Carrier gas ion scavenger to reduce peak trailing and reaction

Abstract

A method of reducing peak trailing and reactions when using a carrier gas that is not helium for gas chromatography-mass spectrometry (GC-MS) includes separating compounds using a gas chromatography column that uses a carrier gas that is not helium; providing the column output to an ionization chamber of a mass spectrometer; providing a scavenger gas to an ionization chamber of the mass spectrometer; ionizing the compound in the presence of the carrier gas and the scavenger gas; the ionized compounds are analyzed using a mass spectrometer.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of the prior-filed provisional application serial number US63 / 589,389, filed on October 11, 2023, and entitled “CARRIER GASION SCAVENGER TO REDUCE PEAK TAILING AND REACTIONS”, the contents of which are incorporated herein by reference in their entirety. Technical Field

[0003] The present disclosure relates generally to the field of mass spectrometry including carrier gas ion scavengers to reduce peak tailing and reactions. Background Art

[0004] Helium is considered the best gas chromatography (GC) carrier gas for gas chromatography-mass spectrometry (GC-MS). Helium is inert and has a very low electron ionization (EI) cross section, which results in less space charge in the ion source. Helium is often the carrier gas of choice due to sensitivity, efficiency, chemical inertness, safety or other considerations. In addition, the purity of the carrier gas flowing into the analytical column is critical to data quality. Helium, especially high-purity helium, is becoming increasingly expensive and difficult to purchase in some parts of the world. In addition, helium is non-renewable because it escapes into space due to its low mass.

[0005] Therefore, it is desirable to replace helium as a carrier gas.From the foregoing, it should be appreciated that a need exists for improved systems and methods that can utilize carrier gases other than helium. Summary of the invention

[0006] In a first aspect, a system for performing gas chromatography-mass spectrometry (GC-MS) analysis using a carrier gas other than helium includes a gas chromatograph including an inlet and a gas chromatograph column; a carrier gas source connected to the inlet of the gas chromatograph; a mass spectrometer including an ionization chamber and a mass analyzer, the ionization chamber being fluidically connected to the gas chromatograph column; and a scavenger gas supply for providing a scavenger gas to the ionization chamber.

[0007] In various embodiments of the first aspect, the scavenger gas has a lower ionization energy than the carrier gas.

[0008] In various embodiments of the first aspect, the scavenger gas is methane.

[0009] In various embodiments of the first aspect, the scavenger gas comprises two or more gas species. In a particular embodiment, each of the scavenger gas species has a lower ionization energy than the carrier gas. In a particular embodiment, the scavenger gas comprises methane and ammonia, such as a methane / ammonia mixture having an ammonia concentration between about 1% and about 10%.

[0010] In various embodiments of the first aspect, the carrier gas is nitrogen.

[0011] In various embodiments of the first aspect, the carrier gas is hydrogen.

[0012] A method for reducing peak tailing and reactions when a carrier gas other than helium is used for gas chromatography-mass spectrometry (GC-MS) analysis includes separating compounds using a gas chromatography column that uses a carrier gas other than helium; providing the column output to an ionization chamber of a mass spectrometer; providing a scavenger gas to the ionization chamber of the mass spectrometer; ionizing the compounds in the presence of the carrier gas and the scavenger gas; and analyzing the ionized compounds using the mass spectrometer.

[0013] In various embodiments of the second aspect, the scavenger gas has a lower ionization energy than the carrier gas.

[0014] In various embodiments of the second aspect, the scavenger gas is methane.

[0015] In various embodiments of the second aspect, the scavenger gas comprises two or more gas species. In a particular embodiment, each of the carrier gas species has a lower ionization energy than the carrier gas. In a particular embodiment, the scavenger gas comprises methane and ammonia, such as a mixture of methane and ammonia having an ammonia concentration between about 1% and about 10%.

[0016] In various embodiments of the second aspect, the carrier gas is nitrogen.

[0017] In various embodiments of the second aspect, the carrier gas is hydrogen. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] For a more complete understanding of the principles and advantages disclosed herein, reference is now made to the following description in conjunction with the accompanying drawings and figures, in which:

[0019] Figure 1 is a block diagram of an example mass spectrometry system according to various embodiments.

