Flow splitter for gas chromatography systems

Abstract

The analytical instrument assembly includes a gas chromatograph, a first detector, a second detector, and a pneumatic control module. The gas chromatograph includes a flow splitter configured to receive a sample. The first detector is coupled to the flow splitter. The second detector is coupled to the flow splitter. The pneumatic control module is coupled to the flow splitter and configured to deliver a carrier gas to the flow splitter. The flow splitter is configured to split the sample and deliver at least a first portion of the sample to the first detector and deliver at least a second portion of the sample to the second detector at a first split ratio. The pneumatic control module is configured to deliver one of (i) a make-up flow including a third portion of the carrier gas to the flow splitter, or (ii) an exhaust flow from the flow splitter, and the pneumatic control module is configured to adjust the pressure in the flow splitter, thereby maintaining the first split ratio at a substantially constant value.

Description

[Technical field]

[0001] The present disclosure relates to a flow splitter for a gas chromatography system.

[0002] Gas chromatography (GC) is traditionally used to separate and analyze compounds (e.g., volatile organic compounds (VOCs)) in a variety of applications and across several fields. Traditional gas chromatography may involve combining a sample or mixture of analytes to be analyzed with a carrier gas (e.g., helium or hydrogen) in a column to form an eluent. As the eluent travels through the column, the various analytes may be separated from one another due to various factors such as, for example, flow characteristics, mass of the analytes, etc. Upon exiting the column, the signals of the separated analytes may be detected and recorded.

[0003] When two or more analytes of a sample have similar properties, it can be difficult to separate such analytes, as they may tend to migrate at similar rates through the column such that a sufficient amount of separation does not occur. To address the foregoing and improve the resolution of the analysis, rather than using a single column, techniques have been implemented in which at least a portion of the eluate is periodically injected into a second column, whereby the second column may have one or more properties different from the first column, and the eluate is detected by a detector at the end of the second column. This is commonly known as multidimensional (or comprehensive two-dimensional) gas chromatography (GC×GC).

[0004] GC-MS / FID and GCxGC-MS / FID instruments (GC and GCxGC with dual mass spectrometry (MS) and flame ionization detection (FID) as detectors) use gas chromatography to separate mixtures into their individual components and then use mass spectrometry and flame ionization detection to identify and quantify each component, respectively.

[0005] Current flow splitters in gas chromatography (e.g., GC-MS / FID and GC×GC-MS / FID) are generally either simple tees (passive splitters) or flow splitters with a make-up stream (active splitters). In some implementations, flow splitters based on Deans switches may be implemented. Depending on the conditions and configuration, these splitters may not necessarily provide a constant split stream / split ratio to the FID and / or may not be easy to configure or operate.

[0006] Different conditions (column flow rates, split ratios, etc.) generally require different restrictors (transfer lines) from the flow splitter to the detector. Such implementation requires that the restrictors be physically switched to meet the desired conditions. Having to change the restrictor every time a different condition is desired can be time consuming, laborious, and inefficient. Therefore, it may be desirable to implement a GC system that can meet a variety of different conditions without the need to change the restrictor.

[0007] This section provides background information related to the present disclosure; background information is not necessarily prior art. Summary of the Invention [Means for solving the problem]

[0008] One aspect of the disclosure provides an analytical instrument assembly including a gas chromatograph, a mass spectrometer, a flame ionization detector, and a pneumatic control module. The gas chromatograph includes a primary column configured to receive an eluate including a sample and a first portion of a carrier gas, and a flow splitter coupled to the primary column and configured to receive the eluate. The mass spectrometer is coupled to the flow splitter via a first restrictor. The flame ionization detector is coupled to the flow splitter via a second restrictor. The pneumatic control module is coupled to the flow splitter and configured to deliver a second portion of the carrier gas to the flow splitter configured to split the eluate at a first split ratio and deliver at least a first portion of the eluate through the first restrictor to the mass spectrometer and deliver at least a second portion of the eluate through the second restrictor to the flame ionization detector. The pneumatic control module is configured to deliver one of (i) a make-up flow including a third portion of the carrier gas to the flow splitter, or (ii) an exhaust flow from the flow splitter, and the pneumatic control module is configured to adjust the pressure in the flow splitter, thereby maintaining the first split ratio at a substantially constant value.

[0009] Implementations of the present disclosure may include one or more of the following features: In some implementations, the split ratio is defined as the flow to the flame ionization detector divided by the flow to the mass spectrometer at the point where the flow splitter splits the flow.

[0010] The flow splitter may be configured to maintain the first split ratio substantially constant throughout the course of a temperature programmed gas chromatography analysis.

[0011] The pneumatic control module may be configured to control exhaust flow from the flow splitter, thereby back-regulating pressure within the flow splitter.

[0012] The gas chromatograph may include a secondary column coupled to the primary column and configured to receive the eluent. The gas chromatograph may include a modulator between the primary and secondary columns.

[0013] The regulated pressure and the second portion of the carrier gas may be configured to control the amount of the second portion of the eluate delivered to the flame ionization detector. The first portion of the eluate delivered to the mass spectrometer may be diluted with make-up gas. The first portion of the eluate delivered to the mass spectrometer may be split such that at least a portion of the first portion of the eluate is vented.

[0014] The regulated pressure and the second portion of the carrier gas may be configured to control the amount of the first portion of the eluent that is delivered to the mass spectrometer.

[0015] The eluent may be configured to be delivered at a constant flow rate from the primary column to the flow splitter, and the pneumatic control module is configured to deliver a second portion of the carrier gas to the flow splitter at a constant flow rate and mix the eluent with the second portion of the carrier gas, and to deliver the second portion of the eluent to the flame ionization detector at a constant flow rate throughout the course of the temperature programmed gas chromatography analysis.

