Gas chromatography-mass spectrometry method and gas chromatography-mass spectrometer

Abstract

The present invention provides a gas chromatograph-mass spectrometry method and a gas chromatograph-mass spectrometer that can enhance analytical sensitivity without limitations on the type of analyte. [Solution] The gas chromatography-mass spectrometry method includes the steps of: supplying a nitrogen carrier gas containing the analyte from one end of the column 11 in the longitudinal direction of the gas chromatograph 1; ionizing the analyte in the chamber 25 while the analyte flowing out from the other end of the column 11 and a hydrocarbon gas containing hydrocarbons are supplied to the chamber 25; and analyzing the mass of the ionized analyte. The flow rate of the hydrocarbon gas supplied into the chamber 25 is set to 1 / 10 or less of the flow rate of the nitrogen carrier gas containing the analyte supplied into the chamber 25.

Description

Technical Field

[0001] The present invention relates to a gas chromatography mass spectrometry method under nitrogen carrier conditions substituting for helium and a high-sensitivity technique by adding an ultra-trace matrix gas to the ion source of a gas chromatography mass spectrometer.

Background Art

[0002] An analyzer comprising a gas chromatograph using hydrogen as a helium-substituting carrier gas and equipped with an electron ionization mass spectrometer as a detector has been proposed (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the analyzer described in Patent Document 1, since hydrogen is used as the carrier gas, substances that are likely to cause a hydrogen addition reaction cannot be adopted as detection targets, and accordingly, the types of analysis target substances are limited. On the other hand, it is conceivable to adopt nitrogen gas, which is an inert gas, as the carrier gas instead of hydrogen. However, in this case, a large amount of nitrogen ions are generated in the electron ionization detector, which may lead to a decrease in analysis sensitivity due to a low ionization efficiency of the analysis target substance in the ion source. Also, although analysis is performed using a gas chromatography mass spectrometer with nitrogen as the carrier gas, there are problems such as a significant reduction in sensitivity.

[0005] This invention has been made in view of the above reasons, and aims to provide a gas chromatograph-mass spectrometry method and a gas chromatograph-mass spectrometer that can increase analytical sensitivity without being limited by the type of analyte. Furthermore, it aims to provide a gas chromatograph-mass spectrometry method and a gas chromatograph-mass spectrometer in which fragmentation of the analyte occurs in the same manner as electron ionization under helium carrier conditions. [Means for solving the problem]

[0006] The gas chromatography-mass spectrometry method according to the present invention is A gas chromatograph having a long tubular column, comprising the step of supplying a nitrogen carrier gas containing the analyte from one end in the longitudinal direction of the column, The process involves supplying the analyte flowing out from the other end of the column and an organic gas containing organic matter or an inorganic gas containing inorganic matter with an ionization energy of 14.5 eV or less into the chamber, and ionizing the analyte within the chamber. The step includes analyzing the mass of the ionized analyte, The amount of organic matter contained in the organic gas or inorganic matter contained in the inorganic gas supplied into the chamber per unit time is set to be 1 / 10 or less of the amount of nitrogen carrier gas containing the analyte supplied into the chamber per unit time.

[0007] From another perspective, the gas chromatograph-mass spectrometer according to the present invention is: A gas chromatograph having a long tubular column and a gas supply unit that supplies a nitrogen carrier gas containing the analyte from one end of the column in the longitudinal direction, The column has a chamber into which the analyte flowing out from the other end is supplied, and an ion source is provided within the chamber to ionize the analyte. A mass spectrometer unit for analyzing the mass of the ionized substance to be analyzed released from the ion source, The chamber comprises a matrix gas supply unit that supplies an organic gas containing organic matter or an inorganic gas containing inorganic matter with an ionization energy of 14.5 eV or less into the chamber. The amount of organic matter contained in the organic gas supplied to the chamber per unit time is set to be 1 / 10 or less of the amount of nitrogen carrier gas containing the analyte supplied to the chamber per unit time. [Effects of the Invention]

[0008] In the gas chromatograph mass spectrometry method and gas chromatograph mass spectrometer according to the present invention, a nitrogen carrier gas containing the analyte is supplied from one end of a column, and the analyte flowing out from the other end of the column, along with an organic gas containing organic matter or an inorganic gas containing inorganic matter with an ionization energy of 14.5 eV or less, is supplied into the chamber. The analyte is then ionized in the chamber, and the mass of the ionized analyte is analyzed. The amount of organic matter contained in the organic gas, such as hydrocarbon gas, supplied into the chamber per unit time is set to 1 / 10 or less of the amount of nitrogen carrier gas containing the analyte supplied into the chamber per unit time. This improves the ionization efficiency of the analyte in the chamber due to the matrix effect of ionized nitrogen by hydrocarbons, thereby increasing the analytical sensitivity in the mass spectrometer without limiting the type of analyte. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram of a gas chromatograph-mass spectrometer according to an embodiment of the present invention. [Figure 2] This is a schematic diagram showing a part of the gas chromatograph-mass spectrometer according to an embodiment. [Figure 3] This figure shows an example of a chromatogram according to an embodiment. [Figure 4](A) is a figure showing the mass spectral measurement results and mass spectral library for diethyl phthalate, (B) is a figure showing the mass spectral measurement results and mass spectral library for dibutyl phthalate, (C) is a figure showing the mass spectral measurement results and mass spectral library for bis(2-ethylhexyl) phthalate, and (D) is a figure showing the mass spectral measurement results and mass spectral library for di-n-octyl phthalate. [Modes for carrying out the invention]

