JP2006189298A - Gas chromatograph mass spectrometer and reduction method of background using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas chromatograph mass spectrometer capable of removing fundamentally He<SP>*</SP>which is a main cause of a background originated in He. <P>SOLUTION: An electron source 38 for He<SP>*</SP>ionization is provided between an ionization chamber 32 and QMF 36 disposed in a vacuum chamber 31 of an MS part 30, and He<SP>*</SP>emitted from the ionization chamber 32 is irradiated with electrons having proper energy, and thereby ionized into He<SP>+</SP>. Otherwise, a collision chamber is provided between the ionization chamber 32 and the QMF 36, and the collision chamber is filled with N<SB>2</SB>gas by a gas supply part, and He<SP>*</SP>emitted from the ionization chamber 32 is interacted with N<SB>2</SB>in the collision chamber, and thereby changed into He in the ground state. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a gas chromatograph mass spectrometer.

  As shown in FIG. 5, a gas chromatograph mass spectrometer (hereinafter abbreviated as GCMS) includes a gas chromatograph part (hereinafter abbreviated as GC part) 10 for temporally separating components mixed in a sample, The interface unit 20 has a configuration in which a mass analysis unit (hereinafter abbreviated as MS unit) 30 for separating and detecting components separated by the GC unit 10 based on the mass number (mass / charge) is connected. ing. The MS unit 30 includes an ionization chamber 32 in which an ionization electron source 33 for ionizing a sample is disposed, a QMF (Quadrupole-mass-filter) that separates the ionized sample based on mass, and the like. Mass separator 36 and a detector 37 for detecting ions separated by the mass separator 36. Ions generated in the ionization chamber 32 are extracted from the ionization chamber 32 due to a potential difference between the ionization chamber 32 and the extraction electrode 34 and enter the mass separator 36 through the ion transport optical system 35.

The sample is mixed with a rare gas (usually using He) as a carrier gas, introduced into the GC unit 10, separated by the column 12 of the GC unit 10, and introduced into the ionization chamber 32 of the MS unit 30. Normally, the sample is ionized in the ionization chamber 32 by a 70 eV electron beam. At this time, the He gas flowing into the ionization chamber 32 together with the sample is also ionized and excited. When He is ionized, He ⁺ (ionization energy: 24.6 eV) is generated, but when He is excited to a metastable state with a higher energy level than the ground state and a long lifetime, He ^* (metastable helium , 2 ¹ S He ^* excitation energy: 20.61 eV, 2 ³ S He ^* excitation energy: 19.82 eV).

He ⁺ or He ^* generated from the carrier gas He becomes a background component that cannot be ignored when performing high-sensitivity analysis, and causes a decrease in the S / N ratio. However, of He from the background, due to He ^+, by providing a suitable electromagnetic field, He ⁺ it is possible to remove before reaching the ion detector 37.

On the other hand, since He ^* is electrically neutral, it cannot be removed by an electromagnetic field. He ^* remaining in the vacuum chamber 31 behaves as a carrier for carrying energy and interacts with surrounding atoms / molecules to cause an ionization phenomenon. For example, when a metal surface atom and He ^* interact, He ^* gives an electron to the metal surface atom and becomes He ⁺ . Such a phenomenon is called resonance ionization. Further, when an insulator such as residual gas (X) in the apparatus interacts with He ^* , the partner atom (molecule) is ionized to generate X ⁺ . Such a phenomenon is called Penning ionization. That is, the background due to the He ^*, not only caused by the He ^* itself reaches the detector 37, with He ⁺ or X ⁺ is a detector 37 that is generated from the He ^* secondarily Some are caused by being detected.

Note that metastable states also exist in rare gases other than He, and the same problem arises when these are used as a carrier gas for GCMS. However, among metastable rare gases, the internal energy of He ^* is the largest, and ionization is likely to occur due to interactions with other atoms and molecules.

In order to reduce such background, an off-axis GCMS in which the optical axes of the optical elements constituting the apparatus are partially offset from the same straight line has been developed ( Patent Document 1). This is because the optical axis is shifted between the ionization chamber and the mass separator or between the mass separator and the detector, and the straight traveling He ^* is deviated from the ion optical axis to the mass separator or detector. By preventing entry, the background caused by He ^* is suppressed.

U.S. Pat.No. 3,410,997

  In the off-axis GCMS as described above, in order to connect optical elements whose optical axes are not arranged on the same straight line, as shown in FIG. 6, ions having a curved optical axis between them are used. It is necessary to provide the transport optical system 60. Such an ion transport optical system 60 has a problem that the manufacturing cost of the apparatus is increased because the degree of difficulty in design and manufacture is higher than that of a general ion transport optical system having a linear optical axis. . Further, in the ion transport optical system 60 having such a curved optical axis, signal ions may be lost.

