A Sample Injector for a Gas Chromatograph

Abstract

A sample injector 1 for a gas chromatograph (40, fig 1) comprises a body 10 defining a sample chamber configured to receive a sample; and a plurality of heating elements for heating the body. Each hea

Description

This invention relates to gas chromatography and, more particularly, to a sample injector for a gas chromatograph (GC) and a method for the operation thereof. BACKGROUND Injectors are used to introduce samples into chromatographic columns within gas chromatographs. A sample is introduced to an internal cavity of the injector using a syringe. A heating element is used to heat the injector in order to heat and vaporize the sample, which can then be transferred to the analytical column placed inside the oven of the gas chromatograph for the chromatographic separation. A proper temperature distribution along the injector (temperature profile) is fundamental for the precision and accuracy of the analysis as it determines the correct introduction, vaporization, and transfer of the sample. The temperature profile of an injector, especially at its extremes, is sensitive to the external conditions. In particular, an area of the injector in contact or adjacent to the oven may become overheated by the heat of the oven when the oven is at high temperature or being too cold when the oven is kept at low temperature. Cold spots in injectors may result in sample discrimination (i.e. incomplete transfer). Conversely, overheated regions may affect the integrity of the internal surfaces and may cause sample degradation or adsorption phenomena. A heating element with a single control may not be able to correctly manage the temperature profile of the injector, especially while the oven is performing temperature cycles. A gas chromatographic oven assembly is described in US 2003 / 0037592 A1, the entire contents of which are herewith incorporated in this document. An injection port for a gas chromatograph is described in US 9 632 064 B2, the entire contents of which are herewith incorporated in this document. EP 1 719 958 A1 refers to the problem of cold spots. It discloses a direct heating tube which directly heats a fluid during the passage of the fluid, characterized in that in a desired 10 07 25 portion of the tube to be heated, a second heated tube which is connected to a first heated tube is provided outside the first heated tube. Existing systems may provide limited control options, may not compensate for overheating and / or may not allow for environmental changes to be taken into account. Existing systems may also lack the ability to change the temperature profile of the injector during different phases of operation. The present invention aims to provide an improved sample injector for a gas chromatograph and method of heating a sample injector for a gas chromatograph, overcoming the formation of unwanted cold or overheated spots. Another aim is to provide a sample injector in which the temperature of different areas of the injector can be modified, throughout operation of the sample injector or for a specified phase of operation, in order to optimize injection performances and allow the operation of the injector to be tailored to the type of sample to be analysed. SUMMARY The present invention provides a sample injector, method and gas chromatograph assembly according to the appended claims. In any method disclosed herein, the sample injector may be any sample injector according to the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the disclosure will now be described, by way of example only, with reference to the following non-limiting figures in which: Figure 1 is a schematic diagram of a gas chromatograph comprising a sample injector according to the present disclosure; Figure 2 is a schematic section view showing a first sample injector according to the present disclosure; Figure 3 is a schematic section view showing the sample injector of Figure 2 in use; and Figure 4 is a schematic diagram showing a second sample injector according to the present disclosure; 10 07 25 Figure 5 is a schematic cross section diagram of a sample injector of the same type as that shown in Figure 4. DETAILLED DESCRIPTION 5 Figure 1 shows a schematic diagram of a gas chromatograph 40 comprising a sample injector 1 according to the present disclosure. The sample injector 1 is fluidly connected via a tube 42 to a gas chromatography (GC) column 43 arranged in an oven 41. The tube 42 fluidly couples or forms part of the gas chromatography column 43 of the gas chromatograph 40. A controller 44 is provided for control of the sample injector 1 and / or the 10 gas chromatograph 40. To perform a scientific analysis within the column 43, a material sample 45, typically in the form of a liquid, is injected into the sample injector 1, along with a carrier gas (which may also be referred to as a mobile phase). The sample is heated by the sample injector 1 and 15 injected into the column 43 of oven 41, which separates the sample 45 into its individual components. The individual components then travel out through exit port 46 for analysis, for example by a mass spectrometer. Figures 2 and 3 show a schematic diagram of a first sample injector according to a non- 20 limiting embodiment of the present disclosure. The sample injector may be a Programmed Temperature Vaporizer (PTV) injector, for example. The sample injector 1 comprises a body 10 defining a sample chamber 11 configured to receive a sample. As shown in Figure 2, the body 10 may be in the form of an elongate 25 tube defining a longitudinal axis 15, the body 10 having an inlet end 12 and a downstream end 13, the downstream end 13 being distal to the inlet end 12 along the longitudinal axis 15. A septum 50 may be arranged at the inlet end 12 of the body 10 for receiving the sample, 30 for example by inserting a syringe needle through the septum 50 to deliver a liquid sample to the sample chamber 11. A liner 11 a may be arranged in the sample chamber 11, the sample being received inside the liner 11a in use. The downstream end 13 of the injector may comprise an injection portion 14 to be received in a gas chromatograph 40 in use, for example as in the embodiment shown in Figures 2 and 3. 