IMR-MS Equipment

Abstract

The present invention relates to an apparatus and method for IMR-MS and / or PTR-MS, comprising a sample gas inlet (202, 206), a first ion source (209), a reaction chamber (203), a mass analyser (204), wherein the reaction chamber (203) and the mass analyser (204) are arranged along a central axis (A), characterized in that a second ion source (209) is provided, wherein the sample gas inlet (202, 206) is arranged to introduce gas substantially along the central axis (A) and is connected to the reaction chamber (203); wherein the first ion source (209) and the second ion source (209) are arranged to emit reagent ions substantially perpendicular to the central axis (A); the apparatus further comprises at least one electrode (302, 303, 304, 305) so that the reagent ions emitted from the first or second ion source (209) can be deflected into the reaction chamber (203) substantially in the downstream direction of the central axis (A).

Description

Technical Field

[0001] The present invention relates to a device for ion-molecule-reaction mass spectrometry and / or proton-transfer-reaction mass spectrometry, which comprises a sample gas inlet, a first ion source, a reaction chamber, a mass analyzer, wherein the reaction chamber and the mass analyzer are arranged along a central axis. The present invention also relates to a method for operating the device for ion-molecule-reaction mass spectrometry and / or proton-transfer-reaction mass spectrometry according to the present invention. Background of the Invention

[0003] Ion-molecule-reaction mass spectrometry (IMR-MS) or proton-transfer-reaction mass spectrometry (PTR-MS; both terms are used synonymously throughout this application) is a well-established method for chemical ionization, detection and quantification of (trace) compounds. Details on this technique can be found, for example, in AMEllis, CA Mayhew (Proton Transfer Reaction Mass Spectrometry Principles and Applications, John Wiley & Sons Ltd., UK, 2014). The advantages of this technique are high sensitivity, high selectivity, online quantification, direct sample injection and short response time. Although most common PTR-MS instruments use a ionization reaction from H3O + The technique is by no means limited to this form of ionization. + 、O2 + , Kr + and any other type of positively or negatively charged reagent ions for chemical ionization. In addition to a host of common devices for controlling various voltages, currents, temperatures, vacuum, etc., a typical PTR-MS instrument consists of the following major components:

[0004] Reagent ion source:

[0005] Reagent ions are formed in a reagent ion source. Many PTR-MS instruments employ a hollow cathode ion source, which is supplied with a suitable source gas (e.g., H2O vapor, O2, N2, inert gas, etc.), but various other designs have been described (e.g., tip discharge, planar electrode discharge, microwave discharge, radioactive ion source, etc.). Advantageous ion sources produce high purity reagent ions due to their complex design or due to the use of mass filters.

[0006] Reaction chamber / drift tube:

[0007] In the PTR reaction chamber, chemical ionization of the analyte occurs via interaction with the reagent ions. The reaction chamber is also commonly referred to as a drift tube or reaction zone. When a certain flow rate of gas containing the analyte is continuously injected, the electric field attracts the ions along the drift tube. Typically, air containing trace impurities (e.g., trace amounts of volatile organic compounds) is analyzed by PTR-MS, but many other matrices containing compounds of interest (e.g., residual impurities in purified gases, gas standards, etc.) have been successfully studied using various reagent ions. In some embodiments, the matrix containing the analyte (e.g., air with trace amounts of volatile organic compounds) is diluted with a buffer gas before being injected into the drift tube (e.g., for the purpose of simple dilution, for use with specific reagent ions, etc.).

[0008] Some common reactions between reagent ions and analytes that occur in the reaction chamber are:

[0009] - non-dissociative or dissociative proton transfer reactions where AH + is the reagent ion (in most cases H2O.H + ) and BC is the analyte:

[0010] AH + +BC→A+BC.H +

[0011] AH + +BC→A+B+CH +

[0012] - non-dissociative or dissociative charge transfer reactions where A + For reagent ions (such as O2 + 、NO + , Kr + etc.) and BC is the analyte:

[0013] A + +BC→A+BC +

[0014] A + +BC→A+B+C +

[0015] -Clustering reaction, where A + For reagent ions (such as H3O + 、NO + etc.) and BC is the analyte:

[0016] A + +BC→BC.A +

[0017] Additionally, other types of reactions can occur (e.g., ligand exchange, H + extraction, etc.).