Further, according to the off-axis method, although it is possible to remove the He ^* coming proceeds to QMF with directivity, He ^* and which flows while floating, and the straight line collides with He or residual gas He ^* taking different trajectories may fly along the ion transport optical system 60 having the curved optical axis and cannot be removed. Further, He ^* deviating from the ion transport optical system 60 collides with the inner wall of the vacuum chamber to become He ⁺ , or interacts with the residual gas X to generate X ⁺ , so that these secondary ions are generated. May reach the ion detector.

Therefore, the problem to be solved by the present invention is to provide a gas chromatograph mass spectrometer capable of fundamentally removing He ^* , which is the main cause of the He-derived background, with a simple structure.

In order to solve the above problems, the first aspect of the gas chromatograph mass spectrometer according to the present invention is introduced from a gas chromatograph unit having a column for temporally separating a sample and a gas chromatograph unit. In a gas chromatograph mass spectrometer equipped with an ionization chamber for ionizing a sample, a mass separator for separating the ions based on mass, and a mass analyzer equipped with an ion detector for detecting mass-separated ions,
An electron irradiation means or a photon irradiation means for ionizing a metastable noble gas generated in the ionization chamber is provided between the ionization chamber and the mass separator.

  When the purpose is to reduce the background without fragmenting the signal ions coming out of the ionization chamber, the electron (or photon) energy irradiated by the electron irradiation means (or photon irradiation means) is used. Is set to the minimum energy required to ionize the metastable noble gas derived from the carrier gas. In addition, when it is desired to actively fragment signal ions emitted from the ionization chamber by electron (photon) irradiation, ionization of metastable rare gas generated in the ionization chamber and fragmentation of signal ions are possible. In addition, the energy is set so as not to newly generate a metastable rare gas.

A gas chromatograph mass spectrometer according to a second aspect of the present invention includes a gas chromatograph unit having a column for temporally separating a sample, an ionization chamber for ionizing a sample introduced from the gas chromatograph unit, In a gas chromatograph mass spectrometer equipped with a mass separator that separates the ions based on mass, and a mass analyzer equipped with an ion detector that detects the mass-separated ions,
Gas supply means for introducing neutral gas molecules is provided in the space between the ionization chamber and the mass separator and / or in the space inside the mass separator.

  In the gas chromatograph mass spectrometer of the second aspect, a collision chamber is provided between the ionization chamber and the mass separator, and neutral gas molecules are introduced into the collision chamber by the gas supply means. Also good.

Note that N ₂ or He is preferably used as the neutral gas molecule.

In the first aspect of the gas chromatograph mass spectrometer of the present invention described above, removal by a mass separator is performed by applying appropriate energy to He ^* by irradiating electrons or photons to ionize He ^* , and making it He ^+. The background can be reduced by preventing He ^* and secondary ions derived therefrom from being detected by the detector. In addition, by appropriately setting the energy of electrons or photons irradiated to He ^* at this time, it is possible to prevent fragmentation of signal ions or to actively generate signal ions. it can.

In the second aspect of the gas chromatograph mass spectrometer of the present invention, a neutral gas is previously introduced into the space between the ionization chamber and the mass separator and / or the space inside the mass separator by the gas supply means. By introducing molecules, the background caused by He ^* can be suppressed. This is probably because He ^* coming out of the ionization chamber interacts with N ₂ molecules, etc., and ionizes the partner molecule, and at the same time changes itself to He (Penning ionization), or He ^* coming out of the ionization chamber By colliding with He molecules introduced into the device by the gas supply means, the amount of He ^* flowing downstream of the QMF decreases due to loss of internal energy and relaxation to the ground state He. Conceivable. In addition, such a gas also has an effect of converging the signal ion on the optical axis by colliding with the signal ion, and thereby, the intensity of the signal ion can be increased simultaneously with the reduction of the background, Analysis with a higher S / N ratio can be realized.

In any of the above-described chromatographic mass spectrometers, He ^* can be fundamentally removed without using an off-axis method, so that the manufacturing cost can be reduced and the curved optical axis optical system can be suppressed. There is no loss of signal ions, which is a concern when using, and the background can be reduced while maintaining the signal intensity.

  Hereinafter, the best mode for carrying out the present invention will be described using embodiments.

[Example 1]
As shown in FIG. 1, the gas chromatograph mass spectrometer of the present embodiment has a configuration in which a GC unit 10 and an MS unit 30 are connected by an interface unit 20.