[0016] Another aspect of the present disclosure provides an analytical instrument assembly including a gas chromatograph, a first detector, a second detector, and a pneumatic control module. The gas chromatograph includes a flow splitter configured to receive a sample. The first detector is coupled to the flow splitter. The second detector is coupled to the flow splitter. The pneumatic control module is coupled to the flow splitter and configured to deliver a carrier gas to the flow splitter. The flow splitter is configured to split the sample and deliver at least a first portion of the sample to the first detector and at least a second portion of the sample to the second detector at a first split ratio. The pneumatic control module is configured to deliver one of (i) a make-up flow including a third portion of the carrier gas to the flow splitter, or (ii) an exhaust flow from the flow splitter, and the pneumatic control module is configured to adjust the pressure in the flow splitter, thereby maintaining the first split ratio at a substantially constant value.

[0017] Implementations of the present disclosure may include one or more of the following features: In some implementations, the first detector is a mass spectrometer. The second detector may be a flame ionization detector.

[0018] The gas chromatograph may include an inlet and a primary column coupled to the inlet, the inlet configured to provide the sample and a first portion of the carrier gas to the primary column. A split ratio may be defined as the flow to the second detector divided by the flow to the first detector at the point where the flow splitter splits the flow. The gas chromatograph may include a secondary column coupled to the primary column and configured to receive the sample, and a modulator between the primary and secondary columns.

[0019] The flow splitter may be configured to maintain the first split ratio at a substantially constant value throughout the course of a temperature programmed gas chromatography analysis.

[0020] The pneumatic control module may be configured to control exhaust flow from the flow splitter, thereby back-regulating the pressure within the flow splitter.

[0021] The regulated pressure and carrier gas may be configured to control the amount of the second portion of the sample that is delivered to the second detector.

[0022] The regulated pressure and carrier gas may be configured to control the amount of the first portion of the sample that is delivered to the first detector.

[0023] Another aspect of the disclosure provides a flow splitter for splitting a column eluate to two detectors with a constant split ratio at the split point (representative sampling), but with dilution and / or additional splitting of the eluate stream for reasons of flow control throughout the temperature programmed GC separation. Overall, the splitter is configured to perform representative sampling to obtain accurate quantification. Representative sampling means that the relative amounts of analytes in the mixture separated during the temperature programmed GC separation are the same before and after the split, i.e., a constant split ratio throughout the temperature programmed GC separation. The split portion of the first detector is representative, while the split portion of the second detector may or may not be representative, depending on the type of detector. The split portion going to the second detector is representative at the split point, but due to pressure and flow control, the eluate split to the second detector is variably diluted or further variably split. This variable dilution or splitting may make the response of the second detector non-representative. Whether the sampling to the second detector is representative depends on the type of detector and its control. Generally, the variability in sampling to the second detector, when present, is not a large percentage of the sample volume. The system may be utilized for GC-MS / FID and GC×GC-MS / FID, with the FID providing quantitative accuracy as the first detector and the MS providing at least qualitative characteristics as the second detector. The system design and controls are configured to provide easy installation and operation, and to allow variable column flows and split ratios with a single set of restrictors for the first and second detectors.

[0024] The details of one or more implementations of the disclosure are set forth in the accompanying drawings and the description below. Other aspects, features, and advantages will be apparent from the description and drawings, and from the claims. [Brief description of the drawings]

[0025] [Figure 1]FIG. 1 is a schematic diagram of an exemplary GC-MS / FID system including a flow splitter according to the principles of the present disclosure.

[0026] [Diagram 2] FIG. 2 is a schematic diagram of an exemplary GC×GC-MS / FID system including the flow splitter of FIG. 1 in accordance with the principles of the present disclosure.

[0027] [Figure 3A] FIG. 2 is a schematic diagram of a first exemplary flow splitter of FIG. 1.

[0028] [Figure 3B] FIG. 2 is a schematic diagram of a second exemplary flow splitter of FIG. 1.

[0029] [Figure 3C] FIG. 2 is a schematic diagram of a third exemplary flow splitter of FIG. 1.

[0030] [Figure 3D] FIG. 2 is a schematic diagram of a fourth exemplary flow splitter of FIG. 1.

[0031] [Figure 3E] FIG. 2 is a schematic diagram of a fifth exemplary flow splitter of FIG. 1.

[0032] [Figure 3F] FIG. 2 is a schematic diagram of a sixth exemplary flow splitter of FIG. 1.

[0033] [Figure 4] FIG. 2 is a perspective view of the flow splitter of FIG. 1.

[0034] [Diagram 5] 5 is a cross-sectional view of the flow splitter of FIG. 1 taken along line 5-5 of FIG. 4.

[0035] [Figure 6] FIG. 6 is a cross-sectional view of a first Tee of the flow splitter of FIG. 5.

[0036] [Figure 7] FIG. 6 is a cross-sectional view of a second Tee of the flow splitter of FIG. 5.

[0037] [Figure 8] FIG. 6 is a cross-sectional view of a third Tee of the flow splitter of FIG. 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] Like reference numbers in the various drawings indicate like elements.

[0039] Next, the exemplary configurations will be described more fully with reference to the accompanying drawings. The exemplary configurations are provided so that the disclosure is thorough and fully conveys the scope of the disclosure to those skilled in the art. Specific details, such as examples of specific components, devices, and methods, are described to provide a thorough understanding of the disclosed configurations. It will be apparent to those skilled in the art that specific details need not be used, that the exemplary configurations may be embodied in many different forms, and that the specific details and the exemplary configurations should not be interpreted as limiting the scope of the disclosure.