[0010] The gas chromatograph mass spectrometry method according to the embodiment of the present invention includes the steps of: supplying a nitrogen carrier gas containing the analyte from one end in the longitudinal direction of the column of a gas chromatograph having a long tubular column; ionizing the analyte in a chamber while the analyte flowing out from the other end of the column and an organic gas containing organic matter or an inorganic gas containing inorganic matter with an ionization energy of 14.5 eV or less are supplied into the chamber; and analyzing the mass of the ionized analyte. The amount of organic matter such as hydrocarbons contained in the organic gas supplied into the chamber per unit time is set to 1 / 10 or less of the amount of nitrogen carrier gas containing the analyte supplied into the chamber per unit time. Here, the analyte is, for example, a polycyclic aromatic hydrocarbon (hereinafter referred to as "PAHs") with a molecular weight of 50 or more.

[0011] In the gas chromatography-mass spectrometry method according to this embodiment, a gas chromatography-mass spectrometry (hereinafter referred to as "GCMS") apparatus, such as the one shown in Figure 1, is used. This GCMS apparatus comprises a gas chromatograph 1, a mass spectrometry unit 2, a carrier gas supply unit 6, an analyte supply unit 3, a matrix gas supply unit 5, and a matrix gas supply control unit 4. The carrier gas supply unit 6 supplies nitrogen carrier gas into the supply pipe L2. Here, as the nitrogen carrier gas, if the molecular weight of the analyte is 50 or more, a gas containing at least molecules with a molecular weight of less than 50 is used, for example, a so-called G1 class nitrogen gas with a purity of 99.99995 vol.% is used. The carrier gas supply unit 6 controls the flow rate of nitrogen carrier gas supplied to the supply pipe L2 so that the flow rate of nitrogen carrier gas supplied from the column 11 (described later) to the chamber 211 of the ion source 21 (described later) is constant within the range of 0.5 ml / min or more and 1.2 ml / min.

[0012] The analyte supply unit 3 supplies the analyte to the supply pipe L2.

[0013] The gas chromatograph 1 includes a long, tubular column 11 and a gas introduction unit 12 connected to one end of the column 11 in the longitudinal direction for introducing a nitrogen carrier gas containing the analyte into the column 11. The gas introduction unit 12 is connected to a supply pipe L2. The other end of the column 11 is held at the interface 27 of the mass spectrometry unit 2. For example, the stationary phase of the column 11 may include diphenyl and dimethylpolysiloxane. The gas chromatograph 1 also has a temperature control unit (not shown) for maintaining a constant temperature of the column 11, for example, at 320°C.

[0014] The mass spectrometry unit 2 includes an ion source 21, a lens 22, a mass spectrometry unit 23, a detector 24, a chamber 25, a vacuum pump 26, and an interface 27. As shown in Figure 2, the ion source 21 includes a chamber 211, an electrode 212, a filament 213, a current source 214 that supplies current to the filament 213, and a constant voltage source 215 that maintains the potential of the filament 213 at a lower potential than the potential of the electrode 212. The ion source 21 also has a heating unit (not shown) that heats the chamber 211. The chamber 211 has a release hole 211a in a part of the peripheral wall of the chamber 211 for releasing fragment ions of the analyte generated in the chamber 211 to the outside of the chamber 211. The electrode 212 is maintained at ground potential. The ion source 21 ionizes the analyte, nitrogen, and hydrocarbons by an electron ionization method, which involves ionizing them by colliding them with thermionic electrons emitted from the filament 213. Specifically, thermionic electrons emitted from the filament 213 collide with the analyte and nitrogen supplied from the column 11 into the chamber 211, and with hydrocarbons supplied from the capillary 43 (described later) of the matrix gas supply control unit 4.

[0015] Lens 22 is an electron lens that focuses fragment ions of the analyte emitted from the emission port 211a of the chamber 211 of the ion source 21 to the mass spectrometry unit 23. The mass spectrometry unit 23 is, for example, a quadrupole mass spectrometer, which separates only the fragment ions of the analyte and transmits them to the detector 24 by changing the voltage applied to four electrodes arranged around the region through which the ionized analyte passes. The detector 24 has, for example, a secondary electron multiplier tube and detects the fragment ions that reach the detector 24.