  In the GC unit 10, a carrier gas (He gas) having a predetermined flow rate is supplied to a column (capillary column) 12 heated to an appropriate temperature by a column oven 13 through a sample vaporization chamber that is a part of the injector 11. The liquid sample supplied and injected into the sample vaporizing chamber by a microsyringe or the like is immediately vaporized and is carried in the carrier gas flow and sent into the column 12. While passing through the column 12, each component in the sample gas is temporally separated and reaches its outlet, and is introduced into the ionization chamber 32 of the MS unit 30 from the sample introduction tube 21 through the interface unit 20.

  In the MS unit 30, an ionization electron source 33 for generating an electron beam is attached to the ionization chamber 32, and sample molecules introduced into the ionization chamber 32 are ionized by the electron beam. The generated ions are extracted to the outside of the ionization chamber 32 by the electric field generated by the extraction electrode 34, converged by the ion transport optical system 35 having a linear optical axis, and in the long axis direction of the QMF (or other mass separator) 36. Introduced into space. A voltage obtained by superimposing a DC voltage and a high-frequency voltage is applied to the QMF 36, and only ions having a mass number (mass m / charge z) corresponding to the applied voltage pass through the space in the major axis direction, and the detector 37 Will be detected. The ionization chamber 32, the ion transport optical system 35, the QMF 36, and the detector 37 are disposed in a vacuum chamber 31 that is vacuumed by a vacuum pump (not shown).

In the ion transport optical system 35 region, as shown in FIG. 2, a He ^* ionization electron source 38 for ionizing He ^* emitted from the ionization chamber 32 is provided. The electron beam generated from the electron source 38 is irradiated on the optical path between the ionization chamber 32 / QMF 36 through the electrodes constituting the ion transport optical system 35, and the He beam exiting the ionization chamber 32 by the electron beam. ^* Is excited and converted to He ⁺ . It should be noted that the He ⁺ generated in the ion transport optical system 35 region in this way can be removed separately from the signal ions by the mass separation function of the subsequent QMF 36.

In the gas chromatograph mass spectrometer of the present embodiment, when it is desired to remove He ^* without fragmenting signal ions, the He ^* ionization electron source 38 is set to the minimum necessary for ionization of He ^* . Setting is made so that electrons having energy are irradiated, and conversely, when it is desired to actively fragment signal ions, setting is made so that electrons having relatively large energy are irradiated. However, at this time, in order to avoid generation of new He ^* , the energy of the irradiated electrons is made lower than the excitation energy of He ^* . Here, the energy required to ionize the ground state He to He ⁺ is 24.6 eV, and the energy required to excite the ground state He to the metastable He ^* is 2 ¹ S He ^* . In 20.61 eV, 2 ³ S He ^* , it is 19.82 eV. Therefore, specifically, by irradiating He ^* with electrons or photons having energy of 4.78 eV or more, it is possible to ionize He ^* to He ⁺ , and when fragmentation of signal ions is to be suppressed. , When irradiating electrons (photons) with energy not significantly greater than 4.78 eV and intentionally causing fragmentation of signal ions, irradiate electrons (photons) with higher energy below 19.82 eV .

Thus, the gas chromatograph mass spectrometer of this example does not deviate He ^* from the optical path as in the off-axis method, but fundamentally removes He ^* by ionizing by irradiation with an electron beam. There is no generation of secondary background ions, and the background can be reduced efficiently.

The gas chromatograph mass spectrometer of the above embodiment may further include a plurality of He ^* ionization electron (or photon) sources as described above. With such a configuration, the He ^* ionization region can be increased and the amount of He ^* removal can be easily increased.

[Example 2]
The configuration of the gas chromatograph mass spectrometer of this example is shown in FIGS. In addition, the same code | symbol is attached | subjected about the structure similar to the said Example 1, and description is abbreviate | omitted.

In the gas chromatograph mass spectrometer of this embodiment, a collision chamber 39 for holding gas molecules is provided between the ionization chamber 32 and the QMF 36, and N ₂ is provided in the space inside the collision chamber 39 by a gas supply unit 40. Gas molecules are introduced. The collision chamber 39 also serves as the ion transport optical system 35, and has a plurality of electrodes therein, and an appropriate RF voltage / DC voltage is applied to these electrodes for transport of signal ions.