[0040] 1 and 2, an analytical instrument assembly 10 is generally shown. The assembly 10 can include a gas chromatography device, which can be a gas chromatograph (GC) 12a as shown in FIG. 1, or a comprehensive two-dimensional (multi-dimensional) gas chromatograph (GC×GC) 12b as shown in FIG. 2. As will become apparent, the principles of the present disclosure can be applied to the GC 12a, GC×GC 12b, and / or any other suitable gas chromatography device, including but not limited to gas-liquid chromatography (GLC), gas-solid chromatography (GSC), and the like. The assembly 10 includes a first detector, i.e., a mass spectrometer (MS) 14 coupled to the gas chromatography device 12a, 12b, a second detector, i.e., a flame ionization detector (FID) 16 coupled to the gas chromatography device 12a, 12b, and a pneumatic control module (PCM) 18.

[0041] Although the assembly 10 has been described as including an MS 14 as a first detector and an FID 16 as a second detector, it is understood that the first and second detectors may include any suitable detectors, such as a thermal conductivity detector (TCD), an alkaline flame detector (AFD), a catalytic combustion detector (CCD), a discharge ionization detector (DID), a polyarc reactor, a flame photometric detector (FPD), an atomic emission detector (AED), an electron capture detector (ECD), a nitrogen phosphorus detector (NPD), a dry electrolytic conductivity detector (DELCD), a vacuum ultraviolet (VUV), a Hall electrolytic conductivity detector (ElCD), a helium ionization detector (HID), an infrared detector (IRD), a photoionization detector (PID), a pulsed discharge ionization detector (PDD), a thermal ionization detector (TID), etc. It is further understood that any of the aforementioned detectors may be arranged in any suitable combination.

[0042] 1 and 2, the gas chromatography devices 12a, 12b include a main oven 20, an inlet 22, a primary column 24, and a flow splitter 26. With the exception of the GC×GC 12b, which includes a secondary column 28 and a modulator 30, the GC 12a and the GC×GC 12b, including the components and their functions, may be substantially similar or the same, as shown in FIG. 2 and as described in more detail below. Thus, it should be understood that the following description applies to both the GC 12a and the GC×GC 12b, with the exception of the secondary column 28 and the modulator 30, which apply only to the GC×GC 12b.

[0043] The main oven 20 can house or receive at least an inlet 22, a primary column 24, a flow splitter 26, a secondary column 28, and a modulator 30. The inlet 22 can be configured to produce an eluate 32 including a sample 34 (i.e., eluate), and a first portion or stream 36a of a carrier gas (i.e., eluent). The sample 34 can be injected into the inlet 22 via an injection device, such as a syringe, an automatic injection device, or any other suitable means, and can be any suitable sample or analyte, such as petroleum, fragrances, drug-related liquids, and the like. The first portion 36a of the carrier gas can be contained in a tank and can be any suitable gas, such as an inert gas such as helium, a non-reactive gas such as nitrogen, and the like. The first portion 36a of the carrier gas can be supplied to the inlet 22 in a constant stream, and the sample 34 can be supplied to the inlet as an aliquot. The inlet 22 can mix the sample 34 with a first portion 36 a of the carrier gas to form an eluate 32 , and the inlet 22 can inject the eluate 32 into the primary column 24 .

[0044] The primary column 24 and the secondary column 28 may each be wound in a generally circular configuration or may each have any suitable configuration. For the GC 12a, the primary column 24 may extend from the inlet 22 to the flow splitter 26. For the GC×GC 12b, the primary column 24 may extend from the inlet 22 to the modulator 30, and the secondary column 28 may extend from the modulator 30 to the flow splitter 26. In some implementations, the primary column 24 and the secondary column 28 may have different characteristics from one another. In one example, the primary column 24 may be longer, have a larger diameter, and / or include a different stationary phase than the secondary column 28. In another example, the primary column 24 may have a smaller diameter than the secondary column 28.

[0045] For GC×GC 12b, the modulator 30 may be configured to receive the eluate 32 from the primary column 24 and perform modulation on the eluate 32 over a period of time called a modulation period. The modulation process may include at least the steps of sampling the eluate 32 and injecting all or a portion of the eluate 32 into the secondary column 28. In some implementations, the modulation process includes the additional step of collecting the eluate 34 before injecting it into the secondary column 28. The modulation period is the time it takes the modulator 30 to complete the modulation process, including the steps described above.

[0046] The MS 14 may be coupled to the gas chromatography devices 12a, 12b via a transfer line 38. The MS 14 and FID 16 may each be configured to receive an eluent 32 containing a sample 34 and detect or collect a plurality of data about the sample 34 including, for example, retention time, signal (or intensity), etc. Although the MS 14 and FID 16 are described herein, it should be understood that any suitable detector may be implemented including, but not limited to, an electron capture detector (ECD), an atomic emission detector (AED), a sulfur chemiluminescence detector (SCD), a nitrogen chemiluminescence detector (NCD), a nitrogen phosphorus detector (NPD), etc.

[0047] The computing device can communicate with the MS 14 and the FID 16 and can receive, analyze, and / or process data about the sample 34 from the MS 14 and the FID 16. The computing device can be any suitable device, such as, for example, a computer, laptop, tablet, smartphone, etc. The computing device can process the data about the sample 34 and output a chromatogram. The computing device can be used to program or control any suitable components of the assembly 10, including the PCM 18, the modulator 30, etc.

