JP2009129868A - Mass spectroscope and its method for adjustment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance a signal intensity relevant to a molecular weight with less cleavage when ionizing a molecular specimen, even when an EI/CI convertible ionization chamber is used with less sealing density than that of the CI-exclusive ionization chamber. <P>SOLUTION: To a reagent ion gas m/z 41 is paid attention among various kinds of the reagent gases when methane is used for the reagent gas of a CI, a repeller voltage is checked to maximize the signal intensity of the ion (S5), and a parameter such as a lens voltage is determined so as to maximize the signal intensity of the m/z designated by an analyzer in charge under the fixed condition of the repeller voltage to a checked value (S6). Because the ion of the m/z 41 is highly dependent on the repeller voltage of the signal intensity, the suitable repeller voltage can be easily and certainly found out. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a mass spectrometer and an adjustment method thereof, and more particularly, to a mass spectrometer including an ion source that ionizes a gaseous sample by chemical ionization (CI) and an adjustment method thereof.

  When ionizing a gaseous sample such as a gas chromatograph mass spectrometer (GC / MS) that combines a gas chromatograph and a mass spectrometer, an electron ionization method (EI, also called an electron impact ionization method) or a chemical ionization method ( CI) is generally used.

  In EI, thermal electrons generated by a filament are accelerated and brought into contact with gaseous sample molecules. Then, electrons are emitted from the sample molecules, and the sample molecules are ionized. In general, since ions generated by EI have excessive internal energy, fragment ions are easily generated due to cleavage. For this reason, it is a particularly useful ionization method for the purpose of obtaining the structure of the original molecule by examining the cleavage state.

On the other hand, in CI, a reagent gas such as methane or isobutane is introduced into an ionization chamber, and thermal electrons are brought into contact with the reagent gas molecules to produce a large amount of reagent gas ions (for example, CH ₅ ⁺ , (CH ₃ ) ₃ C ^+, etc.). To generate. Then, sample molecules are ionized by introducing sample molecules into the reagent gas ion atmosphere and causing a chemical reaction. For example, when methane (CH ₄ ) is used as the reagent gas, ions having a mass of M + 1 are mainly generated with respect to sample molecules having a molecular weight of M. In this method, since ionization is performed relatively gently, a mass spectrum with few fragments can be obtained. For this reason, it is a particularly useful ionization method for the purpose of obtaining molecular weight information. In general, the chemical ionization method often refers to the case where positive ions are generated based on the principle as described above, but there is also a method of generating negative ions separately from this, which includes the negative chemical ionization method ( NCI).

  As described above, in GC / MS, three types of ionization methods of EI, CI, and NCI are mainly used, and they are properly used according to the purpose of analysis and the type of sample. Since ionization conditions such as gas pressure that can achieve the best ionization efficiency in each ionization method are different, it is desirable to use a dedicated ionization chamber in order to fully exhibit the features of each ionization method (for example, patent documents) 1 etc.). That is, since EI has high ionization efficiency under low gas pressure (high vacuum level) conditions, the sealing degree of the ionization chamber is low, and the sealing degree of the ionization chamber increases in the order of NCI and CI. However, when a dedicated ionization chamber is used for each ionization method, it is necessary to return the inside of the vacuum chamber to almost atmospheric pressure when changing the ionization method, and the ionization chamber needs to be replaced, which is very complicated and poor in analysis efficiency. Become.

Therefore, in recent GC / MS, the ionization chamber combined with each ionization method (hereinafter referred to as EI / CI combined ionization chamber) having a slightly lower sealing degree than the ionization chamber dedicated to CI is used to supply / stop reagent gas. The ionization method is switched only by control such as change in polarity such as applied voltage to each electrode related to switching and ionization. In general, the CI dedicated ionization chamber is used under a gas pressure condition of about 10 ² Pa with the reagent gas introduced. In the case of an EI / CI combined ionization chamber, the gas pressure is one-tenth of the number. It is used under gas conditions as low as 1 / min. Under such a gas pressure condition, although the fragment ions tend to be slightly larger than when using a CI dedicated ionization chamber, it is possible to sufficiently confirm the molecular weight related ions of mass M + 1. The characteristics of CI can be exhibited.