[0018] The most common drift tube consists of a series of annular electrodes electrically connected via resistors of equal resistance so that a DC voltage U can be applied across the drift tube of length d, resulting in an electric field strength E = U / d (V / cm).

[0019] Mass Analyzers and Detectors:

[0020] Since the mass analyzer is typically operated in a high vacuum or ultra-high vacuum state, there is a transition zone between the reaction chamber and the mass analyzer to account for the pressure difference between the two regions. Various types of mass analyzers have been employed in PTR-MS instruments. The most prominent example of a low-resolution mass analyzer is a quadrupole mass filter, while for high mass resolution measurements, a time-of-flight (TOF) analyzer is typically used for PTR-MS. However, the use of other types of mass analyzers, such as, for example, ion trap analyzers, has also been reported, and even MS can be implemented. n (Multistage mass spectrometry) The mass analyzer separates the ions injected from the drift tube according to their m / z and uses a suitable detector (eg, secondary electron multiplier, microchannel plate, etc.) to quantify the yield of the separated m / z ions.

[0021] Current state of the art

[0022] One of the first PTR-MS instruments, introduced in 1995 (A. Hansel, A. Jordan, R. Holzinger, P. Prazeller, W. Vogel, W. Lindinger, Proton transfer reaction mass spectrometry: on-line trace gas analysis at the ppb level. International Journal of Mass Spectrometry and Ion Processes 149 / 150 (1995) 609-619), employed a hollow cathode reagent ion source in line (on the same central axis) with an adjacent drift tube. Perpendicular to this axis, the sample inlet was mounted at the beginning of the drift tube. Since this early concept remains state of the art in the vast majority of the hundreds of PTR-MS instruments in use today, it will be discussed in more detail in the "Detailed Description of the Invention" section.

[0023] Two rare exceptions to the common design have been disclosed by Breitenlechner (An Instrument for Studying the Lifecycle of Reactive Organic Carbon in the Atmosphere. Analytical Chemistry 89 (2017) 5824-5831) and Krechmer (Evaluation of a new vocus reagent-ion source and focusing ion-molecule reactor for use inproton-transfer-reaction mass spectrometry. ChemRxiv (2018) preprint). Breitenlechner et al. developed a new PTR-MS instrument specifically designed for atmospheric chemistry at very high sample gas flow rates. Their aim was to place the sample inlet as much as possible in the direction of the central axis of the reaction chamber. However, this inevitably led to a conflict with the position of their corona discharge reagent ion source, which should also be in line with the central axis of the reaction chamber. The solution they proposed was an embodiment in which both the ion source and the sample inlet were pointed in the direction of the central axis of the reaction chamber at a slightly off-axis angle. Krechmer et al. proposed a different design in which the inlet line was pointed exactly in the direction of the central axis of the reaction chamber, while the ion source consisted of two conical surfaces (with the plasma burning therebetween) surrounding the inlet line, thereby pointing in the direction of the central axis of the reaction chamber at a slightly off-axis angle.

[0024] Another example of resolving the conflict between the ion source and the sample inlet pointing substantially in the direction of the central axis of the reaction chamber is given in US 7 095 019 B1. There, a different type of instrument than a PTR-MS instrument is described, and the conflict is resolved by placing the ion source at an angle of about 45° to the central axis. This choice results in very limited space in the sample inlet region.

[0025] In addition, WO 2018 / 050962 A1 discloses a general multi-method ionization device using chemical ionization and a system using such a device, which is provided with a reaction chamber for ion formation of a reagent substance, which is also not a PTR-MS instrument. The purpose of the ionization instrument in WO 2018 / 050962 A1 is to detect substances with extremely high sensitivity, which is achieved by positioning multiple ionization sources in and around the reaction zone. The instrument in WO 2018 / 050962 A1 can answer the question of whether a substance is present in a sample, but cannot quantify the compound and is therefore not a PTR-MS instrument.