[0016] The chamber 25 has an ion source 21, a lens 22, a mass spectrometry section 23, and a detector 24 disposed inside, and the inside is maintained at a high vacuum by a vacuum pump 26. As the vacuum pump 26, for example, one including a turbomolecular pump is adopted. The interface 27 is tubular, and a part of the column 11 and a part of the capillary 43 of the matrix gas supply control unit 4 are inserted inside, and has a structure for guiding the column 11 and the capillary 43 to the ion source 21.

[0017] The matrix gas supply unit 5 supplies an organic gas containing an organic substance to the matrix gas supply control unit 4 through the supply pipe L1. As the organic gas, for example, a hydrocarbon gas containing ethane with a concentration of 4% can be adopted.

[0018] The matrix gas supply control unit 4 has a pressure adjustment unit 41, a pressure control unit 42 for controlling the pressure adjustment unit 41, and a capillary 43 that is long and tubular and has one end in the longitudinal direction connected to the pressure adjustment unit 41. As the capillary 43, for example, one with an inner diameter of 0.1 mm or more and 0.05 mm or less can be adopted. The pressure adjustment unit 41 has a pressure adjustment valve (not shown) that is connected to the matrix gas supply unit 5 on the primary side through the supply pipe L1, is connected to the capillary 43 on the secondary side, and reduces the pressure of the matrix gas supplied from the primary side and discharges it to the secondary side. The pressure control unit 42 controls the pressure adjustment valve so that the secondary side pressure of the pressure adjustment valve of the pressure adjustment unit 41 is a constant pressure within the range of 100 kPa or more and 500 kPa or less, and the flow rate of the matrix gas supplied into the chamber 211 of the ion source 21 is 0.05 ml / min or more and 0.2 ml / min or less, and is 1 / 6 or less of the flow rate of the nitrogen carrier gas containing the analyte supplied into the chamber 211.

[0019] Here, the results of measuring the chromatogram using the gas chromatograph mass spectrometer according to the present embodiment will be described while comparing with the results of measuring the chromatogram using the gas chromatograph mass spectrometer according to the comparative example. The gas chromatograph mass spectrometer according to the comparative example is configured to employ a nitrogen carrier gas and not supply a hydrocarbon gas into the chamber 211 of the ion source 21. As shown in FIG. 3, in the present embodiment, it was found that for any of diethyl phthalate, dibutyl phthalate, bis(2-ethylhexyl) phthalate, and di-n-octyl phthalate, intensity peaks larger than those in the comparative example were obtained. This suggests that even when nitrogen is used as the carrier gas, the sensitivity can be enhanced compared to the comparative example.

[0020] Further, the results of confirming the degree of coincidence between the mass spectra obtained for diethyl phthalate, dibutyl phthalate, bis(2-ethylhexyl) phthalate, and di-n-octyl phthalate respectively using the gas chromatograph mass spectrometer according to the present embodiment and the mass spectra registered in the mass spectral library are shown in FIGS. 4(A) to (D). As shown in FIGS. 4(A) to (D), it can be seen that for any substance, a high degree of coincidence of 93% or more is shown. From this, it can be understood that in the present embodiment, qualitative analysis of the analyte substance utilizing the mass spectral library can be performed with relatively high accuracy.

[0021] As described above, in the gas chromatograph mass spectrometry method and gas chromatograph mass spectrometer according to this embodiment, a nitrogen carrier gas containing the analyte is supplied from one end of the column 11, and the nitrogen carrier gas flowing out from the other end of the column 11 and a hydrocarbon gas containing hydrocarbons are supplied into the chamber 211 of the ion source 21. The analyte is then ionized in the chamber 211, and the mass of the ionized analyte is analyzed. The amount of hydrocarbons supplied to the chamber 211 per unit time is set to 1 / 10 or less of the amount of nitrogen carrier gas containing the analyte supplied to the chamber 211 per unit time. As a result, the ionization efficiency of the analyte can be increased in the chamber 211 due to the matrix effect of ionized nitrogen by hydrocarbons, thereby increasing the analytical sensitivity in the mass spectrometer 23 without any limitations on the type of analyte.