10 07 25 As in Figure 2, the body 10 of the sample injector 1 may comprise a plurality of zones including an inlet zone 20a arranged proximal to the inlet end 12 of the body, a downstream zone 20c arranged proximal to the downstream end 13 of the body and an intermediate zone 20b arranged between the inlet zone 20a and the downstream zone 20c. 5 The sample injector 1 comprises a plurality of heating elements for heating the body 10. Each heating element of the plurality of heating elements is configured to be controlled independently of each other heating element of the plurality of heating elements. For example, each heating element of the plurality of heating elements may be configured to be 10 energised independently of each other heating element of the plurality of heating elements. In the embodiment shown in Figure 2, the sample injector 1 comprises three heating elements. The plurality of heating elements may be configured such that each heating element of the 15 plurality of heating elements is configured to heat a different zone of the plurality of zones, for example by being arranged around or adjacent to a corresponding zone of the plurality of zones. As in Figures 2 and 3, the plurality of heating elements may comprise an inlet heating 20 element 30a arranged to heat the inlet zone 20a, a downstream heating element 30c arranged to heat the downstream zone 20c and an intermediate heating element 30b arranged to heat the intermediate zone 20b. As shown in Figure 2, the plurality of heating elements may be arranged in series along the body 10 (i.e. in series in a direction aligned with the longitudinal axis 15 of the body 10). 25 In the embodiment of Figure 2 and 3, each of the heating elements is a heatable coil arranged around the body 10. The coil density of the heating elements in this embodiment is uniform along the longitudinal length of the body 10. 30 The sample injector 1 may comprise a controller 44 (see Figure 1) configured to independently control each heating element of the plurality of heating elements. As shown in Figure 2, a plurality of temperature sensors may be provided. Each temperature sensor 31a, 31b, 31c of the plurality of temperature sensors may arranged adjacent to or in contact with a corresponding zone of the plurality of zones such that the controller 44 can 35 be configured to monitor the temperature of each zone 20a, 20b, 20c of the plurality of 10 07 25 zones separately. The controller 44 may be configured to control a current applied to each of the heating elements 30a, 30b, 30c based on inputs from the corresponding temperature sensors arranged adjacent to each zone. The temperature sensors may be thermocouples. 5 Ina further embodiment, a gas chromatograph comprises a sample injector 1 according to the present disclosure. Figure 3 shows the sample injector of Figure 2 in use as part of a gas chromatograph 40. In use, the injection portion 14 of the injector 1 may be received in an oven of a gas chromatograph 40. The sample may be transferred from the injector 1 to the gas chromatography column 43, an upper portion of which is arranged inside in the 10 injection portion 14 of the body. As shown in Figure 3, forced air cooling apparatus 3 may be provided around the injector body 1 to allow further control of the temperature of the injector 1. Figures 4 and 5 show schematic diagrams of a second sample injector 101 according to a 15 further non-limiting embodiment of the present disclosure. Differences between the second sample injector and the first sample injector are described below. All other features of this further embodiment may be as described above. The second sample injector may be a Split / Splitless (SSL) injector. 20 As shown in Figures 4 and 5, the sample injector 101 may comprise a plurality of casings and a plurality of temperature sensors. Each heating element 130a, 130b, 130c of the plurality of heating elements of the sample injector 101 may comprise a resistor in the form of a cartridge or cylinder arranged adjacent to and extending along a zone of the body 10 to be heated by that heating element. Each casing 132a, 132b, 132c of the plurality of 25 casings may be in the form of a generally tubular block comprising an inner cavity, the casing being arranged around the body 110 of the injector (as in the embodiment shown in Figures 4 and 5), and being configured to receive within the internal cavity a heating element 130a, 130b, 130c of the plurality of heating elements, the zone 20a, 20b, 20c of the body 10 to be heated by the heating element, and one temperature sensor 131a, 131b, 30 131c of the plurality of temperature sensors, such that these components are all substantially surrounded by the casing. The plurality of casings and the plurality of heating elements may be arranged in series along the body 10. The arrangement and configuration of the plurality of heating elements and / or the plurality of temperature sensors may otherwise be as described above. 10 07 25 The present disclosure also provides a method of heating a sample injector for a gas chromatograph, the method comprising providing a plurality of heating elements configured to heat a body of the sample injector and controlling each heating element of the plurality of heating elements independently of each other heating element of the plurality of heating 5 elements. The sample injector may be any sample injector 1,101 according to the present disclosure. The method may comprise measuring a parameter indicative of a temperature of a first zone of the body 10, 110 and controlling a first heating element of the plurality of heating 10 elements to heat the first zone to one or more temperature setpoints. Measuring the parameter indicative of a temperature of the first zone may comprise measurement of a current in the first heating element, measuring a temperature of the first heating element using a temperature sensor 31a, 131a and / or measuring a temperature of the first zone using a first temperature sensor 31a, 131a. The temperature sensor may be any 15 temperature sensor described herein. The first zone may be an inlet zone 20a of the body 10 and the first heating element may be an inlet heating element 30a, 