[0048] 1-3E, the MS 14 may be coupled to the flow splitter 26 via a mass spectrometer (MS) restrictor 40 extending to or through the transfer line 38. The FID 16 may be coupled to the flow splitter 26 via a flame ionization detector (FID) restrictor 42. The PCM 18 may be coupled to the flow splitter 26 via a flow control capillary 44 and a make-up / exhaust flow capillary 46. The MS restrictor 40 is configured to receive the first portion 32a of the eluate and deliver the first portion 32a of the eluate to the MS 14. The FID restrictor 42 is configured to receive the second portion 32b of the eluate and deliver the second portion 32b of the eluate to the FID 16. The flow control capillary 44 is configured to deliver a second portion 36b of the carrier gas to the flow splitter 26, and the make-up / exhaust flow capillary 46 delivers a third portion (or make-up flow) 36c of the carrier gas to the flow splitter 26 or an exhaust flow 37 from the flow splitter 26. of As shown in the figure, the flow of eluent 32, which includes sample 34 and portions 36a-36c of carrier gas, is generally represented by FX, e.g., the flow of sample 34 is F 34 It is represented by:

[0049] 3A and 4-6, the flow splitter 26 can include a first Tee 48, a second Tee 50, a third Tee 52, and one or more connecting tubes 54 connecting the first Tee 48 to the second Tee 50 and the second Tee 50 to the third Tee 52. In some implementations, the connecting tube 54 can be a single component extending from the first Tee 48 through the second Tee 50 to the third Tee 52 with appropriate holes to facilitate the flow of the eluent 32 and the eluent 36. Although three Tee's 48, 50, 52 are shown in FIG. 3A, it should be understood that the Tee's 48, 50, 52 can be combined or connected in any suitable manner. For example, as shown in FIG. 3C, the second Tee 50 and the third Tee 52 can be combined into a single fitting. Similarly, as shown in Figure 3D, the second tee 50 and the third tee 52 may be combined into a single joint 50 that is generally cross-shaped. As yet another example, as shown in Figure 3E, the tee 48, 50, 52 may all be combined with one another to form a single joint. Although not shown, it should be understood that the first tee 48 and the second tee 50 may similarly be combined into a single joint. The configuration shown in Figures 3A-3E may have the advantage of reduced dead volume and therefore better chromatographic peak shape.

[0050] 3B, for each of the coupling configurations, the locations of the first detector 14 and the second detector 16 may not be equivalent in terms of the quantitative response of each detector relative to the unsplit response of the detector, depending on the type of detector (flux-sensitive, concentration-sensitive, or other). At the location of the first detector 14, the diluted eluate or column flow F 32 is split directly to the first detector restrictor 40, and the flow to the first detector 14 is the column flow F 32 is constant, and the flow F of the second portion 36b of the carrier gas is 36bis constant when the pressure is properly controlled (programmed) over the course of the chromatographic separation. In this position (first detector 14), most GC detectors respond quantitatively in the same way as in the single detector case, and the column flow F 32 100% with a reduced response consistent with the split ratio and dilution.

[0051] At the location of the second detector 16, the split flow to the second detector 16 is also constant at the split point (i.e., the tip of the first detector restrictor 40), but with forward / forward pressure adjustment, the split flow is mixed with the make-up flow F before entering the second detector restrictor 42. 36c With back pressure regulation, the split flow of the second detector 16 is split again before entering the second detector restrictor 42, and the remainder of the flow split to the second detector 16 is diluted with the exhaust F 37 In either case of pressure regulation, when the pressure is controlled to provide an appropriate pressure for the desired flow that maintains a constant split ratio at the split point throughout the chromatographic separation, the flow to the second detector 16 will vary somewhat (approximately (+ / - 5%) up to 20% depending on conditions and restrictors) over the course of a temperature programmed GC separation.

[0052] Unlike the first detector 14, the response of the second detector 16 relative to its response as a single detector depends on the type of GC detector and whether the splitter is in forward pressure regulation or back pressure regulation. Due to either dilution (forward pressure regulation) or further splitting (back pressure regulation), the quantitative response of the second detector 16 may not be consistent with the unsplit response, i.e., the quantitative response of the second detector 16 may change over the course of the chromatographic separation relative to the unsplit case. For example, if the second detector 16 is an FID (flux sensitive), the back pressure regulation variably ejects a portion of the split sample, and therefore the response of the FID 16 does not match the unsplit case. However, in the case of forward pressure regulation, the sample is diluted, but the entire split sample is transferred to the FID 16, and therefore the response of the FID 16 is the same as long as the other flows of the FID 16 (i.e., fuel, make-up, air) are properly controlled. If the second detector 16 is a concentration-sensitive GC detector, then upon backpressure adjustment, the concentration is expected to remain unchanged and the response to be essentially the same as in the unsplit case.

[0053] 3A, the first Tee 48 may include a first opening 48a, a second opening 48b opposite the first opening 48a, and an intermediate opening 48c between the first opening 48a and the second opening 48b. Similarly, the second Tee 50 may include a first opening 50a, a second opening 50b opposite the first opening 50a, and an intermediate opening 50c between the first opening 50a and the second opening 50b. Similarly, the third Tee 52 may include a first opening 52a, a second opening 52b opposite the first opening 52a, and an intermediate opening 52c between the first opening 52a and the second opening 52b. Alternatively, the Tee 48, 50, 52 may have any suitable configuration. 3D , the fitting 50 may include a third opening 50c and a fourth opening 50d. One of the connecting tubes 54 may extend from the second opening 48b of the first Tee 48 to the first opening 50a of the second Tee 50, and the other of the connecting tubes 54 may extend from the second opening 50b of the second Tee 50 to the first opening 52a of the third Tee 52.