In general, in GC / MS, prior to analysis of an unknown sample, various parameters such as the voltage applied to the lens electrode are adjusted to optimum values using a standard sample whose component type and concentration are known. A function called auto-tuning is provided. Since the mass spectrum pattern of methane, which is a reagent gas for CI, generally depends on the gas pressure conditions in the ionization chamber, the GC / MS adjustment procedure using CI first involves changing the amount of methane introduced into the ionization chamber. However, the peak intensity I ₂₉ of m / z ₂₉ derived from methane and the peak intensity I ₁₇ of m / z ₁₇ are compared, and the amount of methane introduced is determined so that, for example, I ₂₉ / I ₁₇ > 0.2. With the amount of methane introduced fixed to the calculated value, the auto-tuning function is used to set the voltage applied to the lens electrode so that the signal intensity at the m / z specified by the user is maximized. Other conditions are determined.

  However, the pattern of mass spectrum obtained by mass spectrometry using CI does not depend only on the gas pressure in the ionization chamber, but is applied to a repeller electrode disposed in the ionization chamber for extruding ions from the ionization chamber. It depends on the repeller voltage. The repeller voltage is also related to detection sensitivity. According to the study of the present inventor, it has been found that such repeller voltage dependency clearly appears particularly in a CI using an EI / CI combined ionization chamber having a relatively low sealing degree. Therefore, in the GC / MS that performs such CI, even if the parameters such as the lens voltage are determined by the conventional general adjustment procedure as described above, it is not always in a state in which cleavage does not easily occur.

JP 2007-258025 A Jurgen. H Gross, “Mass Spectrometry-Text Book-2004”, Springer, 2004, pp.331-340

  The present invention has been made in order to solve the above-mentioned problems, and the object of the present invention is to appropriately apply a lens voltage or the like so that cleavage is not likely to occur as much as possible when performing ionization by CI, and molecular weight can be easily estimated. It is an object of the present invention to provide a mass spectrometer and an adjustment method thereof.

As described above, in the CI, the reagent gas is first ionized in the ionization chamber, and the sample gas is ionized by causing a chemical reaction between the reagent gas ions and the sample molecules. Therefore, unless a sufficient amount of reagent gas ions are present in the ionization chamber, generation of molecular weight related ions, which is a feature of CI, cannot be performed satisfactorily. When methane is used as the reagent gas, reagent gas ions such as CH ₅ ⁺ that is m / z 17, C ₂ H ₃ ⁺ that is m / z 29, and C ₃ H ₅ ⁺ that is m / z 41 may contribute to CI. It is known (for example, refer nonpatent literature 1).

  Therefore, the inventor of the present application uses the EI / CI combined ionization chamber having a lower hermeticity than the normal CI ionization chamber to determine the relationship between the amount of the various reagent gas ions in the ionization chamber and the repeller voltage. The spectral peaks of the reagent gas ions were experimentally examined by observing them on the mass spectrum. As a result, the signal intensity of the reagent gas ions that can contribute to the CI as described above is maximized when the repeller voltage is in the range of 0 to 1 V, and the signal intensity tends to decrease as the repeller voltage increases. found. In particular, the tendency is remarkable at m / z 41, and it was found that the degree of decrease in the signal intensity is clear when the voltage is made smaller and larger than the repeller voltage showing the maximum signal intensity. Furthermore, the relationship between the detection sensitivity of the benzophenone used as the standard sample and the repeller voltage was also examined, and the behavior was similar to that of the reagent gas ion of m / z 41, and it was found that the sensitivity decreased as the repeller voltage was increased. The present invention has been made based on such experimental findings, and has a feature in a technique for automatically adjusting various parameters of a mass spectrometer.