130a. The method may further comprise controlling the inlet heating element 30a, 130a to heat the inlet zone during an injection phase in which 20 the sample is injected into the sample injector. The method may further comprise measuring a second parameter indicative of a temperature of a second zone of the body and independently controlling a second heating element of the plurality of heating elements to heat the second zone to one or more 25 temperature setpoints. Measuring the parameter indicative of a temperature of the second zone may comprise measurement of a current in the second heating element, measuring a temperature of the second heating element using a second temperature sensor 31c, 131c, measuring a temperature of the second zone using a second temperature sensor 31c, 131c and / or measuring an oven temperature using a sensor. The second zone may be a 30 downstream zone 20c of the body 10 and the second heating element may be a downstream heating element 30c, 130c. The method may further comprise measuring a third parameter indicative of a temperature of a third zone of the body 10, 110, independently controlling a third heating element of the 35 plurality of heating elements to heat the third zone to one or more temperature setpoints. 10 07 25 Measuring the parameter indicative of a temperature of the third zone may comprise measurement of a current in the third heating element, measuring a temperature of the third heating element using a third temperature sensor 31b, 131b and / or measuring a temperature of the third zone using a third temperature sensor 31b, 131b. The third zone 5 may be an intermediate zone 20c of the body 10 and the third heating element may be an intermediate heating element 30c, 130c. In use, the plurality of heating elements may be controlled to maintain a predetermined temperature profile in one or more of the zones of the body 10, 110 as external conditions 10 vary. For example, when the temperature of the oven of the gas chromatograph is increased and there is heat transfer from the oven of the gas chromatograph to an adjacent zone (i.e. a downstream zone 20c) of the injector, the corresponding heating element may be controlled to reduce the temperature of that heating element and thereby maintain a temperature setpoint in that zone of the body 10. Optionally, the heating element may be 15 controlled based at least in part on an output of a sensor configured to measure the internal temperature of the oven. The plurality of heating elements may also be controlled according to a timed program in which temperature setpoints are set for each heating element in each of a plurality of 20 phases of operation of the sample injector 1, 101. The phases of operation of the sample injector may be as follows: - The “stand by” phase, in which the gas chromatography system is idle and some operational parameters may differ from sample injection and analysis setpoints; - The “ready” phase, in which method parameters for the gas chromatography 25 system are set. Once these parameters are reached, the gas chromatography system is ready for operation. - The “injection” phase, in which the sample is physically introduced into the sample injector. - The “evaporation” phase, in which the sample is evaporated and is transferred by 30 carrier gas into the gas chromatography column. The “injection” and “evaporation” phases may be separate sequential phases. Alternatively, “injection” and “evaporation” phases may overlap or may be simultaneous. - The “GC run” phase, in which the sample passes through the column for chromatographic separation. This phase is defined herein with reference to the 35 heating element temperature settings. The skilled person will understand that the 10 07 25 sample may begin to pass through the column for chromatographic separation during the evaporation phase. - The “post run” phase in which the gas chromatography system is restoring the initial operational parameters. 5 In any embodiment of the present disclosure, one or more of the plurality of heating elements may be controlled to heat the corresponding zones of the body to one or more temperature setpoints (i.e. target temperatures) during each phase of operation. The one or more temperature setpoints may vary between samples. The temperature setpoints may be 10 set based on being: - at or above a predetermined temperature for a high temperature setpoint; or - at or below a predetermined temperature for a low temperature setpoint. The predetermined temperature may be determined based on the composition of the 15 sample mixture, solvent or injector components. For example, it may be a boiling point temperature, or temperature suitable for full evaporation, of one of the sample, a sample component or a solvent which is combined with the sample for injection into the injector. For example, a “low temperature setpoint” may be defined as a setpoint below the boiling point of the solvent or below the boiling point of the sample mixture. In the hot needle 20 technique the low temperature setpoint may be selected as a temperature that minimizes off gassing of siloxanes from the septum, for example a temperature setpoint at or below 100 degrees C. A “high temperature setpoint” may be defined as a temperature sufficiently high for a full evaporation of the sample. The high temperature setpoint may be a temperature sufficiently high for a full evaporation of the sample within a reasonable 25 amount of time. The high temperature setpoint may be above the solvent boiling point or the sample mixture boiling point. The high temperature setpoint may be below the boiling point of some components of the sample if the components can fully evaporate below their boiling point in a reasonable amount of time. A reasonable amount of time may be a time period which does not significantly extend the usual run time for a gas chromatograph 30 and / or a time period that does not impact the separation efficiency required for the analysis of the sample, as these would be understood by the skilled person. This is typically of the order of a few minutes, such as less than 5 minutes, less than 3 minutes, less than 1 minute, or 1 to 3 minutes. For the injectors described herein having either a PTV or SSL injector, this may typically be 1 to 3 minutes. 