for example, by screws.

[0185] Figure 8 The illustrated arrangement comprises two cooling channels 210, which are referred to herein as first and second cooling channels 210a, 210b. In this preferred arrangement, each cooling channel 210 is formed as one or more recesses and / or grooves formed in an outer wall of the vacuum chamber 20, preferably in the bottom outer wall of the vacuum chamber. Each cooling channel 210 has a depth which extends through a portion of the thickness of the outer wall of the vacuum chamber 20, such that the cooling channel is formed in the outer surface of the vacuum chamber wall and the inner surface of the vacuum chamber 20 remains intact. The insulating material 220 which surrounds the outer surface of the vacuum chamber 20 also covers the recesses and / or grooves which form the cooling channels 210.

[0186] In Figure 8 In the preferred arrangement, the first cooling channel 210a extends between a first edge 22 of the bottom wall 21 and a second edge 23 of the bottom wall 21, wherein the first and second edges 22, 23 are substantially perpendicular to each other. The second cooling channel 210b extends between a third edge 24 of the bottom wall and the second edge 23 of the bottom wall 21, wherein the third and second edges 24, 23 are perpendicular to each other. In this preferred arrangement, the first and second cooling channels 210a, 210b are curved. By employing curved rather than straight cooling channels 210, the space taken up by the cooling channels 210 is reduced, such that the remaining space can be used more efficiently, for example, for positioning a vacuum pump therein. Alternatively, the first and second cooling channels 210 can extend between the first and third edges 22, 24 or the second and fourth edges 23, 25 of the bottom wall 21, wherein the fourth and second edges 23, 25 are parallel to each other, such that the cooling channels 210 are formed as straight channels. In this preferred arrangement, an inlet 230 of the first cooling channel 210a is formed at the first edge 22 of the bottom wall 21 and an outlet 231 of the first cooling channel 210a is formed at the second edge 23 of the bottom wall 21. An inlet 232 of the second cooling channel 210b is formed at the third edge 24 of the bottom wall 21 and an outlet 233 of the second cooling channel 210b is formed at the second edge 23 of the bottom wall 21.

[0187] The cooling channels 210 can be configured to actively cool the surfaces within the vacuum chamber 20 during use. In this preferred arrangement, the cooling medium employed is a gas, preferably air. Thus, to achieve active cooling, a fan 240 is provided proximate the inlet 230, 232 of each cooling channel 210 to drive the cooling medium through the respective cooling channel 210. In alternative arrangements where a liquid coolant medium is provided, a pump can instead be used to drive the cooling medium through the respective cooling channel 210. Typically, the flow of cooling medium through the cooling channels 210 can be restricted except when the fan 240 and / or pump is activated.

[0188] In this preferred arrangement, a heat sink 250 is provided within each cooling channel 210, preferably downstream of the fan 240. The heat sink 250 is preferably formed from extruded aluminium or copper. The heat sink 250 can be attached to the recess / groove forming each cooling channel 210 by, for example, an adhesive and / or a bolt. The heat sink 250 is preferably formed from extruded aluminium or copper and is configured to receive the cooling medium flowing through the cooling channel 210 during use.

[0189] A vacuum pump is not shown in the arrangement of Figure 8 but can be positioned between the first and second cooling channels 210a, 210b. The vacuum pump can be partially thermally decoupled from the vacuum chamber 20 by a steel plate arranged at the contact surface between the vacuum pump and the vacuum chamber 20.

[0190] The apparatus can also include a controller (not shown) configured to control the activation and deactivation of the heater (not shown) and the activation and deactivation of the fan 240. The controller is configured to activate the fan 240 after the heater is deactivated. Thus, in use, when outgassing is performed to remove contaminants from the surfaces 21 within the vacuum chamber 20 (i.e. during baking), the controller activates the heater such that the heater heats the surfaces 21 within the vacuum chamber 20. Due to the use of the insulating material 220 around the outer surface of the vacuum chamber 20, the efficiency of heating the surfaces within the vacuum chamber 20 is improved. For example, to achieve outgassing for an mr-TOF analyser having a 20m flight path, the heater only requires less than 1KW of power due to the efficiency improvement achieved. Once the contaminants have been removed from the surfaces 21 within the vacuum chamber 20, the controller deactivates the heater and activates the fan 240 such that the cooling medium (in this case air) is driven through the cooling channels 210, thereby actively cooling the surfaces 21 within the vacuum chamber 20. This therefore improves the efficiency of cooling the surfaces 21 within the vacuum chamber 20 such that the time taken for outgassing is reduced.