That is, a mass spectrometer according to the present invention, which has been made to solve the above-described problems, includes an ionization chamber that performs ionization by chemical ionization (CI) therein, and a reagent that introduces methane as a reagent gas into the ionization chamber. A gas introduction unit, a repeller electrode disposed in the ionization chamber for forming an electric field for pushing out the ions generated inside, and the ions released from the ionization chamber for transporting the ions to the mass analysis unit In a mass spectrometer comprising a plurality of lens electrodes,
In order to automatically adjust at least the repeller voltage applied to the repeller electrode and the lens voltage applied to the lens electrode to an optimum state or a state close thereto,
a) Repeller voltage determination for determining the repeller voltage so as to maximize the signal intensity of ions having a mass-to-charge ratio (m / z) of 41 in a state where methane is introduced into the ionization chamber by the reagent gas introduction unit. Means,
b) Lens voltage determining means for determining the lens voltage while maintaining the state where the repeller voltage determined by the repeller voltage determining means is applied to the repeller electrode;
It is characterized by having.

In addition, an adjustment method for a mass spectrometer according to the present invention, which has been made to solve the above-described problems, includes an ionization chamber in which ionization is performed by chemical ionization (CI), and methane is introduced into the ionization chamber as a reagent gas. A reagent gas introduction unit, a repeller electrode disposed in the ionization chamber for forming an electric field for pushing out the ions generated inside, and the ions released from the ionization chamber are transported to the mass analysis unit An adjustment method for automatically adjusting at least a repeller voltage applied to the repeller electrode and a lens voltage applied to the lens electrode to an optimum or close state in a mass spectrometer comprising one or more lens electrodes Because
a) Repeller voltage determination for determining the repeller voltage so as to maximize the signal intensity of ions having a mass-to-charge ratio (m / z) of 41 in a state where methane is introduced into the ionization chamber by the reagent gas introduction unit. Steps,
b) a lens voltage determination step for determining the lens voltage while maintaining the state where the repeller voltage determined in the repeller voltage determination step is applied to the repeller electrode;
It is characterized by performing.

  The mass spectrometer according to the present invention and the adjustment method thereof can be applied to those using an ionization chamber dedicated to CI having a high degree of sealing, but cleavage tends to occur more easily than normal CI. It is particularly useful for those using a CI / EI combined ionization chamber capable of both ionization by CI and ionization by EI.

  When methane is used as the reagent gas, the signal intensity of the reagent gas ion of m / z 41 is clearly dependent on the change of the repeller voltage as described above. The operation of finding the voltage value that maximizes the signal strength can be easily and reliably performed.

  As a result, when ionizing sample molecules, the abundance of reagent gas ions necessary for performing good CI, that is, with little cleavage, is sufficiently secured in the ionization chamber, and the signal intensity of molecular weight related ions is increased. be able to. In particular, according to the mass spectrometer and the adjustment method thereof according to the present invention, CI is performed under conditions where the sealing degree is relatively low and the gas pressure is low (high degree of vacuum), for example, as in the EI / CI combined ionization chamber. Even in this case, it is difficult to cause cleavage, and the signal intensity of molecular weight related ions (proton addition ions) can be increased, thereby providing useful information for estimating the molecular weight.

  A GC / MS which is an embodiment of a mass spectrometer according to the present invention will be described below with reference to the drawings. The GC / MS of this embodiment includes an auto-tuning function for various parameters that employs the method for adjusting a mass spectrometer according to the present invention.

  FIG. 1 is a configuration diagram of a main part of the GC / MS of this embodiment. In the GC unit 1, a sample vaporizing chamber 11 is provided at the inlet end of a capillary column 14 disposed in a column oven (not shown), and He supplied from the carrier gas channel 13 to the sample vaporizing chamber 11 at a substantially constant flow rate. And the like are sent to the capillary column 14. When a small amount of liquid sample is dropped into the heated sample vaporization chamber 11 by the injector 12 at the time of analysis, the liquid sample is immediately vaporized and is sent to the capillary column 14 along the carrier gas flow. The sample components riding on the carrier gas flow are separated and eluted in the time direction when passing through the capillary column 14, and are sent to the MS unit 2 through the flow path switching unit 16.