[0020] Figure 2A and Figure 2B are diagrams showing exemplary chromatograms of pesticide standards using helium as a carrier gas or using nitrogen as a carrier gas.

[0021] Figure 3Aand Figure 3B are graphs showing example mass spectra of deltamethrin when helium is used as a carrier gas or nitrogen is used as a carrier gas. Figure 3C is a diagram showing the mass spectrum of deltamethrin from the NIST library.

[0022] Figure 4A A flow chart is shown illustrating an exemplary method of using a scavenger gas and a carrier gas according to various embodiments.

[0023] Figure 4B A diagram illustrating an exemplary system using a scavenger gas and a carrier gas according to various embodiments.

[0024] Figure 5A , Figure 5B and Figure 5C is a graph showing an exemplary chromatogram of a pesticide standard mass spectrum of deltamethrin when nitrogen is used as a carrier gas together with a scavenger gas, according to various embodiments.

[0025] It should be understood that the drawings are not necessarily drawn to scale, nor are the relationships between objects in the drawings necessarily drawn to scale. The drawings are intended to be depictions of various embodiments of the devices, systems, and methods disclosed herein for clarification and understanding. Wherever possible, all drawings will use the same reference numerals to refer to the same or similar parts. In addition, it should be understood that the drawings are not intended to limit the scope of the present teachings in any way. DETAILED DESCRIPTION

[0026] Embodiments of systems and methods for using carrier gas ion scavengers to reduce peak tailing and reactions and increase response are described herein and in the accompanying exhibits.

[0027] The section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described in any way.

[0028] In the detailed description of various embodiments, for the purpose of explanation, many specific details are set forth to provide a thorough understanding of the disclosed embodiments. However, those skilled in the art will appreciate that these various embodiments may be practiced with or without these specific details. In other examples, structures and devices are shown in block diagram form. In addition, those skilled in the art can easily recognize that the specific order of presentation and execution methods is illustrative, and it is expected that the order may be varied and still remain within the spirit and scope of the various embodiments disclosed herein.

[0029] All literature and similar materials cited in this application, including but not limited to patents, patent applications, articles, books, treatises, and internet web pages, are expressly incorporated by reference in their entirety for any purpose. Unless otherwise described, all technical and scientific terms used herein have the meaning commonly understood by one of ordinary skill in the art to which the various embodiments described herein belong.

[0030] It should be understood that there is an implicit "about" before the temperature, concentration, time, pressure, flow rate, cross-sectional area, etc. discussed in the present teachings, so that there are slight and insubstantial deviations within the scope of the present teachings. In this application, unless otherwise specifically provided, the use of the singular includes the plural. In addition, the use of "comprising", "including" and "containing" is not intended to be limiting. It should be understood that both the foregoing general description and the following detailed description are exemplary and illustrative only, and are not limitations of the present teachings.

[0031] As used herein, "a" or "an" may also mean "at least one" or "one or more." In addition, the use of "or" is inclusive, such that the phrase "A or B" is true when "A" is true, "B" is true, or both "A" and "B" are true. In addition, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.

[0032] "System" describes a set of real or abstract components comprising a whole, in which each component interacts or relates to at least one other component within the whole.

[0033] Mass spectrometry platform

[0034] Various embodiments of the mass spectrometry platform 100 may include, for example, Figure 1 In various embodiments, Figure 1 The elements of may be incorporated into the mass spectrometry platform 100. According to various embodiments, the mass spectrometer 100 may include an ion source 102, a mass analyzer 104, an ion detector 106, and a controller 108.

[0035] In various embodiments, the ion source 102 generates a plurality of ions from the sample. The ion source may include, but is not limited to, a matrix-assisted laser desorption / ionization (MALDI) source, an electrospray ionization (ESI) source, an atmospheric pressure chemical ionization (APCI) source, an atmospheric pressure photoionization source (APPI), an inductively coupled plasma (ICP) source, an electron beam ionization source, a chemical ionization source, a photoionization source, a glow discharge ionization source, a thermal spray ionization source, and the like.