[0026] Until now, there have been two main problems with PTR-MS reagent ion source design:

[0027] a) Although switching reagent ions (e.g. from H3O + To O2 + ) is relatively fast, but still takes a lot of time. Based on literature reports and the inventor's experience, after about 3 to 4 seconds, the main switching process has been completed (the mass flow controller has switched the source gas, the gas in the ion source has been partially replaced and the voltage and pressure have been changed). However, in order to obtain high-purity reagent ions, up to tens of seconds are required, for example to remove residual humidity in the ion source. This can be considered a major disadvantage of PTR-MS in direct comparison with techniques such as selected ion flow tube-mass spectrometry (SIFT-MS), in which a quadrupole mass filter is used to select reagent ions and can be switched in an instant. Installing a mass filter similar to SIFT-MS is not an option for PTR-MS, because the mass filter can never achieve 100% transmission efficiency, and therefore one of the main advantages of PTR-MS will be lost: extremely high sensitivity. To date, no satisfactory solution has been proposed for this problem.

[0028] b) According to the prior art, for proper performance, it is necessary to align the ion source and the sample inlet with the central axis of the reaction chamber. Such an arrangement is difficult because the two devices cannot be in the same position at the same time. The reasons for this alignment are that i) extremely high reagent ion currents are required to achieve the excellent sensitivity of the PTR-MS instrument (the ion source should inject the reagent ions on the central axis of the reaction zone), and

[0029] ii) Contact of the sample gas with the inlet line walls should be avoided due to possible condensation and conversion effects (ie a straight inlet without corners, T-pieces, valves, mass flow controllers, etc. is advantageous).

[0030] Brief description of the invention

[0031] It is therefore an object of the present invention to provide an IMR / PTR-MS design which solves the problem mentioned in a) and meets the requirements mentioned in i) and ii) without introducing disadvantages.

[0032] This object is achieved by a device for ion-molecule-reaction mass spectrometry and / or proton-transfer-reaction mass spectrometry, comprising

[0033] - Sample gas inlet,

[0034] -Ion source part,

[0035] - a first ion source,

[0036] - reaction chamber,

[0037] - a mass analyser, wherein the reaction chamber and the mass analyser are arranged along a central axis, characterized in that a second ion source,

[0038] wherein the sample gas inlet is arranged to introduce gas into the ion source portion substantially along the central axis and is connected to the reaction chamber;

[0039] wherein the first ion source and the second ion source are arranged substantially in a plane in front of the reaction chamber to emit reagent ions into the ion source portion substantially perpendicular to the central axis;

[0040] The apparatus further comprises at least one electrode such that reagent ions emitted from the first or second ion source into the ion source portion can be deflected substantially in a downstream direction of the central axis into the reaction chamber.

[0041] The terms "central axis" and "axis of the reaction chamber" are used substantially synonymously. The term "in the downstream direction of the central axis" means "in the direction of the central axis and in the downstream direction".

[0042] This object is further solved by a method of operating an apparatus for ion-molecule-reaction mass spectrometry and / or proton-transfer-reaction mass spectrometry according to the description, said method being characterized by the following steps:

[0043] - introducing a sample gas into the ion source portion via a sample gas inlet in the direction of a central axis of the reaction chamber;

[0044] - sequentially generating at least two different reagent ions in at least two ion sources, wherein a particular type of reagent ion is generated in a respective ion source;

[0045] - applying a voltage to at least one electrode at the outlet of each ion source, wherein a particular voltage value causes the corresponding reagent ions to be injected into the ion source portion and another particular voltage value causes them to be repelled back into the corresponding ion source;

[0046] - applying a voltage to at least one electrode located upstream and near the sample gas inlet, wherein the electrode causes a repulsive force on the reagent ions, and applying a voltage to at least one electrode located downstream and near the reaction chamber, wherein the electrode causes an attractive force on the reagent ions, so that the reagent ions are injected into the reaction chamber substantially in a downstream direction of the central axis of the reaction chamber;

[0047] - Introducing reagent ions and / or sample gas into a reaction chamber, wherein after the reaction chamber the analyte or sample gas is analyzed using a mass analyzer.

[0048] With regard to the device, there are a number of preferred embodiments.

[0049] In a preferred embodiment, the apparatus features at least one further ion source arranged to emit reagent ions substantially perpendicularly to the central axis.