  In the MS unit 2, an ionization chamber 21, a lens electrode 26, a quadrupole mass filter 27, and an ion detector 28 are disposed in a vacuum chamber 20 that is evacuated by a vacuum pump (not shown). The ionization chamber 21 is an EI / CI combined ionization chamber, to which a reagent gas flow path 22 provided with a valve 23 is connected, and a repeller electrode 24 is installed inside. Although not shown, a filament is attached to the ionization chamber 21, and thermoelectrons generated by the filament are sent into the ionization chamber 21. When ionization by CI is performed, the valve 23 is opened and a reagent gas (in this case, methane) is supplied into the ionization chamber 21, and the reagent gas is ionized by contacting thermal electrons with the reagent gas. The reagent gas ions and sample molecules cause a chemical reaction to generate sample molecule ions, and the generated ions are ionized by the action of an electric field formed by a repeller voltage applied to the repeller electrode 24 from the voltage application unit 33. It is pushed out from the chamber 21 to the right in FIG.

  Ions exiting from the ionization chamber 21 are converged by the action of the electric field formed by the lens electrode 26 and accelerated in some cases, and sent to the quadrupole mass filter 27. A voltage obtained by superimposing a DC voltage and a high frequency voltage is applied to the quadrupole mass filter 27, and only ions having a mass-to-charge ratio (m / z) corresponding to the voltage selectively pass through the filter 27. The ion detector 28 is reached. By changing the voltage applied to the quadrupole mass filter 27 in a predetermined pattern, the mass-to-charge ratio of ions passing through the filter 27 can be scanned within a predetermined range. A detection signal from the ion detector 28 is input to the data processing unit 32, where a mass spectrum is created and quantitative analysis and qualitative analysis are performed. The channel switching unit 16 switches the channel so that a predetermined standard sample prepared in the standard sample introducing unit 40 is introduced into the ionization chamber 21 during automatic adjustment described later. The analysis control unit 31 controls each unit in order to perform analysis, automatic adjustment, and the like. In addition, the central control unit 30 to which the operation unit 36 and the display unit 37 are connected gives instructions to the analysis control unit 31 and the data processing unit 32 in order to comprehensively control each unit in accordance with a predetermined control program, and also performs analysis. Results and the like are displayed on the display unit 37. The central control unit 30 and the data processing unit 32 can realize their functions by executing predetermined control / processing programs on a general-purpose personal computer.

  In the GC / MS of this embodiment, various types of MS unit 2 such as an applied voltage (repeller voltage) to the repeller electrode 24 of the MS unit 2 and an applied voltage (lens voltage) to the lens electrode 26 prior to the analysis of the unknown sample. Characteristic control / processing is executed to adjust the parameters. Control and processing at this time will be described with reference to the flowchart of FIG.

  First, the valve 23 is opened under the control of the analysis control unit 31, and methane as a reagent gas is supplied into the ionization chamber 21 through the reagent gas flow path 22 (step S1). Since the inside of the vacuum chamber 20 is evacuated, methane flows out of the ionization chamber 21 to the outside, so that the inside of the ionization chamber 21 is maintained at a substantially constant gas condition. Next, the person in charge of the analysis inputs auto-tuning conditions (for example, a mass-to-charge ratio for adjusting the lens voltage) through the operation unit 36, and then instructs execution of auto-tuning (step S2). In response to this, the central control unit 30 starts an auto-tuning function (step S3).

  First, a predetermined standard sample prepared in the standard sample introduction unit 40 is introduced into the ionization chamber 21, and the mass-to-charge ratio is calculated based on the position and shape of the spectrum peak appearing on the mass spectrum obtained by mass analysis. Calibration of (m / z), adjustment of the half width of the peak profile, and the like are executed (step S4). This is a normal adjustment work that has been performed conventionally. Thereafter, the voltage applied to the quadrupole mass filter 27 is set so that the ions of the reagent gas ions m / z 41 reach the ion detector 28 without introducing the standard sample into the ionization chamber 21. Then, the voltage value that maximizes the signal strength is searched for while gradually changing the repeller voltage applied to the repeller electrode 24 by the voltage application unit 33 within a predetermined range (for example, −1 to 3 V) (step S5). . As will be described in detail later, at m / z 41, the peak of the change in signal intensity when the repeller voltage is changed appears sharply as compared with other reagent gas ions such as m / z 17 and m / z 29. Therefore, the repeller voltage that maximizes the signal intensity of the reagent gas ions can be determined easily and reliably.