[0036] In various embodiments, the mass analyzer 104 may separate the ions based on their mass-to-charge ratio. For example, the mass analyzer 104 may include a quadrupole mass filter analyzer, a quadrupole ion trap analyzer, a time-of-flight (TOF) analyzer, an electrostatic trap (e.g., an orbital trap) mass analyzer, a Fourier transform ion cyclotron resonance (FT-ICR) mass analyzer, etc. In various embodiments, the mass analyzer 104 may also be configured to fragment the ions using collision induced dissociation (CID), electron transfer dissociation (ETD), electron capture dissociation (ECD), photoinduced dissociation (PID), surface induced dissociation (SID), etc., and further separate the fragmented ions based on the mass-to-charge ratio.

[0037] In various embodiments, the ion detector 106 can detect ions. For example, the ion detector 106 can include an electron multiplier, a Faraday cup, etc. The ions leaving the mass analyzer can be detected by the ion detector. In various embodiments, the ion detector can be quantitative so that the exact count of ions can be determined.

[0038] In various embodiments, the controller 108 can communicate with the ion source 102, the mass analyzer 104, and the ion detector 106. For example, the controller 108 can configure the ion source or enable / disable the ion source. In addition, the controller 108 can configure the mass analyzer 104 to select a specific mass range to be detected. In addition, the controller 108 can adjust the sensitivity of the ion detector 106, such as by adjusting the gain. In addition, the controller 108 can adjust the polarity of the ion detector 106 based on the polarity of the detected ions. For example, the ion detector 106 can be configured to detect positive ions or configured to detect negative ions.

[0039] Carrier gas

[0040] Helium is still considered the best gas chromatography (GC) carrier gas for GC-MS. It is inert and has a very low electron ionization (EI) cross section, which means less space charge in the ion source.

[0041] Hydrogen is cheap, easy to prepare, and leads to shorter separation times. However, it is flammable and causes peak tailing and reaction. Solutions to this include various surface coatings (see US 10,012,623, CPEssences; EP3,454,359, CPEssences; and US20210305036, Agilent). In addition, hydrogen can cause problems with maintaining a sufficiently high vacuum in a mass spectrometer system. The lower compression of the turbo pump for hydrogen can lead to unacceptable high pressure in the MS system or require larger or multiple vacuum pumps. This may be particularly problematic for ultra-high vacuum (UHV) MS systems.

[0042] Nitrogen is non-flammable, inexpensive, and easy to manufacture. It is also compatible with the vacuum pump systems used in MS systems. However, it also causes peak tailing (see Figure 2B ) and reactions (see Figure 3B ).

[0043] Figure 2A Shown is the chromatogram of the Restek GC Multi-Residue Pesticide Standard #6 using helium as carrier gas. Figure 2B The chromatogram of Restek GC multi-residue pesticide standard #6 using nitrogen as carrier gas is shown. Peak tailing can be observed when using nitrogen as carrier gas. In addition, the relative abundance of some compounds changes significantly when using nitrogen as carrier gas compared to helium.

[0044] Figure 3A shows the mass spectrum of deltamethrin using helium as carrier gas, Figure 3B Shown is the mass spectrum of deltamethrin using nitrogen as carrier gas. Figure 3C The mass spectrum of deltamethrin from the NIST library is shown. Compared with the mass spectra of 3A and 3C, Figure 3B Specifically, there are lower abundances of high m / z ions (e.g., m / z 253, 297), a much lower m / z 181, and in the case of helium ( Figure 3A ) or in the NIST library ( Figure 3C ) did not appear at m / z 195. Accurate mass analysis showed m / z 195 to be m / z 181 with an added nitrogen atom, probably due to a reaction with the nitrogen carrier gas.

[0045] Scavenger gas

[0046] In various embodiments, a scavenger gas may be added to reduce peak tailing and reactions caused by non-helium carrier gases. In various embodiments, the scavenger gas may include one or more gases or liquids. In a particular embodiment, at least one of the carrier gas species has a lower ionization energy than the carrier gas, such as all of the carrier gas species have a lower ionization energy than the carrier gas. In various embodiments, the lower ionization energy of the scavenger gas enables the scavenger gas to undergo charge exchange with the carrier gas ions generated in the ionization chamber, thereby reducing peak tailing and reactions between the carrier gas ions and the compound.