[0191] The assembly is also advantageous for general use of the time-of-flight mass analyser (i.e. not just during baking (outgassing)). For example, the thermal insulation 220 also protects the mass analyser from temperature variations in the ambient air during use.

[0192] According to Figure 8 The inventive concept described and claimed herein in the third aspect of the invention is equally applicable to any form of mass analyser, and the claims are to be interpreted accordingly.

[0193] The inventive concepts of the first, second and third aspects of the invention described above can be employed together in any combination. For example, the first and third aspects can be employed together, the first and second aspects can be employed together, the second and third aspects can be employed together, or all of the first, second and third aspects can be employed together.

[0194] Experimental data

[0195] The data in Table 1 listed below demonstrates thermal compensation achieved by the following apparatus:

[0196] An assembly employing the second aspect of the invention in which the mass analyser is a mr-TOF analyser. In other words, the assembly comprises an arrangement similar to that shown in Figure 5 and 6 employing a connector 160. In this arrangement, as described above, the analyser comprises a first ion optical mirror 50 comprising a first electrode 51a and a second ion optical mirror 60 comprising a second electrode 61b. The second ion optical mirror 60 is spaced apart from the first ion optical mirror 50 by a distance defining a portion of an ion flight path therebetween. The connector 160 is employed which is connected to the first electrode 51a at a first connection point 161 and to the second electrode at a second connection point 162. The first ion optical mirror 50 comprises a first plurality of electrodes 51 and the second ion optical mirror 60 comprises a second plurality of electrodes 61. The first electrode 51a is the electrode of the first plurality of electrodes 51 furthest from the second plurality of electrodes 61. The second electrode 61a is the electrode of the second plurality of electrodes 61 furthest from the first plurality of electrodes 51. The electrodes of the first plurality of electrodes 51 are spaced apart by a spacing 140 therebetween described above as an electrode spacing 140. The electrodes of the second plurality of electrodes 61 are spaced apart by a spacing 140 therebetween. In the arrangement used to obtain the data in Table 1, the spacing between the first and second ion optical mirrors 50, 60 employed was 8mm.

[0197] The values for the m / z shift per Kelvin listed in the table below were determined based on the simulation analysis of ion trajectories within the analyzer system using the MASIM 3D software. In the table below, the electrodes 51, 61 are labeled M0, M1, M2, M3, M4. As indicated in the table below, the electrodes 51, 61 in the first and second plurality of electrodes have the largest influence on the total m / z shift per Kelvin. The spacers 140 between the electrodes 51, 61 have only a negligible influence on the total m / z shift per Kelvin.

[0198] In this arrangement, a connector 160 is employed which is configured as described above Figure 6 and 7 and which is formed from invar having a length of 632 mm between the first and second connection points. In other words, the connector 160 has a length of 318 mm between its center and the first connection point 161, and the connector has a length of 318 mm between its center and the second connection point 162. The sum of the m / z ratio shift per Kelvin for the electrodes 51, 61, the spacers 140, and the connector 160 is 2.69 ppm / K. Thus, in this arrangement, the compensation achieved by the connector 160 configured as described above Figure 6 and 7 reduces the total m / z ratio shift per Kelvin to 2.69 ppm / K.

[0199]

[0200] It was found that by employing a connector 160 formed from invar and having a length of 678 mm between the first and second connection points, full compensation would be achieved, such that the total m / z ratio shift per Kelvin is reduced to 0. (I.e. a connector 160 is employed in which the connector 160 has a length of 339 mm between its center and the first connection point 161, and the connector 160 has a length of 339 mm between its center and the second connection point 162).

[0201] Figure 9 A measured m / z as a function of temperature is shown for an assembly employing the first, second, and third aspects of the present invention, in which the mass analyzer is a mr-TOF analyzer. In other words, the assembly contains an arrangement similar to that shown in Figure 7 but also contains the features of Figure 8 . In other words, the assembly contains a support 120 and a flexible heat conductor 150 as described according to the first aspect, a connector 160, 170 as described according to the second aspect, and an insulating material 220, a heater, and a cooling channel 210 as described according to the third aspect.