[0050] With regard to the orientation of the at least two ion sources, the axes (e.g. central axes or longitudinal axes) of at least two (preferably at least three) ion sources are substantially perpendicular to the central axis of the reaction chamber. In a preferred embodiment, the ion sources are substantially arranged in a plane substantially perpendicular to the central axis of the reaction chamber.

[0051] The apparatus may also be characterized in that the electrodes are connected to a switching arrangement such that emitted reagent ions from one ion source are deflected onto the central axis, while reagent ions from any other ion source are repelled back into the corresponding ion source.

[0052] Preferably, the ion source is located in the region of the ion source portion, wherein the reaction chamber is downstream and preferably adjacent to the ion source portion.

[0053] In a preferred embodiment, the apparatus comprises three ion sources, wherein the first ion source is capable of generating H3O from H2O vapor. + , the second ion source can generate O2 from O2 + , and the third ion source can generate NO from N2 and O2 + The angle between adjacent ion sources can be measured as 120°.

[0054] Preferably, the ion source is a hollow cathode ion source.

[0055] In a preferred embodiment, a sample gas inlet is provided that exhibits a first portion of the sample gas inlet and a second portion of the sample gas inlet, wherein the second portion of the sample gas inlet is adjacent to the first portion of the sample gas inlet. Preferably, the sample gas inlet is in the direction of a central axis of the reaction chamber, wherein the sample gas inlet is substantially parallel to the central axis, preferably in the immediate vicinity of the central axis.

[0056] It is particularly preferred that the second part of the sample gas inlet is downstream of the first part of the sample gas inlet, wherein the diameter of the second part of the sample gas inlet is preferably smaller than the diameter of the first part of the sample gas inlet, wherein the first and second parts of the sample gas inlet are fluidically connected.

[0057] Preferably, the second portion of the sample gas inlet is fluidly connected to the ion source portion, and the ion source portion is fluidly connected to the reaction chamber.

[0058] In one embodiment, the apparatus comprises a sample inlet bypass line, wherein the sample inlet bypass line is arranged substantially perpendicular to the sample gas inlet.In a two-part sample gas inlet, the sample inlet bypass line is preferably fluidly connected to a first part of the sample gas inlet.

[0059] Preferably, the gas line is arranged substantially perpendicular to the sample gas inlet.In a two-part sample gas inlet, the gas line is preferably fluidly connected to the second part of the sample gas inlet.

[0060] A particularly preferred embodiment provides that the ion source portion consists of at least two electrodes (preferably at least three electrodes), wherein at least one electrode is located opposite each ion source and / or at least one electrode is located near the second portion close to the sample gas inlet and / or at least one electrode is located close to the reaction chamber.

[0061] The electrodes constitute a chamber-like entity called an ion source portion, which comprises an ion source outside the chamber-like entity, wherein the ion source is fluidically connected to the interior of the chamber-like entity. Preferably, the axis of the ion source points substantially towards the center of the ion source portion.

[0062] At least two ion sources may be positioned between an electrode located in close proximity to the second portion of the sample gas inlet and an electrode located in close proximity to the reaction chamber.

[0063] Preferably, at least two ion sources comprise at least one electrode, by means of which reagent ions can be injected into the ion source section and / or repelled back into the respective ion source.

[0064] The sample gas inlet is preferably arranged along the central axis and opens into the reaction chamber.

[0065] In one embodiment, at least one electrode is located opposite each ion source and / or at least one electrode is located upstream and near the sample gas inlet and one electrode is located downstream and near the reaction chamber.

[0066] Preferably, each ion source comprises at least one electrode at the outlet.

[0067] In relation to the method, it may be provided that a voltage is applied to at least one electrode opposite the at least two ion sources, wherein the electrode induces a repulsive force for the reagent ions.

[0068] It is particularly preferred that the control device controls the voltage applied to the electrodes, wherein the control device controls which reagent ions generated in the corresponding ion source will be injected into the ion source part and / or which reagent ions generated in the corresponding ion source will be repelled back into the corresponding ion source.

[0069] In a particular variation, the control device adapts the parameters of the device so that the device functions as an atmospheric pressure interface mass spectrometer as required, wherein the parameters include at least the voltage applied to the electrodes, wherein the control device controls the ions generated in the ion source to be repelled back into the corresponding ion source, or the ion source is turned off by the control device so that no reagent ions are generated.