  Next, a predetermined standard sample is introduced into the ionization chamber 21 with the repeller voltage fixed at the voltage value thus determined, and ions having m / z designated by the analyst in step S2 are detected. The voltage applied to the quadrupole mass filter 27 is set so as to reach the vessel 28. The voltage application unit 33 searches for a voltage value that maximizes the signal intensity while gradually changing the lens voltage applied to the lens electrode 26 within a predetermined range. Further, when there is a parameter to be adjusted in addition to the lens voltage, the adjustment is performed here under the same repeller voltage condition (step S6). When necessary parameter adjustment is completed (step S7), the process waits until an analysis instruction or the like is given.

The reason why the m / z 41 is used when determining the repeller voltage as described above and the basis thereof will be described with reference to FIGS.
FIG. 3A shows an EI mass spectrum obtained by actual measurement of methyl stearate, which is generally used to show sensitivity of the mass spectrometer, and FIG. 3B shows a CI mass spectrum obtained by actual measurement. These are the results when EI and CI (reagent gas is methane) are carried out in the EI ionization chamber and the CI ionization chamber, respectively.

  In the EI mass spectrum, there is a base peak with a large signal intensity at m / z 74 (arrow A in the figure), and a peak with a very low signal intensity (arrow B in the figure) can be confirmed for the molecular ion at m / z 298. is there. On the other hand, in the CI mass spectrum, the peak of the proton-added ion [M + H] (arrow C in the figure) appears at m / z 299, which proves very useful for determining the molecular weight. When CI is performed in the EI / CI combined ionization chamber, m / z 299 becomes the base peak as shown in FIG. 3 (b), but tends to be closer to EI than normal CI using the CI dedicated ionization chamber. A peak at m / z 74 is also observed.

FIG. 4 is a diagram showing an intensity ratio I ₂₉₉ / I ₇₄ between the signal intensity I ₂₉₉ with respect to m / z ₂₉₉ and the signal intensity I ₇₄ with respect to m / z ₇₄ when the repeller voltage is changed. The gas pressure condition is 450 Pa. It can be seen that the ratio of I ₂₉₉ is the highest when the repeller voltage is about 0.3 V, and that I ₇₄ becomes relatively stronger as the voltage is increased further. That is, this means that when the repeller voltage is high, cleavage tends to occur. This is presumably because the time required for the sample molecules to sufficiently perform CI in the ionization chamber becomes insufficient as the repeller voltage increases. On the other hand, when the repeller voltage is close to 0 V, the transmittance of light mass ions with a long mean free path in the ionization chamber is relatively improved compared to that of heavy mass ions with a short mean free path, and the signal intensity It can be inferred that the ratio I ₂₉₉ / I ₇₄ is slightly reduced.

FIG. 5A shows an EI mass spectrum of methane itself used as a reagent gas during CI, and FIG. 5B shows a mass spectrum when methane is introduced as a reagent gas into the CI ionization chamber. In the EI mass spectrum, m / z 16 is a base peak (arrow D in the figure), and the peak signal intensity decreases in order of m / z 15 and 14. In contrast, in the CI mass spectrum, there are large peaks (arrow E in the figure) derived from the reagent gas at m / z 17, 29, 41. m / z 17 is CH ₅ ⁺ , m / z 29 is C ₂ H ₅ ⁺ , and m / z 41 is C ₃ H ₅ ⁺ , which are larger than the original sample gas molecules due to the reaction between the reagent gas molecules. It became a mass ion. For example, one proton moves from these reagent gas ions to the sample molecule, thereby generating an ion having a mass of M + 1.

  FIG. 6 is a graph showing the repeller voltage dependence of the signal intensity of each peak in the CI mass spectrum when the EI / CI combined ionization chamber is used. When the repeller voltage is increased, the signal intensity of peaks that are easily observed in EI such as m / z 15 and 16 increases. It can be seen that this agrees with the experimental result for methyl stearate described above that the tendency of EI increases when the repeller voltage is increased. On the other hand, as a general tendency, when the repeller voltage is reduced, the signal intensity of peaks peculiar to CI such as m / z 17, 29, 41, etc. increases. This suggests that there is a high possibility that the reagent gas ions responsible for delivering protons in the CI increase and the sample molecules can be ionized well. That is, the CI under such a condition suggests that a mass spectrum that is good for the sample molecule, that is, has a high peak intensity of molecular weight related ions with little cleavage is obtained.