[0047] In addition, it may be advantageous for the scavenger to have a low ionization cross section to reduce the direct formation of scavenger gas ions. Table 1 shows the ionization energy (eV) and relative ionization cross sections of some of the various gases that can be used as scavenger gases. These scavenger gases have lower ionization energies than nitrogen (15.581 eV) and hydrogen (15.42593 eV).

[0048] Table 1. Possible scavenger gases

[0049]

[0050] In various embodiments, the scavenger gas may include methane, ammonia, isobutane, or any combination thereof. In certain embodiments, the scavenger gas may include a gas mixture, such as a mixture of methane and ammonia, for example, a mixture of methane and ammonia having an ammonia concentration between about 1% and about 10%.

[0051] Figure 4A 4 is a flow chart showing a method for using a scavenger gas to improve peak shape and reduce reactions when a carrier gas other than helium is used. At 402, a GC column can be used to separate compounds with a carrier gas other than helium. For example, the carrier gas can be hydrogen or nitrogen. At 404, the column output can be injected into an ionization chamber of a mass spectrometer.

[0052] At 406, a scavenger gas may be supplied to the ionization chamber. In various embodiments, the scavenger gas may be supplied directly into the ionization chamber. In other embodiments, the scavenger gas may be supplied to an area surrounding the ionization chamber and may diffuse into the ionization chamber. In other embodiments, the scavenger gas may be mixed with the output of the column before being supplied into the ionization chamber. In other embodiments, the scavenger gas may be mixed with a carrier gas before the GC column so that the column output contains the carrier gas together with the scavenger gas. In various embodiments, the scavenger gas may include methane, ammonia, isobutane, or any combination thereof.

[0053] At 408, the compound can be ionized in the presence of a carrier gas and a scavenger gas, and at 410, the ionized compound can be analyzed by mass spectrometry.

[0054] Figure 4B An exemplary GC-MS system 450 is shown that uses a scavenger gas to reduce tailing and reaction with a non-helium carrier gas. A carrier gas supply 452 can provide a flow of carrier gas to an inlet 454 of a gas chromatography system 456. In various embodiments, the carrier gas supply 452 can be a hydrogen supply, such as a hydrogen generator or a hydrogen cylinder. In other embodiments, the carrier gas supply 452 can be a nitrogen supply, such as a nitrogen cylinder or a nitrogen generator. In other embodiments, the carrier gas supply 452 can be a supply of any gas that is compatible with a gas chromatography other than helium.

[0055] A carrier gas may flow from the injection port 454 into the GC column 458. In various embodiments, the carrier gas may mix with compounds of the sample within the injection port 454 and carry the compounds into the GC column 458. The GC column 458 may be used to separate compounds in the sample based on interactions between the compounds and the stationary phase of the GC column 458. These interactions may result in different retention times for different compounds.

[0056] The output of the GC column 458 is fed into an ionization chamber 460 of a mass spectrometer 462. A scavenger gas supply 464 can supply scavenger gas into the ionization chamber. In various embodiments, the scavenger gas can include multiple scavenger gas species. The multiple scavenger gas species can be supplied premixed or can be supplied separately and mixed together when mixed with the carrier gas. In various embodiments, one or more scavenger gas species can be provided as a liquid that is volatilized prior to or while mixed with the carrier gas. Figure 4B In the embodiment shown, the scavenger gas may be injected directly into the ionization chamber 458. In other embodiments, the scavenger gas may be injected into the area adjacent to the ionization chamber 460 and diffuse into the ionization chamber 460. In other embodiments, the scavenger gas may be mixed with the carrier gas before the injection port 454, between the injection port 454 and the GC column 458, or after the GC column 458 and supplied to the ionization chamber 460 along with the carrier gas.

[0057] Ionization chamber 460 can ionize compounds, such as by electron ionization or chemical ionization. The ionized compounds can enter mass analyzer 466. Mass analyzer 466 can be a quadrupole mass filter analyzer, a quadrupole ion trap analyzer, a time of flight (TOF) analyzer, an electrostatic trap (e.g., an orbital trap) mass analyzer, a Fourier transform ion cyclotron resonance (FT-ICR) mass analyzer, other suitable mass analyzers, or any combination thereof. Mass analyzer 466 can analyze compounds to determine the mass-to-charge ratio (m / z) of the ionized compounds, the m / z ratio of the ion fragments produced by the ionized compounds, or any combination thereof.