[0054] With reference to Figure 6, the first tee 48 can include a first compression fitting 49a at or near the first opening 48a, a second compression fitting 49b at or near the second opening 48b, and a third compression fitting 49c at or near the third opening 48c. With reference to Figure 7, the second tee 50 can include a first compression fitting 51a at or near the first opening 50a, a second compression fitting 51b at or near the second opening 50b, and a third compression fitting 51c at or near the third opening 50c. With reference to Figure 8, the third tee 52 can include a first compression fitting 53a at or near the first opening 52a, a second compression fitting 53b at or near the second opening 52b, and a third compression fitting 53c at or near the third opening 52c.

[0055] Referring to FIG. 3A, the first opening 48a of the first Tee 48 can receive the primary column 24 for the GC 12a (or the secondary column 28 for the GC×GC 12b), and the column 24, 28 can extend through the first opening 48a and the second opening 48b and terminate at a tip 56 beyond the second opening 48b in the connecting tube 54. The middle opening 48c of the first Tee 48 can receive the flow control capillary 44 of the PCM 18. The first compression fitting 49a can sufficiently seal the first opening 48a such that the second portion 36b of the carrier gas can only flow from left to right as shown in FIG. 6. Specifically, the second portion 36b of the carrier gas can flow around the outside of the column in an annulus between the column (inside) and the connecting tube 54 (outside).

[0056] The FID restrictor 42 may extend through the second opening 52b of the third Tee 52, through the first opening 52a of the third Tee 52, through the second opening 50b of the second Tee 50, through the first opening 50a of the second Tee 50, and may terminate at a tip 58 in a connecting tube 54 downstream from the columns 24, 28. The middle opening 50c of the second Tee 50 may receive the MS restrictor 40, and the middle opening 52c of the third Tee 52 may receive the make-up / exhaust flow capillary 46 of the PCM 18.

[0057] As another example, as shown in FIG. 3B , the MS restrictor 40 can extend through a second opening 52b of a third Tee 52, through a first opening 52a of the third Tee 52, through a second opening 50b of a second Tee 50, through a first opening 50a of the second Tee 50, and can terminate at a tip 60 in a connecting tube 54 downstream from the columns 24, 28, and an intermediate opening 50c of the second Tee 50 can accept the FID restrictor 42.

[0058] Referring to FIG. 3A, the flow control capillary 44 of the PCM 18 controls the constant flow F of the second portion 36b of the carrier gas as determined by the PCM 18. 36bThe second portion 36b of the carrier gas is delivered by a flow F 36b The effluent or column flow F from the columns 24, 28 passes through the first Tee 48 and through the annulus around the columns 24, 28. 32 and the flow F of the second portion 36b of the carrier gas. 36b The flow F mixes in the connecting tube 54 before reaching the tip 58 of the FID restrictor 42. The length of the connecting tube 54 between the first tee 48 and the second tee 50 is 32 , F 36b may be long enough for mixing.

[0059] With continued reference to FIG. 3A, effluent stream F 32 The split point of the eluent 32 is at or near the tip 58 of the FID restrictor 42 between the first tee 48 and the second tee 50 in the connecting tube 54. The eluent 32 is split at the split point, with a second portion 32b of the eluent being delivered to the FID restrictor 42 and the FID 16, and the remainder of the eluent 32, i.e., the first portion 32a of the eluent, flowing around the FID restrictor 42 and through the intermediate tee 50 where it is coupled to a make-up flow F of carrier gas 36c. 36c In the case of backpressure regulation, the eluate 32a is mixed with the exhaust stream F 37 and a portion that reaches the MS restrictor 40 as the third portion 32c of the eluate. 32c is sent to the MS restrictor 40 and to the MS 14. The second compression fitting 53b can sufficiently seal the second opening 52b such that the third portion 36c of the carrier gas can only flow from right to left as shown in FIG. 8. Specifically, the third portion 36c of the carrier gas can flow around the outside of the column in an annulus between the column (inside) and the connecting tube 54 (outside). Because the sample 34 passes by the outside of the FID restrictor 42, the FID restrictor 42 can be formed of a metal capillary tube that is coated with an inert material on both the inside and outside to minimize adsorption.

[0060] The make-up / exhaust flow capillary 46 of the PCM 18 couples the make-up flow F entering the flow splitter 26.36c The pressure in the connecting tube 54 can be adjusted using a pressure regulator 56. The desired pressure may be programmed on the PCM 18. This pressure may be the inlet pressure to the FID restrictor 42, and the flow through the FID restrictor 42 can be defined based on the inlet pressure, the outlet pressure (atmospheric or any other suitable pressure), the dimensions of the FID restrictor 42, and the temperature zone of the FID restrictor 42. This controlled pressure in the flow splitter 26 can also define the outlet pressure of the columns 24, 28, which means that the inlet pressures of the columns 24, 28 will result in a constant eluate flow F from the columns 24, 28. 32 The constant eluate flow F from the columns 24, 28 can be programmed. 32 to the flow splitter 26, and a constant flow F of the second portion 36b of the carrier gas 36b is the eluate flow rate F 32 When mixed with the sample 34, a constant flow F of the sample 34 to the tip 58 of the FID restrictor 42 is 34 may be provided.

[0061] In some implementations, the PCM 18 may be configured to split the flow F of FIG. 3A out of the flow splitter 26. 37 The exhaust flow F exiting the flow splitter 26 is shown by the arrows 37 can be used to regulate the pressure in the connecting tube 54. In such an implementation, the pressure regulation is back pressure instead of forward pressure regulation, and the flow F of the first portion 32a of the eluate 32a is the flow F of the third portion 32c of the eluate 32c The other part is the exhaust flow F 37 It is.