10 07 25 The following provides non-limiting examples as to how the sample injector of the present disclosure may be controlled in use. In a first example, the sample injector is a PTV injector, for example as in the embodiment 5 shown in Figures 2 and 3. The injector operates in a programmed temperature mode, controlling the plurality of heating elements to heat the corresponding zones of the body 10 to one or more temperature setpoints during each phase of operation as shown in Table 1 below. In the following “T setpoint” is the “temperature setpoint”. 10 As shown in Table 1, during the injection phase each of the plurality of heating elements may be controlled such that the zones 20a, 20b, 20c of the body 10 are kept at a low temperature setpoint in order to avoid any evaporation during the injection (to thereby avoid sample discrimination). After the injection of the sample 45 (see Figure 1) into the injector 1, 101 is completed, an intermediate heating element of the plurality of heating elements 15 may be heated to the high temperature setpoint in order to completely evaporate the sample and allow its transfer to the analytical column in the sample evaporation phase. Once the sample 45 has been transferred to the column 43, the inlet zone 20a can be cooled down by not heating the inlet heating element 30a, 130a in order to preserve the septum from the degradation caused by the high temperatures (thereby reducing in this 20 way the release of siloxanes, which may be present in the material of the septum 40, into the analytical system). 10 07 25 Table 1: Temperature set points for the inlet, intermediate and downstream zones for a PTV injector Stand by Ready Injection Evaporation GC Run Post Run Inlet zone 20a Low T setpoint Low T setpoint Low T setpoint High T setpoint Not heated Low T setpoint Intermediate zone 20b Low T setpoint Low T setpoint Low T setpoint High T setpoint High T setpoint Low T setpoint Downstream zone 20c Low T setpoint Low T setpoint Low T setpoint High T setpoint High T setpoint or not heated, dependent on oven temperature Low T setpoint 5 The downstream zone 20c of the injector 1,101 may also be cooled down, or be allowed to cool, by not heating the downstream heating element 30c, 130c, in order to preserve the adjacent part of the GC column 43 (part of which is received inside the injector) from overheating, as this part of the injector is indirectly heated also by the GC oven 41. The intermediate zone of the injector can be kept at high temperature during the GC run 10 phase in order to allow for bake out of a liner 11 a of the sample chamber 11 (i.e. heating of the liner 11a in the absence of a sample 45 in order to eliminate residuals) thereby reducing the carryover effect (contamination from residuals of previously run samples) without compromising the inlet zone 20a and the septum 50, and / or the downstream zone 20c and the upper part of the GC column 43. 15 In embodiments in which the sample injector 1,101 is an SSL injector, the plurality of zones may comprise an inlet zone 20a and the plurality of heating elements may comprise an inlet heating element 30a, 130a arranged to heat the inlet zone 20a. In such embodiments, the sample injector 1, 101 may be operated according to a “cold needle technique” or a “hot needle technique” for introduction of the sample into the sample 10 07 25 injector 1, 101. In the cold needle technique, a sample 45 is introduced to the injector 1, 101 as a liquid band and evaporation of the sample 45 takes place once the sample is inside the sample chamber. For this technique the temperature of a syringe needle used to introduce the sample 45 to the injector 1,101 must remain below the solvent boiling point 5 temperature during the injection of the sample 45 into the injector 1,101 and therefore the inlet zone 20a of the injector 1,101 must be kept at low temperature. In the hot needle technique, the inlet zone 20a of the injector is heated to a high temperature setpoint sufficiently high for a full evaporation of the sample, and the sample is injected into the injector as a thermospray (i.e. the injection and evaporation phases are overlapping or 10 simultaneous). In a second and third examples described below the sample injector is an SSL injector, for example the sample injector 101 as in the embodiment shown in Figures 4 and 5. The plurality of heating elements 130a, 130b, 130c are configured and controlled to heat the corresponding zones 20a, 20b, 20c of the body 10 to one or more temperature setpoints 15 during each phase of operation as described below. In the second example, the sample injector 101 may be operated using the cold needle technique, wherein the temperature setpoints of each of the plurality of zones of the body 10 are maintained throughout the process as follows: 20 - Inlet zone 20a - low temperature setpoint; - Intermediate zone 20b - high temperature setpoint; and - Downstream zone 20c - high temperature setpoint. In the third example, the sample injector 101 may be operated using the hot needle 25 technique, wherein the temperature setpoints of each of the plurality of zones may all be kept at the high temperature setpoint or may be controlled in a timed mode as shown in Table 2 below. In both techniques, the intermediate heating element 130b and downstream heating 30 element 130c may be maintained at the high temperature setpoint throughout. In the hot needle technique, in the injection / sample evaporation phase the inlet heating element 30a, 130a heats the inlet zone 20a to a hight temperature setpoint sufficiently high for a full evaporation of the sample. The injection and evaporation phases may therefore be overlapping or simultaneous. The inlet heating element 30a, 130a may heat the inlet zone 20a to the high temperature setpoint for a predetermined period, until the sample transfer is complete. The predetermined period may be approximately in the range of 0.5-5 minutes. Table 2: Temperature set points for the inlet, intermediate and downstream zones for a 5 SSL injector using hot needle injection 10 07 25 Stand by Ready Injection and Evaporation GC Run Post Run Inlet zone 20a Low T setpoint High