[0202] The mr-TOF mass analyzer has a size of approximately 1 m 2and the total ion flight path length is 21 m. The vacuum chamber 20 is heated with a heating power of 50 W for two 24-hour periods. The m / z of the fluoranthene ions is measured over the 48 hours of the experiment and plotted against its initial value (i.e. before heating). The temperature variation of the vacuum chamber 20 in Kelvin is measured by a PT100 sensor mounted on the vacuum chamber 20. The vacuum chamber 20 reaches a thermal drift of close to +2.5 K and the consequent m / z ratio shift is +3.4 ppm. This therefore corresponds to an m / z ratio shift of 1.4 ppm / K per Kelvin. When the copper heat sink is placed in the cooling channel 210, an abnormal variation of the m / z ratio shift occurs within a few minutes when the heater is started / stopped. This abnormal variation can be considered to reflect stresses on the chamber 20 being transmitted to the ion optical mirrors 50, 60 or movements due to the rapid heating of the electrodes 51, 61. There is also some delay between the m / z shift peak and the vacuum chamber temperature peak due to the time taken for the heat to be transmitted to the electrodes 51, 61 of the ion optical mirrors 50, 60 via the flexible heat conductor 150.

[0203] Figure 10 The performance of heating and cooling the assembly in a cycle typically used for baking (i.e. to perform degassing) is shown. The cycle contains 6 hours of heating followed by continuous forced cooling using the cooling channel 210 with air as the cooling medium flowing therethrough. PT100 sensors are mounted to the vacuum chamber 20 and the four electrodes 51 of the first ion optical mirror 50, referred to as M0 (ground), M1, M2 and M4. In Figure 10 M4 has the highest temperature, followed by M2, then M1, then M0 between 5 and 10 minutes. The vacuum chamber has the lowest temperature. The lines for M1 and M0 overlap at around 10 minutes. It can be seen from this data that the insulating material improves the efficiency of heating the electrodes 51 of the vacuum chamber and the analyser therein and the cooling channel improves the efficiency of cooling the electrodes 51 after heating. The data also shows that the flexible heat conductor 150 provides effective thermal coupling of the electrodes 51 and the vacuum chamber 20. In fact, within 14 hours, the temperature of all the electrodes 51 and the vacuum chamber 20 exceeds 80°C and cools to below 30°C. The final base pressure within the vacuum chamber 20 in which the mr-TOF mass analyser is located is recorded as a respectable 3x10 -9 mbar.

Claims

1. An assembly comprising a vacuum chamber and a time-of-flight mass spectrometer, wherein the time-of-flight mass spectrometer is housed within the vacuum chamber. The time-of-flight mass spectrometer includes a first electrode and a second electrode, the second electrode being spaced apart from the first electrode by a distance defining a portion of the ion flight path; The assembly further includes a first support member for supporting the first electrode, the first support member being disposed between the inner surface of the vacuum chamber and the first electrode. The first support is configured to allow relative movement between at least a portion of the inner surface of the vacuum chamber and the first electrode; The inner surface of the vacuum chamber is thermally coupled to the first electrode. The vacuum chamber is thermally coupled to the first electrode and / or the second electrode via one or more flexible thermal conductors.

2. The assembly of claim 1, wherein the assembly further comprises a second support for supporting the second electrode, the second support being disposed between the inner surface of the vacuum chamber and the second electrode, wherein the second support is configured to allow relative movement between at least a portion of the inner surface of the vacuum chamber and the second electrode.

3. The assembly according to claim 1 or 2, wherein the inner surface of the vacuum chamber and the second electrode are thermally coupled.

4. The assembly of claim 1, wherein each flexible thermal conductor comprises one or more thermally conductive wires.

5. The assembly of claim 4, wherein each flexible thermal conductor includes a first mounting member configured to connect the flexible thermal conductor to a corresponding electrode and a second mounting member configured to connect the flexible thermal conductor to the inner surface of the vacuum chamber.

6. The assembly of claim 5, wherein one or more thermally conductive wires extend between the first mounting member and the second mounting member, wherein the first mounting member and the second mounting member are thermally conductive.

7. The assembly according to claim 5 or 6, wherein the first mounting member is electrically insulated from the corresponding electrode.

8. The assembly according to claim 5 or 6, further comprising a spacer configured to space the first mounting member from the respective electrode.

9. The assembly of claim 8, wherein the spacer is formed of an electrically insulating material.

10. The assembly according to claim 5 or 6, wherein the surface of the first mounting member in contact with the respective electrode is electrically insulated.