[0062] Constant flow F of sample 34 34 is a constant flow F of the first portion 34a of the sample into the FID restrictor 42. 34a and a constant flow F of the second portion 34b of the sample around the outside of the FID restrictor 42. 34b In this process, the sample stream F from columns 24, 28 can be split into 34 is the flow F of the second portion 36b of the carrier gas 36bHowever, in some implementations, the FID 16 is a flux-based detector, and therefore the response of the FID 16 may be the same as for an undiluted sample. 36c is the flow F of the second portion 36b of the carrier gas 36b In some configurations, the flow F of the first portion 32a of the eluent at the split point (tip 58 of the FID restrictor 42) can be adjusted accordingly based on 32a may also be constant.

[0063] supply flow F 36c or exhaust flow F 37 By controlling the PCM pressure regulation, the PCM 18 may be able to vary the column flow rate and split ratio using the same set of restrictors for the MS 14 and FID 16 (i.e., MS restrictor 40 and FID restrictor 42). This simplifies the use of the flow splitter 26 by reducing or eliminating the need to change restrictors for different conditions. Furthermore, by controlling the pressure in the flow splitter 26, the PCM 18 can appropriately control the inlet pressure to the restrictor and the outlet pressure of the column to maintain a constant split ratio throughout the course of a temperature programmed GC analysis. In some implementations, the split ratio may be defined as the flow to the FID 16 divided by the flow to the MS 14 at the point where the flow splitter 26 splits the flow. The adjusted pressure and make-up flow F 36c or exhaust flow F 37 is configured to provide different split ratios at different column flow rates and temperatures using the same MS restrictor 40 and FID restrictor 42 and appropriately low regulated pressures.

[0064] In one implementation, the effluent flow F 32 The flow of the second portion 36b of the carrier gas F can flow at 0.5 to 20 mL / min. 36b can flow at 1 to 20 mL / min, and a make-up flow of carrier gas 36c, F 36ccan flow at 0.1 to 0.3 mL / min at a forward pressure of 1 to 5 psig (approximately 6.895 to 34.475 kPa (psig is gauge pressure, the same below)), and the flow F of the third portion 32c of the eluate 32c can flow at 1-1.5 mL / min.

[0065] 3B, the operation of the flow splitter 26 may be substantially similar to that shown in FIG. 3A, except that the make-up flow F 36c The regulated pressure from the flow F of the first portion 32a of the eluent in the MS restrictor 40 32a The division of the eluate 32 can be controlled by controlling the flow F of the remainder of the eluate 32, i.e., the second portion 32b of the eluate. 32b is the make-up flow of carrier gas 36c, F 36c The fourth portion 32d of the eluate may be delivered to the FID 16. In this configuration, the make-up flow F 36c can vary during the course of the temperature programmed separation, which is reflected by the flow F of the second portion 32b of the eluate. 32b When added to the second portion 32b of the eluate and the make-up flow F to the FID 16, 36c In some implementations, the make-up flow (when helium carrier gas) or fuel gas (when hydrogen carrier gas) that is part of the FID 16 and not the splitter 26 can be programmed to maintain an overall constant flow to the FID 16 (the FID make-up flow or fuel flow, plus the flow from the splitter to the FID).

[0066] With reference to FIG. 3F, this configuration may be similar to the Deans switch configuration described as a splitter. The main difference is the flow and pressure control. Splitting is controlled with an incoming constant flow and pressure regulation (forward pressure or back pressure). The resulting splitter has some of the same properties as the configurations of FIG. 3A-E, but the performance differs in some respects. Depending on the type of detector being split, one configuration may be preferred over the other. The configuration of FIG. 3F may also be configured with fittings, where the column and detector restrictors are inserted through the fittings. Such a connection may have the advantage of reduced dead volume and therefore better chromatographic peak shape. Reduced dead volume may be particularly beneficial for the narrow chromatographic peaks of GCxGC.

[0067] In the above configuration, the incoming flow F of the second portion 36b of the carrier gas 36b makes the first detector restrictor 40 a variable restrictor. 36b and the column flow F by controlling the PCM pressure regulation. 32 And the split ratio can be changed using the same set of restrictors for the first and second detectors. This simplifies the use of the splitter by reducing or eliminating the need to change restrictors for different conditions. Furthermore, by controlling the pressure in the splitter, the inlet pressure to the restrictor and the outlet pressure of the column are appropriately controlled to maintain a constant split ratio.

[0068] Due to the large difference in sensitivity between MS and FID, the split flow from the column can be very small, making it difficult to control such a small flow. The present invention dilutes the sample so that the split flow to the MS is larger and more easily controlled, but since the FID is a flux-sensitive detector, the dilution of the sample does not affect the sensitivity of the FID.

[0069] In addition to those mentioned above, the systems and methods described herein may provide the following advantages: (i) a constant split ratio to the FID throughout the entire chromatographic separation; (ii) only a pair of restrictors (for the MS and FID) is sufficient for a range of operating conditions (column flow rate, split ratio) and restrictor calculations and modifications are not required as with some other flow modulators; (iii) the only operator inputs required are basic chromatographic parameters (column flow rate, split ratio, temperature conditions, column dimensions); (iv) the operating pressure at the flow splitter is near atmospheric pressure (approximately 1-5 psig (approximately 6.895 to 34.475 kPa)) over the range of column flows and split ratios that enable the fastest possible chromatography upstream of the flow splitter; (v) the column flow and FID split flow are operated in constant flow mode; (vi) the MS and FID peak retention times can be adjusted by a simple constant offset and proportionality factor; and (vii) the tip of the column and restrictors and flows are configured to minimize dead volume.

[0070] The terminology used herein is merely for the purpose of describing certain exemplary configurations and is not intended to be limiting. As used herein, the singular articles "a," "an," and "the" may be intended to include the plural unless the context clearly indicates otherwise. The terms "comprises," "comprising," "including," and "having" are inclusive and thus specify the presence of features, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof. The steps, processes, and operations of the methods described herein should not be construed as necessarily requiring their execution in the particular order described or illustrated, unless specifically identified as an order of execution. Additional or alternative steps may be employed.