[0070] Further embodiments and advantages are explained with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 A schematic diagram of the prior art of an IMR / PTR-MS instrument is shown.

[0073] Figure 2 A schematic diagram of an exemplary IMR / PTR-MS instrument according to the present invention is shown.

[0074] Figure 3 A schematic diagram of an exemplary reagent ion source arrangement having three ion sources is shown.

[0075] Figure 4 A schematic diagram of part of an ion source according to the present invention is shown.

[0076] Figure 5 A schematic diagram showing an embodiment in which one reagent ion source is configured to inject reagent ions into an ion source portion and one reagent ion source is configured to block ions from entering the ion source portion.

[0077] Figure 6A schematic diagram of a prototype constructed according to the present invention is shown. DETAILED DESCRIPTION OF THE INVENTION

[0079] Figure 1 1 is a schematic overview of the prior art, wherein the reagent ion source comprises a first part 101 and a second part 102, a drift tube 103, a mass analyzer 104 and a sample inlet 105. Water vapor originating from a tank filled with purified water enters the first part 101 of the ion source. In the first part 101, a hollow cathode discharge converts H2O molecules into a series of product ions: H2O + , H + 、H2 + OH + and O + Since highly pure H3O is ultimately required in the second portion 102 of the ion source (also referred to as the “source drift” region), + The reagent ions, and thus the product ions and water vapor from the first portion 101 (both transferred to the second portion 102 via gas flow and / or electric field) undergo various ion-molecule reactions, which result in H3O + The purity level is above 99%. The underlying ion chemistry has been discussed in detail in the literature. + The reagent ions are injected into the drift tube 103 where they can interact with the analyte-containing gas (eg, air with trace compounds) introduced into the drift tube via the sample inlet 105 .

[0080] It has been shown that this ion source design can also be used to generate very pure ions in addition to H3O by switching the source gas and adjusting the current and voltage applied to the ion source and the pressure in the ion source. + Other reagent ions, such as NO + 、O2 + , Kr + 、Xe + NH4 + OH - wait.

[0081] The present invention relates to the front end of an IMR / PTR-MS instrument. Figure 2 denoted by 201. The sample gas is drawn into the instrument via sample gas inlets 202, 206 (also referred to as sample inlets), which are substantially in the direction of the central axis A from the reaction chamber 203 to the mass analyzer 204. The sample inlet bypass line 205 allows the sample inlet flow rate to be adjusted while keeping the flow rate into the reaction chamber 203 constant. That is, a vacuum pump (a membrane pump, a vortex pump, a multi-stage turbomolecular pump, etc.) is connected to the sample inlet bypass line 205.

[0082] In a preferred embodiment, a mass flow controller, valve or similar device allowing the air flow to be regulated is installed between the sample inlet bypass line 205 and the vacuum pump. If this flow regulating device is completely closed so that suction is not generated via the sample inlet bypass 205, only a minimum amount of gas is sampled (the sample gas flow entering the reaction chamber 203). If the flow regulating device is open, almost any sample inlet flow rate above the minimum value can be set. Typically, the IMR / PTR-MS reaction chamber is operated between 0.1 and 100 hPa, preferably between 1 and 10 hPa. This vacuum is usually maintained by one or more vacuum pumps connected to one or more pumping ports of the reaction chamber 203, and determines the minimum gas flow required to operate the instrument, that is, the pressure in 203 is generated by the gas entering and being pumped out. There is also a second part of the sample gas inlet 206 on the same straight line of the central axis A. Preferably, the inner diameter of this part (adjacent to the connection point of the sample inlet bypass 205) is smaller than the first part of the sample gas inlet 202, so that the gas flow through 206 is limited.

[0083] Gas line 207 is connected to the second part of sample gas inlet 206 and to a vacuum pump, which can be the same vacuum pump connected to 205 or another pump of the same or different type. Preferably, a pressure controller, a valve or any gas flow regulating device is interconnected between gas line 207 and the vacuum pump. Via the gas flow / suction through gas line 207, the pressure in reaction chamber 203 (which itself is evacuated by a vacuum pump) can be regulated.