T setpoint High T setpoint High T for a predetermined time period and then Low T setpoint Low T setpoint Intermediate Zone 20b High T setpoint High T setpoint High T setpoint High T setpoint High T setpoint Downstream zone 20c High T setpoint High T setpoint High T setpoint High T setpoint High T setpoint As the inlet heating element 30a, 130a may be controlled (for example, by a controller 44 (see Figure 1) of the sample injector or gas chromatograph) to selectively heat the inlet zone 20a to the high temperature setpoint or the low temperature setpoint, the same 10 sample injector can be selectively used for either the cold needle technique or the hot needle technique. As the temperature setpoint of the inlet zone 20a may be reduced shortly after the injection phase, the sample injector 1, 101 of the present disclosure also avoids the drawback of the hot needle injectors that keep the inlet zone 20a constantly heated. Continuous high temperatures in the inlet zone 20a may result in degradation of the 15 material of the septum 50, which may cause contamination of the system by siloxanes from the septum material. While embodiments of the present disclosure have been described above and illustrated in the drawings, these are for example only and are non-limiting. It will be appreciated by those skilled in the art that alternatives are possible within the ambit of the disclosure. For 20 example, the sample injector, gas chromatograph and method of the present disclosure may comprise any combination of the following features. 10 07 25 The body of the sample injector may be generally elongate and define a longitudinal axis. The plurality of heating elements may be arranged in series along the body, such that there is no overlap of the heating elements along a longitudinal axis of the body. Alternatively, an end portion of one or more of the heating elements may overlap with an end portion of an 5 adjacent heating element of the plurality of heating elements. In the illustrated examples, the sample injector comprises three heating elements. In any embodiment of the disclosure, the sample injector may comprise two or more heating elements, or at least three heating elements. For example, the sample injector may 10 comprise only a inlet heating element and a downstream heating element. Alternatively, the sample injector may comprise a inlet heating element, a downstream heating element and one or more intermediate heating elements, i.e. the plurality of zones may include any number of intermediate zones, each provided with a corresponding heating element of the plurality of heating elements. 15 The inlet zone may be the part of the body distal to the gas chromatograph in use. The downstream zone may be the part of the body proximal to the gas chromatograph in use. The intermediate zone may be defined as any portion of the body between the inlet and downstream zones. 20 In embodiments of the present disclosure, each heating element of the plurality of heating elements is configured to heat a single corresponding zone of the plurality of zones (i.e. a zone which is different to that heated by any other of the plurality of heating elements). Each of the plurality of heating elements is configured such that a temperature of each 25 heating element is controllable independently of the temperature of any and all others of the plurality of heating elements. However, in use, any two or more of the plurality of heating elements may controlled such that their temperatures are the same. The heating elements may be in the form of heating coils arranged around the body of the 30 injector, such that the zone of the body to be heated is arranged inside the coil heating that zone, or alternatively, each of the plurality of heating elements may be in the form of a resistor arranged adjacent to the corresponding zone of the body to be heated. The resistor may be in the form of a cartridge or cylinder. 10 07 25 In any embodiment in which the heating elements are heatable coils, the coil density of the heatable coils may be uniform or, alternatively, a coil density of one or more heating elements may vary along a length of the body (e.g. in a direction generally aligned with the longitudinal axis of the body). For example, the coil density may be higher in the inlet 5 heating element than in the downstream heating element, to allow for increased heating to compensate for the relatively lower surrounding temperature of the inlet zone, being arranged furthest from the oven. The heating elements may be formed from a metallic material such as a metal alloy, for 10 example an Fe-Cr-AI alloy. The body may be formed from stainless steel and may comprise a glass or metal liner arranged to line the sample chamber. Each of the plurality of heating elements may be of a uniform length (e.g. a length relative to a longitudinal axis of the body). Alternatively, one or more of the heating elements may 15 have different lengths to the other(s) of the plurality of heating elements. For example, the plurality of heating elements may comprise: - an inlet heating element extending longitudinally along approximately a quarter of body of the injector; - one or more intermediate heating elements may extend longitudinally along 20 approximately half of body of the injector; and / or - a downstream heating element extending longitudinally along approximately a quarter of body of the injector. In any embodiment, the sample may be a liquid, solid or gaseous sample. The sample may 25 be a sample mixture. In use, the sample is typically combined with a liquid solvent for injection into the sample injector. The sample injector may comprise a controller configured to measure the parameter indicative of a temperature of a zone of the plurality of zones of the body and to derive a 30 temperature of that zone based on the parameter. The parameter may be, for example, a current applied to the corresponding heating element, an input from a temperature sensor arranged adjacent to that zone of the body or an input from a temperature sensor arranged adjacent to the heating element. The controller may control the heating element corresponding to that zone, for example by controlling the current applied to the heating 35 element, based on the derived temperature. 