[0071] When an element or layer is referred to as "on," "engaged to," "connected to," "attached to," or "coupled to" another element or layer, it may be directly on, engaged with, connected to, attached to, or coupled to the other element or layer, or there may be intervening elements or layers. In contrast, when an element is referred to as "directly on," "directly engaged to," "directly connected to," "directly attached to," or "directly coupled to" another element or layer, there may not be intervening elements or layers. Other words used to describe relationships between elements (e.g., "between" and "directly between," "adjacent" and "directly adjacent," etc.) should be interpreted in the same manner. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0072] Terms such as first, second, third, etc. may be used herein to describe various elements, components, regions, layers, and / or sections. These elements, components, regions, layers, and / or sections should not be limited by these terms. These terms may only be used to distinguish one element, component, region, layer, or section from another region, layer, or section. Terms such as "first", "second", and other number terms do not imply an order or sequence unless clearly indicated by the context. Thus, a first element, component, region, layer, or section described below may be referred to as a second element, component, region, layer, or section without departing from the teachings of the example configuration.

[0073] An embodiment of the present invention is, for example, as follows. [Example 1] In analytical instrument assembly, 1. A gas chromatograph comprising: a primary column configured to receive an eluate comprising the sample and a first portion of the carrier gas; a flow splitter coupled to the primary column and configured to receive the eluate; A gas chromatograph comprising: a mass spectrometer coupled to the flow splitter via a first restrictor; a flame ionization detector coupled to the flow splitter through a second restrictor; a pneumatic control module coupled to the flow splitter, delivering a second portion of the carrier gas to the flow splitter configured to split the eluate at a first split ratio, delivering at least a first portion of the eluate through the first restrictor to the mass spectrometer and delivering at least a second portion of the eluate through the second restrictor to the flame ionization detector; a pneumatic control module configured to deliver one of (i) a make-up flow comprising a third portion of the carrier gas to the flow splitter, or (ii) an exhaust flow from the flow splitter, the pneumatic control module configured to adjust a pressure within the flow splitter, thereby maintaining the first split ratio at a substantially constant value; An analytical instrument assembly comprising: [Example 2] 2. The analytical instrument assembly of claim 1, wherein the split ratio is defined as the flow to the flame ionization detector divided by the flow to the mass spectrometer at the point where the flow splitter splits the flow. [Example 3] 2. The analytical instrument assembly of claim 1, wherein the flow splitter is configured to maintain the first split ratio at the substantially constant value throughout the course of a temperature programmed gas chromatography analysis. [Example 4] 2. The analytical instrument assembly of example 1, wherein the pneumatic control module is configured to control exhaust flow from the flow splitter, thereby backpressure regulating the pressure within the flow splitter. [Example 5] 2. The analytical instrument assembly of claim 1, wherein the gas chromatograph includes a secondary column coupled to the primary column and configured to receive the eluate. [Example 6] 6. The analytical instrument assembly of claim 5, wherein the gas chromatograph includes a modulator between the primary column and the secondary column. [Example 7] 2. The analytical instrument assembly of claim 1, wherein the regulated pressure and the second portion of the carrier gas are configured to control an amount of the second portion of the eluent delivered to the flame ionization detector. [Example 8] 8. The analytical instrument assembly of example 7, wherein the first portion of the eluate delivered to the mass spectrometer is diluted with a make-up gas. [Example 9] 2. The analytical instrument assembly of claim 1, wherein the regulated pressure and the second portion of the carrier gas are configured to control the amount of the first portion of the eluent delivered to the mass spectrometer. [Example 10] 2. The analytical instrument assembly of claim 1, wherein the eluent is configured to be delivered from the primary column to the flow splitter at a constant flow rate, and the pneumatic control module is configured to deliver the second portion of the carrier gas to the flow splitter at a constant flow rate, mix the eluent with the second portion of the carrier gas, and deliver the second portion of the eluent to the flame ionization detector at a constant flow rate throughout the course of a temperature programmed gas chromatography analysis. [Example 11] In analytical instrument assembly, a gas chromatograph including a flow splitter configured to receive the sample; a first detector coupled to the flow splitter; a second detector coupled to the flow splitter; a pneumatic control module coupled to the flow splitter, delivering a carrier gas to the flow splitter configured to split the sample at a first split ratio and deliver at least a first portion of the sample to the first detector and at least a second portion of the sample to the second detector; a pneumatic control module configured to deliver one of (i) a make-up flow comprising a third portion of the carrier gas to the flow splitter, or (ii) an exhaust flow from the flow splitter, the pneumatic control module configured to adjust a pressure within the flow splitter, thereby maintaining the first split ratio at a substantially constant value; An analytical instrument assembly comprising: [Example 12] 12. The analytical instrument assembly of claim 11, wherein the first detector is a mass spectrometer. [Example 13] 12. The analytical instrument assembly of claim 11, wherein the second detector is a flame ionization detector. [Example 14] 12. The analytical instrument assembly of claim 11, wherein the gas chromatograph includes an inlet and a primary column coupled to the inlet, the inlet configured to provide the sample and a first portion of the carrier gas to the primary column. [Example 15] 15. The analytical instrument assembly of claim 14, wherein the split ratio is defined as the flow to the second detector divided by the flow to the first detector at the point where the flow splitter splits the flow. [Example 16] 15. The analytical instrument assembly of claim 14, wherein the gas chromatograph includes a secondary column coupled to the primary column and configured to receive the sample, and a modulator between the primary column and the secondary column. [Example 17] 12. The analytical instrument assembly of claim 11, wherein the flow splitter is configured to maintain the first split ratio at the substantially constant value throughout the course of a temperature programmed gas chromatography analysis. [Example 18] 12. The analytical instrument assembly of claim 11, wherein the pneumatic control module is configured to control exhaust flow from the flow splitter, thereby backpressure regulating the pressure within the flow splitter. [Example 19] 12. The analytical instrument assembly of claim 11, wherein the regulated pressure and the carrier gas are configured to control the amount of the second portion of the sample delivered to the second detector. [Example 20] 12. The analytical instrument assembly of claim 11, wherein the regulated pressure and the carrier gas are configured to control the amount of the first portion of the sample delivered to the first detector. Although several implementations have been described, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.