[0084] The sample gas flows into the ion source section 208. This section can be a part of the reaction chamber 203 or a separate part. At least two reagent ion sources 209 are installed in this section substantially perpendicular to the axis A, i.e., in plane B. The ion source 209 can be any IMR / PTR-MS reagent ion source (e.g., tip discharge, planar electrode discharge, microwave discharge, radioactive ion source, etc.). In a preferred embodiment, the ion source 209 is a hollow cathode ion source.

[0085] Figure 3 A schematic diagram of an exemplary embodiment in the direction of the central axis A is shown. Here, three reagent ion sources 209 are installed in a plane B substantially perpendicular to the axis A at 0 °, 120 ° and 240 ° (angles). In this exemplary embodiment, the ion source portion 208 has a circular cross section. Any other cross section is also possible, such as any combination of triangle, rectangle, polygon, ellipse, curve and / or straight line form. Any position of the ion source 209 is possible, such as relative to each other or at any angle to each other. The number of ion sources 209 must be at least two.

[0086] Figure 4 A schematic diagram of an exemplary embodiment of an ion source part 208 is shown. In the figure, sample gas is introduced from the left side via orifice 301 (connected to sample gas inlet 206, not shown here). A DC voltage can be applied to electrode 302. At position 303 is at least one electrode (ion lens) with an orifice, where a DC voltage can be applied. By applying a suitable voltage to electrode 303, the reagent ions produced in the reagent ion source 209 can be injected into the ion source part 208, or repelled so that they do not enter the ion source part 208. Electrode 304 can be the first electrode of an IMR / PTR-MS drift tube or an ion lens for injecting reagent ions into a reaction chamber. 305 is an electrode opposite the reagent ion source, which can be, for example, a metal plate or an electrically conductive inner shell of an ion source part 208. In some embodiments, there is no electrode 305. In a preferred embodiment, the function of electrode 305 is replaced or supplemented by an electrode 303 of at least one other ion source 209 except the ion source 209 currently injecting reagent ions. By applying appropriate potentials / voltages to 302 , 303 , 304 , and 305 , reagent ions may be introduced into the IMR / PTR-MS reaction chamber, as schematically indicated by arrow 306 .

[0087] If at least two reagent ion sources 209 are installed in the ion source section 208 according to the present invention, the reagent ions can be selected by simply changing the voltage applied to the electrodes. Preferably, the voltage that is changed is the voltage of the ion source exit lens 303.

[0088] exist Figure 5 In the figure, two reagent ion sources are schematically shown, in which the reagent ions of one ion source are repelled (do not enter the ion source part and ultimately do not enter the IMR / PTR-MS reaction chamber), while the reagent ions produced by the other ion source are injected into the ion source part and ultimately enter the IMR / PTR-MS reaction chamber. That is, if, for example, one reagent ion source continuously produces one type of reagent ions and the other reagent ion source continuously produces another type of reagent ions, the reagent ions used for chemical ionization in the IMR / PTR-MS reaction chamber can be switched very quickly by simply changing the electrode voltage. In sharp contrast to existing designs, it is not necessary to perform time-consuming source gas switching or pressure regulation. It has been shown that the reagent ion yield entering the reaction chamber has an intensity comparable to that of a common single ion source in a straight line with the central axis of the reaction chamber, that is, the intensity loss due to the vertical position is negligible.

[0089] In a preferred embodiment, at least three reagent ion sources are installed, which continuously generate at least H3O + 、NO+ and O2 + .

[0090] In another embodiment, at least four reagent ion sources are installed, each of which continuously generates at least H3O + NH4 + 、NO + and O2 + .

[0091] Obviously, if it is used for long-term measurement, it is foreseeable that there will be no need to switch reagent ions, that is, only one type of reagent ions is needed, and all reagent ion sources except the reagent ion source that produces the required reagent ions can be turned off to save source gas and prevent wear effects. However, in this case, fast switching is not possible.

[0092] In another embodiment, all reagent ion sources are turned off or set so that they do not inject reagent ions into the reaction zone. In this mode of operation, the novel front end can act as an APi (atmospheric pressure interface) device, and the IMR / PTR-MS instrument can be used to analyze atmospheric ions. In this case, chemical ionization reactions between reagent ions and sample gas do not occur in the reaction zone, and the reaction chamber only transmits atmospheric ions to the mass analyzer. Similarly, only the potential and voltage need to be changed to achieve this mode of operation so that atmospheric ions are introduced into the reaction zone and then introduced into the mass analyzer.