[0022] Incidentally, in order to perform gas chromatography-mass spectrometry with high sensitivity, it is most preferable to use He gas as the carrier gas. However, He gas is currently a rare gas, difficult to obtain, and relatively expensive. Therefore, hydrogen gas is sometimes used as a carrier gas to replace He gas. However, hydrogen gas is highly flammable, and in some cases, the analyte must be limited to substances that do not undergo hydrogenation reactions easily. In contrast, the use of nitrogen gas, which has low flammability and reactivity, as a carrier gas has been considered, but with conventional methods, the analytical sensitivity has decreased to about 1 / 20, and high analytical sensitivity could not be obtained. In contrast, in this embodiment, by supplying a small amount of matrix gas, compared to the nitrogen carrier gas, into the chamber 211 of the ion source 21 along with the nitrogen carrier gas, the decrease in analytical sensitivity is suppressed, and analytical sensitivity equivalent to that when He gas is used as the carrier gas is achieved. As a result, qualitative analysis at the same level as when He gas is used as the carrier gas by utilizing a mass spectrum library is possible.

[0023] Another ionization technique used in the field of mass spectrometry is chemical ionization (CI). This chemical ionization technique involves protonating the analyte by, for example, including methane, ammonia, etc., along with the analyte in a helium gas carrier. In mass spectrometry, the analytical sensitivity is increased by detecting molecular ions in which the mass of the analyte molecule has increased by one due to protonation. In contrast, the gas chromatography-mass spectrometry method according to this embodiment increases analytical sensitivity by suppressing the protonation of the analyte while causing energy transfer and charge transfer to the analyte by including a matrix gas in the nitrogen carrier gas. This method is based on a different mechanism from the aforementioned chemical ionization technique.

[0024] Although embodiments of the present invention have been described above, the present invention is not limited to the configuration of the embodiments described above. It is not fixed. For example, a hydrocarbon gas containing hydrocarbons other than ethane may be used as the matrix gas. Examples of other hydrocarbons include ethylene, acetylene, and methane. Furthermore, the matrix gas may be an inorganic gas containing inorganic substances with an ionization energy of 14.5 eV or less, not just organic gases. Examples of inorganic gases include hydrogen gas and argon gas. When hydrogen gas is used as the matrix gas, there is an advantage in that the range of mass number and molecular weight of the analyte can be made smaller. [Industrial applicability]

[0025] This invention is suitable for gas chromatography-mass spectrometry in the fields of pharmaceutical development, environmental analysis, and other fields requiring trace analysis techniques. [Explanation of symbols]

[0026] 1: Gas chromatograph, 2: Mass spectrometry unit, 3: Analyte supply unit, 4: Matrix gas supply control unit, 5: Matrix gas supply unit, 6: Carrier gas supply unit, 11: Column, 12: Gas introduction unit, 21: Ion source, 22: Lens, 23: Mass spectrometry unit, 24: Detector, 25: Chamber, 26: Vacuum pump, 27: Interface, 41: Pressure adjustment unit, 42: Pressure control unit, 43: Capillary, 211: Chamber, 211a: Discharge port, 212: Electrode, 213: Filament, 214: Current source, 215: Constant voltage source, L1, L2: Feed tubes

Claims

1. A gas chromatograph having a long tubular column, comprising the step of supplying a nitrogen carrier gas containing the analyte from one end of the column in the longitudinal direction, The process involves supplying the analyte flowing out from the other end of the column and an organic gas containing organic matter or an inorganic gas containing inorganic matter with an ionization energy of 14.5 eV or less into the chamber, and ionizing the analyte within the chamber. The step includes analyzing the mass of the ionized analyte, The amount of organic matter contained in the organic gas or inorganic matter contained in the inorganic gas supplied into the chamber per unit time is set to be 1 / 10 or less of the amount of nitrogen carrier gas containing the analyte supplied into the chamber per unit time. Gas chromatography-mass spectrometry method.

2. The flow rate of the aforementioned organic gas is 0.05 ml / min or more and 0.2 ml / min or less. The flow rate of the nitrogen carrier gas containing the substance to be analyzed is 0.5 ml / min or more and 1.2 ml / min or less. The gas chromatograph mass spectrometry method according to claim 1.

3. The aforementioned organic substance is ethane, The concentration of ethane in the aforementioned organic gas is 2% or more and 5% or less. The gas chromatograph mass spectrometry method according to claim 2.

4. A gas chromatograph having a long tubular column and a gas supply unit that supplies a nitrogen carrier gas containing the analyte from one end of the column in the longitudinal direction, The column has a chamber into which the analyte flowing out from the other end is supplied, and an ion source is provided within the chamber to ionize the analyte. A mass spectrometer unit for analyzing the mass of the ionized substance to be analyzed released from the ion source, The chamber is provided with a matrix gas supply unit that supplies an organic gas containing organic matter or an inorganic gas containing inorganic matter with an ionization energy of 14.5 eV or less. The amount of organic matter contained in the organic gas or inorganic matter contained in the inorganic gas supplied into the chamber per unit time is set to be 1 / 10 or less of the amount of nitrogen carrier gas containing the analyte supplied into the chamber per unit time. Gas chromatograph-mass spectrometer.

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