Claims

1. In analytical instrument assembly, 1. A gas chromatograph comprising: a primary column configured to receive an eluate comprising the sample and a first portion of the carrier gas; a flow splitter coupled to the primary column and configured to receive the eluate; A gas chromatograph comprising: a mass spectrometer coupled to the flow splitter via a first restrictor; a flame ionization detector coupled to the flow splitter through a second restrictor; a pneumatic control module coupled to the flow splitter, delivering a second portion of the carrier gas to the flow splitter configured to split the eluate at a first split ratio and deliver at least a first portion of the eluate through the first restrictor to the mass spectrometer and deliver at least a second portion of the eluate through the second restrictor to the flame ionization detector; delivering a make-up flow comprising a third portion of the carrier gas to the flow splitter; Delivering the exhaust flow from the flow splitter; and a pneumatic control module configured to adjust a pressure in the flow splitter thereby delivering one of the make-up stream or the exhaust stream to maintain the first split ratio at a substantially constant value; An analytical instrument assembly comprising:

2. 2. The analytical instrument assembly of claim 1, wherein the split ratio is defined as the flow to the flame ionization detector divided by the flow to the mass spectrometer at the point where the flow splitter splits the flow.

3. 2. The analytical instrument assembly of claim 1, wherein the flow splitter is configured to maintain the first split ratio at the substantially constant value throughout the course of a temperature programmed gas chromatography analysis.

4. 2. The analytical instrument assembly of claim 1, wherein the pneumatic control module is configured to control exhaust flow from the flow splitter, thereby back-pressure regulating the pressure within the flow splitter.

5. The analytical instrument assembly of claim 1 , wherein the gas chromatograph includes a secondary column coupled to the primary column and configured to receive the eluate.

6. 6. The analytical instrument assembly of claim 5, wherein the gas chromatograph includes a modulator between the primary column and the secondary column.

7. 2. The analytical instrument assembly of claim 1, wherein the regulated pressure and the second portion of the carrier gas are configured to control an amount of the second portion of the eluent delivered to the flame ionization detector.

8. 8. The analytical instrument assembly of claim 7, wherein the first portion of the eluate delivered to the mass spectrometer is diluted with a make-up gas.

9. 2. The analytical instrument assembly of claim 1, wherein the regulated pressure and the second portion of the carrier gas are configured to control an amount of the first portion of the eluent delivered to the mass spectrometer.

10. 2. The analytical instrument assembly of claim 1, wherein the eluent is configured to be delivered from the primary column to the flow splitter at a constant flow rate, and the pneumatic control module is configured to deliver the second portion of the carrier gas to the flow splitter at a constant flow rate, mix the eluent with the second portion of the carrier gas, and deliver the second portion of the eluent to the flame ionization detector at a constant flow rate throughout the course of a temperature programmed gas chromatography analysis.

11. In analytical instrument assembly, a gas chromatograph including a flow splitter configured to receive the sample; a first detector coupled to the flow splitter; a second detector coupled to the flow splitter; a pneumatic control module coupled to the flow splitter, delivering a carrier gas to the flow splitter configured to split the sample at a first split ratio and deliver at least a first portion of the sample to the first detector and at least a second portion of the sample to the second detector; delivering a make-up flow comprising a third portion of the carrier gas to the flow splitter; Delivering the exhaust flow from the flow splitter; and a pneumatic control module configured to adjust a pressure in the flow splitter thereby delivering one of the make-up stream or the exhaust stream to maintain the first split ratio at a substantially constant value; An analytical instrument assembly comprising:

12. The analytical instrument assembly of claim 11 , wherein the first detector is a mass spectrometer.

13. 12. The analytical instrument assembly of claim 11, wherein the second detector is a flame ionization detector.

14. 12. The analytical instrument assembly of claim 11, wherein the gas chromatograph includes an inlet and a primary column coupled to the inlet, the inlet configured to provide the sample and a first portion of the carrier gas to the primary column.

15. 15. The analytical instrument assembly of claim 14, wherein the split ratio is defined as the flow to the second detector divided by the flow to the first detector at the point where the flow splitter splits the flow.

16. 15. The analytical instrument assembly of claim 14, wherein the gas chromatograph includes a secondary column coupled to the primary column and configured to receive the sample, and a modulator between the primary column and the secondary column.

17. 12. The analytical instrument assembly of claim 11, wherein the flow splitter is configured to maintain the first split ratio at the substantially constant value throughout the course of a temperature programmed gas chromatography analysis.

18. 12. The analytical instrument assembly of claim 11, wherein the pneumatic control module is configured to control exhaust flow from the flow splitter, thereby back-pressure regulating the pressure within the flow splitter.

19. The analytical instrument assembly of claim 11 , wherein the regulated pressure and the carrier gas are configured to control an amount of the second portion of the sample that is delivered to the second detector.

20. The analytical instrument assembly of claim 11 , wherein the regulated pressure and the carrier gas are configured to control an amount of the first portion of the sample that is delivered to the first detector.

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