[0093] Exemplary embodiments:

[0094] Figure 6 A schematic diagram of a prototype embodiment is shown in FIG, which serves only as an example and in no way should the invention be limited to this embodiment.

[0095] In the inlet section 401, an opening 402 is drilled in the direction of the central axis A. This opening 402 is equipped with a thread to screw in a 1 / 16 inch sample inlet line with an inner diameter of 1 mm (e.g., made of PEEK (polyetheretherketone), passivated stainless steel, PTFE, etc.). An opening 403 is drilled perpendicular to the opening 402 and is connected to a membrane vacuum pump via a mass flow controller. By adjusting the mass flow controller, the amount of gas containing the analyte sampled by the instrument can be adjusted from the minimum value required to operate the IMR / PTR-MS instrument (10 to 100 cm3 / min under standard conditions for the prototype instrument) to the maximum pumping power of the membrane vacuum pump. Adjacent to the borehole 402, there is a borehole 404 with a smaller diameter in the direction of the central axis A. Perpendicular to the borehole 404, there is a borehole 405, which is connected to the same vacuum pump as the borehole 403, but has an interconnected pressure controller instead of a mass flow controller. By adjusting this pressure controller, the (obtained) pressure in the IMR / PTR-MS reaction chamber can be adjusted. A second portion of the inlet line 404 terminates at an electrode / ion lens 406 at the beginning of an ion source portion 407 .

[0096] Three hollow cathode reagent ion sources 408, 409 and 410 (the latter two are only shown in the schematic diagram) are respectively installed in plane B at an offset angle of 120° perpendicular to the central axis A (compare Figure 3 ). All three reagent ion sources have the same design: a first ionization chamber 411 and a second ionization chamber 412. Both ionization chambers are substantially made of a conductive material. Preferably, the conductive material is stainless steel, such as stainless steel type EN 1.4301, 1.4405 or 1.4407. One or more source gases are introduced into the first chamber 411 via a mass flow controller, where a hollow cathode discharge ionizes the source gas. Typical source gases are for producing H3O + H2O vapor, used to generate O2 + O2, used to produce NO + A mixture of N2 and O2 is used to produce NH4 + The mixture of N2 and H2O vapor. Ions and neutral substances then enter the second ionization chamber 412, where they react via ion-molecule reaction and form a specific type of high-purity reagent ions. Ionization chamber 412 is connected to a vacuum pump via an electronically controlled (proportional) valve so that pressure can be adjusted. An electric field can be applied to ionization chambers 411 and 412 to control hollow cathode discharge, transmission ions and control ion-molecule reaction. At least one ion lens at the outlet of chamber 412 entering ion source portion 407 can prevent (repel) or transmit ions.

[0097] Each of the three reagent ion sources 408, 409 and 410 continuously produces a specific type of reagent ion. However, the voltage applied to the exit ion lens of only one ion source is set so that these reagent ions can enter the ion source portion 407. The remaining two reagent ion types are blocked from entering the ion source portion 407 by the voltage applied to the exit ion lens. After entering the ion source portion 407, the reagent ions are attracted in the direction of the central axis A by electric fields. These electric fields are generated, for example, by the electrode 406 and the annular electrode of the reaction chamber 413.

[0098] In addition, the electrodes at the exit of the chamber 412 can generate electric fields that extend to some extent into the ion source portion 407. That is, a repulsive potential is applied at the exit electrodes of those reagent ion sources that are configured so that they do not inject reagent ions into the ion source portion 407. This repulsive potential prevents the reagent ions from leaving the corresponding ion source.

[0099] On the other hand, it pushes the reagent ions from the other reagent ion source toward the central axis A. In other words, the reagent ions injected into the ion source portion 407 from one "active" reagent ion source 408 are repelled by the electrode 406 and the exit electrodes of the other two "inactive" reagent ion sources and attracted into the reaction chamber 413. For example, if the reagent ion source at 0° (angle) produces H3O + The outlet electrodes of the remaining two reagent ion sources at 120° and 240° are arranged so that they do not inject reagent ions into the ion source portion 407. The repulsive electric field generated by these two electrodes helps to inject the H3O from the reagent ion source at 0° into the ion source portion 407. + The reagent ions are kept close to the central axis A, i.e., they are forced to move close to the Figure 4 On the flight path shown by arrow 306 in FIG.