[0058] Although the present teachings are described in conjunction with various embodiments, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives, modifications, and equivalents, as will be understood by those skilled in the art.

[0059] In addition, when describing various embodiments, the specification may have presented the method and / or process as a specific sequence of steps. However, insofar as the method or process does not rely on the specific order of the steps set forth herein, the method or process should not be limited to the specific sequence of steps described. As will be appreciated by those of ordinary skill in the art, other sequences of steps are also possible. Therefore, the specific order of the steps set forth in the specification should not be interpreted as a limitation on the claims. In addition, claims relating to the method and / or process should not be limited to performing their steps in the order written, and those skilled in the art can easily understand that the sequence can be varied and still remain within the spirit and scope of the various embodiments.

[0060] Example

[0061] Figure 5A Shown is the chromatogram of the Restek GC multi-residue pesticide standard #6 using nitrogen as carrier gas and 0.3 mL / min of methane added. Figure 5B Shown is the chromatogram of the Restek GC multi-residue pesticide standard #6 using nitrogen as carrier gas and 1.5 mL / min of methane added. Figure 5C The chromatogram of Restek GC multi-residue pesticide standard #6 using nitrogen as carrier gas and 1.5 mL / min of methane with 5% ammonia is shown. Figure 5A As shown in Figure 2, peak tailing and response can still be observed at lower amounts of methane. Increasing methane significantly reduces peak tailing and response, but results in a high baseline, as shown in Figure 2. Figure 5B As seen in Figure 5C As shown, the addition of 5% ammonia resulted in good peak shape, no response, and a lower baseline.

Claims

1. A system for performing gas chromatography-mass spectrometry (GC-MS) analysis using a carrier gas other than helium, the system comprising: A gas chromatograph, comprising an injection port and a gas chromatographic column; A carrier gas source, the carrier gas source being connected to an inlet of a gas chromatograph; a mass spectrometer comprising an ionization chamber and a mass analyzer, wherein the ionization chamber is fluidically coupled to the gas chromatography column; and A scavenger gas supply is used to provide scavenger gas to the ionization chamber.

2. The system of claim 1, wherein the scavenger gas has a lower ionization energy than the carrier gas.

3. The system of claim 1, wherein the scavenger gas is methane.

4. The system of claim 1, wherein the scavenger gas is isobutane.

5. The system of claim 1, wherein the scavenger gas comprises two or more gas species.

6. The system of claim 4, wherein each of the purge gas species has a lower ionization energy than the carrier gas.

7. The system of claim 4, wherein the scavenger gas comprises methane and ammonia.

8. The system of claim 6, wherein the concentration of ammonia is between about 1% and about 10%.

9. The system of claim 1, wherein the carrier gas is nitrogen.

10. The system of claim 1, wherein the carrier gas is hydrogen.

11. A method for reducing peak tailing and reaction when a carrier gas other than helium is used for gas chromatography-mass spectrometry (GC-MS), the method comprising: separating the compounds using a gas chromatography column that uses a carrier gas other than helium; providing the column output to an ionization chamber of a mass spectrometer; providing a scavenger gas to an ionization chamber of the mass spectrometer; ionizing the compound in the presence of the carrier gas and the scavenger gas; as well as The ionized compounds are analyzed using the mass spectrometer.

12. The method of claim 11, wherein the scavenger gas has a lower ionization energy than the carrier gas.

13. The method of claim 11, wherein the scavenger gas is methane.

14. The method of claim 11, wherein the scavenger gas is isobutane.

15. The method of claim 11, wherein the scavenger gas comprises two or more gas species.

16. The method of claim 15, wherein each of the carrier gas species has a lower ionization energy than the carrier gas.

17. The method of claim 15, wherein the scavenger gas comprises methane and ammonia.

18. The method of claim 17, wherein the concentration of ammonia is between about 1% and about 10%.

19. The method of claim 11, wherein the carrier gas is nitrogen.

20. The method of claim 11, wherein the carrier gas is hydrogen.

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