10 07 25 Each temperature sensor may be arranged outside the body and adjacent to, optionally in contact with, the corresponding zone of the body (i.e. the zone whose temperature is to be determined based on that sensor). 5 The sample injector of the illustrated embodiments is described as being a PTV or SSL injector. These injector types are shown by way of example and are non-limiting. In any embodiment, in particular with any control method or program as described above, any type of injector may be used. For example, a multimode injector may be used. 10 The plurality of heating elements may be heated by current passing through the heating elements, regulated by voltage control. In a direct heating technique a correlation between the current and the temperature of the heating element can be obtained for each heating element by means of a calibration. In this case the temperature is not directly measured, 15 but derived from the current used. Alternatively, control of the temperature of each heating element may be carried out by measuring the temperature of the corresponding zone of the body by means of a temperature sensor. The injector heater is heated by current circulation, but the control of the current therein is performed based on the feedback of the temperature measured by the temperature sensor. 20 Forced air cooling apparatus may be provided around the injector body to allow further control of the temperature of the injector. The high temperature setpoint may be in the range of 180 to 350 degrees Celsius. For 25 example, for an SSL injector, the high temperature setpoints may be between 180 and 320 degrees Celsius and / or for an PTV injector, the high temperature setpoint may be between 280 and 350 degrees Celsius. The low temperature setpoint may be under 100 degrees Celsius. 30 The sample injector may be configured to heat one of the plurality of heating elements to a different temperature than the other or others of the plurality of heating elements for at least one phase of operation of the sample injector. The sample injector may comprise a controller configured to control the heating elements in this way. 10 07 25 As described herein, each heating element of the plurality of heating elements is configured to heat a different zone of the plurality of zones. The terms “corresponding zone” and “corresponding heating element” are used herein to refer to the zone that a particular heating element is configured to heat and, conversely, the heating element which heats a 5 particular zone. A heating element may be configured to heat a corresponding zone of the plurality of zones by arranging the heating element around or adjacent to the corresponding zone. As used herein, reference to heating a zone “during” a particular phase of operation refers 10 to heating that zone throughout the phase described, unless otherwise specified. The sample injector may comprise a septum arranged at the inlet end of the body for receiving the sample therethrough. A septum cap may be arranged at the inlet end for connection of the sample chamber to a sample purge line, splitting line, carrier gas inlet 15 and / or similar connections. A downstream end of the sample injector may comprise an injection portion to be received in the oven in use. Any embodiment of the sample injector according to the present invention may be provided as part of a gas chromatograph. Any sample injector of the present disclosure may be 20 configured to carry out the method according to the present disclosure, for example the sample injector may comprise a controller configured to control the heating elements according to a method according to the present disclosure. In any embodiment, the gas chromatograph or sample injector may comprise a controller 25 configured to carry out the methods described herein. By independently controlling the temperature of a plurality of heating elements, each arranged to heat a corresponding zone of the injector body, the temperature of each zone of body can be more precisely controlled, allowing varied heating of the different zones 30 such that, for example, cold spots and overheated areas in the body, and therefore in the sample chamber defined by the body, can be avoided. Controlling the heating elements individually means that the temperature of each different zone of the body, and therefore of the sample chamber defined by the body, can be 35 controlled precisely and in a manner that varies between the zones. This allows the 10 07 25 controller to compensate for the temperature variations and make the temperature to be as uniform as possible to avoid cold spots or overheated regions. For example, the upstream end of the injector can be set to a lower temperature to avoid heating of the septum. Independent control of the temperature of the downstream end also avoids overheating of 5 the top part of the analytical column of the oven, which is heated both by the injector and the oven. By using heating elements in the form of heating coils, contact between the heating element and the body can be improved, thereby improving efficiency of heat transfer from 10 the heating element to the body. By providing a casing surrounding one or more of the heating elements, more uniform heating may be provided due to the mass and conductivity of the material of the casing. For example, the casing may be a metal block, such as an aluminium block. 15 Providing a plurality of individually controlled heating elements in an SSL injector for a gas chromatograph also allows a single injector to provide both cold needle and hot needle injection, eliminating the need to change between types of injector when switching between these methods, thereby reducing downtime in the use of the oven and reducing the amount 20 of equipment required to carry out the methods. Also, the present invention also avoids the drawback of the hot needle injectors, which typically keep the inlet zone constantly heated, producing septum degradation and system contamination by siloxanes, as the top part of the injector can be cooled down just after the injection phase as evaporation of the solvent from the needle has already been completed. 25 10 07 25