[0100] In this exemplary embodiment, reaction chamber 413 comprises a series of annular electrodes 414 with constant orifice diameter and annular electrodes 415 with reduced orifice diameter of adjacent series. DC voltage is applied on electrodes 414 and 415, so they serve as IMR / PTR-MS drift tubes. The RF voltage applied in addition allows focusing ions and therefore prevents ion loss. Reaction chamber is evacuated to 1 to 10 hPa by the vacuum pump connected to the pumping port in 413. Finally, ions are transferred to region 416, which represents differential pumping region, TOF mass analyzer and microchannel plate detector.

[0101] With the present invention, the sample gas can be introduced in line with the central axis of the reaction chamber of the IMR / PTR-MS instrument. Although the inlet gas flow rate and the pressure in the reaction chamber can be fully controlled, the sample gas does not pass through any valves, mass flow controllers or similar devices on its path into the reaction chamber. In addition, there are no bends or kinks that the sample gas must pass through, but it can enter the reaction chamber directly. This greatly improves the response and decay time of the instrument because wall effects such as sample-wall interactions are suppressed. Combined with the possibility of extremely fast reagent ion switching, since at least two reagent ion sources produce reagent ions simultaneously, the IMR / PTR-MS instrument according to the present invention is significantly faster, more selective and sensitive than existing designs.

[0102] By switching off all reagent ion sources or arranging them so that none of them inject reagent ions into the reaction zone, the front end according to the invention acts as an APi. This is only possible because the sample gas inlet design inhibits contact between the sample gas and the walls, which would inevitably lead to losses of (atmospheric) ions. An instrument equipped with such a front end is therefore extremely cost-effective, since two types of instruments are combined into one: APi-MS and IMR / PTR-MS.

Claims

1. An apparatus for ion-molecule-reaction mass spectrometry and / or proton-transfer-reaction mass spectrometry, comprising - Sample gas inlet, - an ion source portion (208), - a first ion source, - a reaction chamber (203), - a mass analyzer (204), The reaction chamber (203) and the mass analyzer (204) are arranged along a central axis A, characterized in that: Also comprising a second ion source, wherein the sample gas inlet is arranged to introduce gas into the ion source portion (208) along the central axis A and is connected to the reaction chamber (203); wherein the first ion source and the second ion source are arranged in a plane B in front of the reaction chamber (203) to emit reagent ions perpendicularly to the central axis A into the ion source portion (208); The apparatus further comprises at least one electrode for enabling the reagent ions emitted from the first ion source or the second ion source into the ion source portion (208) to be deflected in a downstream direction of the central axis A into the reaction chamber (203), wherein each of the first ion source and the second ion source comprises at least one electrode, by means of which reagent ions can be injected into the ion source portion and / or repelled back into the corresponding ion source, The electrodes are connected to a switching arrangement such that emitted reagent ions from one ion source are deflected onto the central axis, while reagent ions from any other ion source are blocked from entering the reaction chamber.

2. The device according to claim 1, characterized in that: Two ion sources are arranged in the plane B, which is perpendicular to the central axis A of the reaction chamber (203), wherein the two ion sources consist of the first ion source and the second ion source.

3. The device according to claim 1, characterized in that: At least one further ion source arranged to emit reagent ions perpendicular to said central axis A is included.

4. The device according to claim 3, characterized in that Three ion sources are arranged in a plane B, which is perpendicular to the central axis A of the reaction chamber (203), wherein the three ion sources consist of the first ion source, the second ion source and the additional ion source.

5. The device according to claim 3, characterized in that: Three ion sources are included, and the three ion sources are composed of the first ion source, the second ion source and the additional ion source, wherein each of the three ion sources is capable of generating one type of ion in the group of H3O+, O2+ and NO+, and wherein each of the three ion sources generates different types of ions.

6. The device according to any one of claims 1 to 5, characterized in that The sample gas inlet is arranged along the central axis A and leads to the reaction chamber (203).

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