11. The assembly of claim 2, wherein the first support and / or the second support is thermally conductive, thereby thermally coupling the inner surface of the vacuum chamber to the respective electrode.

12. The assembly of claim 2, wherein the first support and / or the second support includes a surface configured to support a respective electrode thereon, wherein the surface is electrically insulating.

13. The assembly of claim 2, wherein the first support and / or the second support allows relative translation of the respective electrode with respect to at least a portion of the inner surface of the vacuum chamber.

14. The assembly of claim 13, wherein the first support and / or the second support comprises one or more rotatable elements, each rotatable element having a curved surface configured to support a corresponding electrode thereon.

15. The assembly of claim 14, wherein each rotatable element is a ball, wherein the ball is received by a retainer such that the ball is rotatable relative to the retainer, and wherein the retainer is coupled to the inner surface of the vacuum chamber.

16. The assembly of claim 14 or 15, wherein the inner surface of the vacuum chamber includes complementary recesses for receiving each rotatable element.

17. The assembly of claim 2, wherein the first support and the second support are integrally formed.

18. The assembly of claim 2, wherein the first support and / or the second support comprises a lubricating layer, wherein the lubricating layer is electrically insulating.

19. The assembly of claim 18, wherein the first support is a first portion of the lubricating layer and the second support is a second portion of the lubricating layer.

20. The assembly of claim 19, wherein the first support and the second support are integrally formed.

21. The assembly of claim 2, wherein the first support and / or the second support comprises a layer having a low coefficient of friction and formed of an electrically insulating material.

22. The assembly of claim 21, wherein the first support is a first portion of the layer and the second support is a second portion of the layer.

23. The assembly of claim 22, wherein the first support and the second support are integrally formed.

24. The assembly of claim 2, wherein the first support and / or the second support comprises one or more wires configured to suspend respective electrodes from the inner surface of the vacuum chamber.

25. The assembly of claim 2, wherein the first support and / or the second support comprises one or more springs extending between the inner surface of the vacuum chamber and the electrode.

26. The assembly of claim 1 or 2, wherein the time-of-flight mass spectrometer is a multiple reflection time-of-flight mass spectrometer, the multiple reflection time-of-flight mass analyzer includes a first ion optical mirror and a second ion optical mirror, the first ion optical mirror including at least a first electrode, the second ion optical mirror including at least a second electrode, the second ion optical mirror being spaced apart from the first ion optical mirror by a distance defining at least a portion of the ion flight path.

27. The assembly of claim 26, wherein the first ion optical mirror comprises a first plurality of electrodes spaced apart from each other, and / or wherein the second ion optical mirror comprises a second plurality of electrodes spaced apart from each other.

28. The assembly of claim 1 or 2, wherein the time-of-flight mass spectrometer is a multi-turn time-of-flight mass spectrometer, the multi-turn time-of-flight mass analyzer includes a first electrostatic sector and a second electrostatic sector, the first electrostatic sector including at least the first electrode, the second electrostatic sector including at least the second electrode, the second electrostatic sector being spaced apart from the first electrostatic sector by a distance defining at least a portion of the ion flight path therebetween.

29. The assembly of claim 28, wherein the first electrostatic sector comprises a first plurality of electrodes spaced apart from each other and / or the second electrostatic sector comprises a second plurality of electrodes spaced apart from each other.

30. The assembly of claim 29, wherein the first electrode is the electrode farthest from the second electrostatic sector among the first plurality of electrodes, and / or wherein the second electrode is the electrode farthest from the first electrostatic sector among the second plurality of electrodes.

31. The assembly of claim 27, wherein the first electrode is the electrode farthest from the second ion optical mirror among the first plurality of electrodes, and / or wherein the second electrode is the electrode farthest from the first ion optical mirror among the second plurality of electrodes.

32. The assembly according to claim 1 or 2, wherein the first electrode has an offset per Kelvin m / z, and wherein the second electrode has an offset per Kelvin m / z. The assembly further includes a connector connected to the first electrode at a first connection point and to the second electrode at a second connection point, wherein the connector has an offset per Kelvin m / z ratio and defines a first length between the first connection point and the second connection point at a reference temperature; The first length, the positions of the first connection point and the second connection point, and the material of the connector are selected to compensate for the sum of the offset per Kelvin m / z ratio in the first electrode and the second electrode.

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