Claims

1. A sample injector for a gas chromatograph comprising:a body defining a sample chamber configured to receive a sample; and5 a plurality of heating elements for heating the body;wherein each heating element of the plurality of heating elements is configured to be controlled independently of each other heating element of the plurality of heating elements;wherein:10 the body is an elongate tube defining a longitudinal axis, the body having an inletend and a downstream end, the downstream end being distal to the inlet end along the longitudinal axis;the body comprises a plurality of zones, the plurality of zones comprising an inlet zone arranged at or proximal to the inlet end of the body, a downstream zone arranged at 15 or proximal to the downstream end of the body, and an intermediate zone arranged between the inlet zone and the downstream zone; andthe plurality of heating elements is configured such that each heating element of the plurality of heating elements is configured to heat a different zone of the plurality of zones, the plurality of heating elements comprising:20 an inlet heating element arranged to heat the inlet zone;a downstream heating element arranged to heat the downstream zone; and one or more intermediate heating elements arranged to heat theintermediate zone.25 2. The sample injector of claim 1 wherein the sample injector is configured to heat oneof the plurality of zones to a different temperature than the other or others of the plurality of zones during at least one phase of operation of the sample injector.

3. The sample injector of claim 1 or claim 2 wherein the sample injector is configured30 to vary the temperature of at least one zone of the plurality of zones during at least one phase of operation of the sample injector.

4. The sample injector of any preceding claim wherein the plurality of heating elements are arranged in series along the body.10 07 255. The sample injector of any preceding claim wherein each heating element of the plurality of heating elements is arranged adjacent to or around a corresponding zone of the plurality of zones.5 6. The sample injector of claim 5 wherein each heating element of the plurality ofheating elements comprises a heatable coil arranged around the body;wherein optionally a coil density of one or more heating elements of the plurality of heating elements varies along a length of the body.10 7. The sample injector of claim 5 further comprising a plurality of casings, each of theplurality of casings being arranged around one of the plurality of heating elements and a corresponding zone of the plurality of zones;wherein optionally the plurality of casings are arranged in series along the body.15 8. The sample injector of any preceding claim further comprising a controller, thecontroller being configured to independently control each heating element of the plurality of heating elements based on a parameter indicative of a temperature of the zone of the plurality of zones that the heating element is configured to heat.20 9. The sample injector of any preceding claim further comprising a plurality oftemperature sensors, each of the plurality of temperature sensors being arranged adjacent to a zone of the plurality of zones.

10. The sample injector of claim 9 as dependent on claim 8, wherein the parameter25 indicative of a temperature of the zone comprises one or more of:a current in the heating element;a temperature of the heating element measured using a corresponding temperature sensor of the plurality of temperature sensors; anda temperature of the zone measured using a corresponding temperature sensor of 30 the plurality of temperature sensors.