He ^* flowing in from the ionization chamber 32 interacts with N ₂ in the collision chamber 39 to ionize N ₂ and itself becomes ground state He (Penning ionization). As a result, the amount of He ^* flowing into the QMF 36 can be reduced, and generation of secondary background ions due to He ^* can be suppressed. Note that N ₂ ⁺ generated by Penning ionization flows into the QMF 36 together with the signal ions, where they are distinguished from the signal ions by the mass separation function of the QMF 36 and removed. As a result, it is possible to improve the S / N ratio in high sensitivity analysis in which the He-derived background becomes a problem.

Further, when the signal ions generated in the ionization chamber 32 are transported to the QMF 36 by the electric field generated by the electrode of the ion transport optical system 35, the signal ions collide with the N ₂ in the collision chamber 39 at an appropriate frequency. Are collected on the optical axis, and the rate of introduction of ions into the QMF 36 is increased. Therefore, by optimizing the gas type and pressure in the collision chamber 39, He ^* can be relaxed to He, and at the same time, the signal ion intensity can be increased, and an analysis with a higher S / N ratio can be realized. it can.

In addition, the background derived from He ^* can be reduced by introducing He gas molecules directly into the vacuum chamber without providing a collision chamber as described above. In this case, He ^* exiting from the ionization chamber collides with the He gas molecules while passing through the ion transport optical system region or the QMF region, loses internal energy, and is relaxed to He. ^* It is thought that the background derived from is reduced.

  As described above, the best mode for carrying out the gas chromatograph mass spectrometer of the present invention has been described using examples, but the present invention is not limited to this, and various modifications can be made within the scope of the present invention. Is acceptable. For example, the gas chromatograph mass spectrometer of the present invention is not limited to the case where He is used as a carrier gas as described above, but can be similarly applied to the case where other rare gas is used as a carrier gas.

BRIEF DESCRIPTION OF THE DRAWINGS Sectional drawing which shows schematic structure of the gas chromatograph mass spectrometer which is a 1st Example of this invention. Sectional drawing which shows the structure of the ionization chamber and ion transport optical system periphery of the gas chromatograph mass spectrometer of the Example. Sectional drawing which shows schematic structure of the gas chromatograph mass spectrometer which is the 2nd Example of this invention. Sectional drawing which shows the structure of the ionization chamber and ion transport optical system periphery of the gas chromatograph mass spectrometer of the Example. Sectional drawing which shows schematic structure of the conventional gas chromatograph mass spectrometer. The figure which shows the ion transport optical system which has a curvilinear optical axis.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... GC part 11 ... Injector 12 ... Column 13 ... Column oven 20 ... Interface part 21 ... Sample introduction tube 30 ... MS part 31 ... Vacuum chamber 32 ... Ionization chamber 33 ... Electron source 34 for ionization ... Extraction electrodes 35, 60 ... Ion Transport optics 36 ... Mass separator (QMF)
37 ... Ion detector 38 ... He ^* Electron source for ionization 39 ... Collision chamber 40 ... Gas supply section

Claims (6)

A gas chromatograph unit having a column for temporally separating a sample, an ionization chamber for ionizing a sample introduced from the gas chromatograph unit, a mass separator for separating the ions based on mass, and a mass separated ion In a gas chromatograph mass spectrometer equipped with a mass spectrometer equipped with an ion detector for detection,
A gas chromatograph mass spectrometer comprising an electron irradiation means or a photon irradiation means for ionizing a metastable noble gas generated in the ionization chamber between the ionization chamber and a mass separator.   The electron or photon having a minimum energy necessary for ionizing the metastable rare gas generated in the ionization chamber is irradiated by the electron irradiation unit or the photon irradiation unit. A method for reducing background in a gas chromatograph mass spectrometer.   By the electron irradiation means or the photon irradiation means, ionization of metastable rare gas generated in the ionization chamber and fragmentation of signal ions are possible, and no metastable noble gas is newly generated. 2. The method for reducing background in a gas chromatograph mass spectrometer according to claim 1, wherein electrons or photons having energy are irradiated. A gas chromatograph unit having a column for temporally separating a sample, an ionization chamber for ionizing a sample introduced from the gas chromatograph unit, a mass separator for separating the ions based on mass, and mass separation In a gas chromatograph mass spectrometer equipped with a mass spectrometer equipped with an ion detector for detecting ions,
A gas chromatograph mass spectrometer comprising gas supply means for introducing neutral gas molecules into a space between the ionization chamber and a mass separator and / or a space inside the mass separator.   5. The gas chromatograph mass spectrometer according to claim 4, further comprising a collision chamber between the ionization chamber and the mass separator, wherein the gas supply means introduces neutral gas molecules into the collision chamber. . The gas chromatograph mass spectrometer according to claim 4 or 5, wherein the neutral gas molecule is N ₂ or He.

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