11. The sample injector of any preceding claim wherein each heating element of the plurality of heating elements is configured to be energised independently of each other heating element of the plurality of heating elements.10 07 2512. A method of heating a sample injector for a gas chromatograph comprising: providing a plurality of heating elements configured to heat a body of the sample injector; andcontrolling each heating element of the plurality of heating elements5 independently of each other heating element of the plurality of heating elements;wherein the body comprises a plurality of zones, andwherein each heating element of the plurality of heating elements is configured to heat a different zone of the plurality of zones;the method further comprising:10 measuring a first parameter indicative of a temperature of an inlet zone ofthe plurality of zones, and controlling an inlet heating element of the plurality of heating elements to heat the inlet zone to one or more temperature setpoints;measuring a second parameter indicative of a temperature of a downstream zone of the plurality of zones, and independently controlling a downstream heating element15 of the plurality of heating elements to heat the downstream zone to within to one or more temperature setpoints; andmeasuring a third parameter indicative of a temperature of an intermediate zone of the plurality of zones, and independently controlling an intermediate heating element of the plurality of heating elements to heat the intermediate zone to one or more20 temperature setpoints.

13. The method of claim 12 further comprising varying the temperature of at least one zone of the plurality of zones during at least one phase of operation of the sample injector.25 14. The method of claim 12 or claim 13 further comprising heating one of the plurality ofzones to a different temperature than the other or others of the plurality of zones during at least one phase of operation of the sample injector.

15. The method of any one of claims 12 to 14 wherein measuring the parameter30 indicative of a temperature of the inlet zone comprises measurement of a current in the first heating element, measuring a temperature of the inlet heating element using a temperature sensor and / or measuring a temperature of the inlet zone using a temperature sensor.10 07 2516. The method of any one of claims 12 to 15 further comprising controlling the inlet heating element to heat the inlet zone during an injection phase in which the sample is introduced into the sample injector.5 17. The method of claim 16 further comprising either:i) selectively controlling the inlet heating element to heat the inlet zone during the injection phase to:a high temperature setpoint at which the sample can fully evaporate; or a low temperature setpoint;10 orii) controlling the inlet heating element to maintain the temperature of the inlet zone at the low temperature setpoint throughout operation of the sample injector.

18. The method of claim 16 further comprising:15 i) controlling the inlet heating element to heat the inlet zone to a high temperaturesetpoint at which the sample can fully evaporate during an injection phase in which the sample is introduced into the sample injector; andii) controlling the inlet heating element such that the temperature of the inlet zone is reduced from the high temperature setpoint to a low temperature setpoint.2019. The method of claim 18 wherein step ii) occurs either: immediately after an evaporation phase in which the sample is evaporated and is transferred by carrier gas into the gas chromatography column; orafter a predetermined period following completion of the evaporation phase. 2520. The method of any one of claims 12 to 19 wherein measuring the parameter indicative of a temperature of the downstream zone comprises measurement of a current in the downstream heating element, measuring a temperature of the downstream heating element using a sensor, measuring a temperature of the downstream zone using a sensor 30 and / or measurement of an oven temperature using a sensor.

21. The method of claim any one of claims 12 to 20wherein the downstream heating element is maintained at a high temperature setpoint at which the sample can fully evaporate throughout operation of the sample injector.10 07 2522. The method of any one of claims 12 to 21 wherein measuring the parameter indicative of a temperature of the intermediate zone comprises measurement of a current in the intermediate heating element, measuring a temperature of the intermediate heating element using a sensor and / or measuring a temperature of the intermediate zone using a 5 sensor.

23. The method of any one of claims 12 to 22wherein the intermediate heating element is maintained at a high temperature setpoint at which the sample can fully evaporate throughout operation of the sample 10 injector.

24. The method of any of claims 12 to 23 further comprising: initially controlling the plurality of heating elements to heat each zone of the plurality of zones to a low temperature setpoint; and15 after the sample has been introduced to the sample injector, controlling the pluralityof heating elements to heat each zone of the plurality of zones to a high temperature setpoint at which the sample can fully evaporate until the sample has evaporated.

25. The method of claim 24 further comprising:20 controlling an intermediate heating element of the plurality of heating elements toheat an intermediate zone of the plurality of zones to a high temperature setpoint during a gas chromatograph run phase following evaporation of the sample; and / orcontrolling an inlet heating element of the plurality of heating elements such that an inlet zone of the plurality of zones is not heated during the gas chromatograph run phase.2526. The method of claim 24 or claim 25 further comprising measuring a parameter indicative of an oven temperature of the gas chromatograph and, depending on the measured parameter either:controlling a downstream heating element of the plurality of heating elements to 30 heat a downstream zone of the plurality of zones to a high temperature setpoint during a gas chromatograph run phase following evaporation of the sample; orcontrolling the downstream heating element of the plurality of heating elements such that a downstream zone of the plurality of zones is not heated during the gas chromatograph run phase.LO CXI27. The method of any of claims 12 to 26 wherein the sample injector is a sample injector according to any of claims 1 to 11.

28. A gas chromatograph assembly comprising a sample injector as claimed in any of 5 claims 1 to 11.

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