  FIG. 7 is a graph obtained by normalizing the result of FIG. 6 with 1 having the maximum signal intensity at each m / z. When the change in the signal intensity with respect to the change in the repeller voltage is examined in detail, the maximum is obtained when the repeller voltage is about 0.3 V, and the maximum value is obtained at m / z 41 compared to m / z 17, 29, etc. It can be seen that there is a significant decrease in signal strength when the voltage is away from the applied repeller voltage, that is, the peak is sharp. That is, even with the same reagent gas ion, it can be said that the m / z 41 ion has a remarkable repeller voltage dependency of its signal intensity. As described above, when searching for a voltage value that maximizes the signal intensity while gradually changing the repeller voltage, it is clear that the optimum voltage is more easily found when the peak with respect to the change in the repeller voltage is sharp. For this reason, in the GC / MS of the above embodiment, m / z 41 is used when searching for the optimum repeller voltage.

  The above-described embodiment is an example of the present invention, and it is obvious that modifications and changes can be made as appropriate within the scope of the present invention.

The block diagram of the principal part of GC / MS which is one Example of this invention. The flowchart which shows the characteristic control and process for adjusting the various parameters of MS part in GC / MS which is a present Example. Measured EI mass spectrum (a) of methyl stearate and CI measured mass spectrum (b). It shows the intensity ratio _I 299 _{/ I 74} in the case of changing the repeller voltage. EI mass spectrum of methane (a) and mass spectrum (b) when methane is introduced as a reagent gas into the CI ionization chamber. The graph which shows the repeller voltage dependence of the signal intensity | strength of each peak in CI mass spectrum when an EI / CI combined ionization chamber is used. FIG. 7 is a graph obtained by normalizing the result of FIG. 6 with 1 having the maximum signal intensity at each m / z.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... GC part 11 ... Sample vaporization chamber 12 ... Injector 13 ... Carrier gas flow path 14 ... Capillary column 16 ... Flow path switching part 2 ... MS part 20 ... Vacuum chamber 21 ... Ionization chamber 22 ... Reagent gas flow path 23 ... Valve 24 ... repeller electrode 26 ... lens electrode 27 ... quadrupole mass filter 28 ... ion detector 30 ... central control unit 31 ... analysis control unit 32 ... data processing unit 33 ... voltage application unit 36 ... operation unit 37 ... display unit 40 ... standard Sample introduction part

Claims (4)

An ionization chamber that performs ionization by chemical ionization (CI) therein, a reagent gas introduction unit that introduces methane into the ionization chamber as a reagent gas, and an ion generated inside that is disposed in the ionization chamber to the outside In a mass spectrometer comprising: a repeller electrode for forming an electric field to be pushed into the ion source; and one or a plurality of lens electrodes for transporting ions released from the ionization chamber to a mass analyzer.
In order to automatically adjust at least the repeller voltage applied to the repeller electrode and the lens voltage applied to the lens electrode to an optimum state or a state close thereto,
a) Repeller voltage determination for determining the repeller voltage so as to maximize the signal intensity of ions having a mass-to-charge ratio (m / z) of 41 in a state where methane is introduced into the ionization chamber by the reagent gas introduction unit. Means,
b) Lens voltage determining means for determining the lens voltage while maintaining the state where the repeller voltage determined by the repeller voltage determining means is applied to the repeller electrode;
A mass spectrometer comprising:   2. The mass spectrometer according to claim 1, wherein the ionization chamber combines ionization by chemical ionization (CI) and ionization by electron ionization (EI). An ionization chamber that performs ionization by chemical ionization (CI) therein, a reagent gas introduction unit that introduces methane into the ionization chamber as a reagent gas, and an ion generated inside that is disposed in the ionization chamber to the outside In a mass spectrometer comprising: a repeller electrode for forming an electric field to be pushed out to the surface; and one or a plurality of lens electrodes for transporting ions released from the ionization chamber to a mass analyzer, and applied to at least the repeller electrode An adjustment method for automatically adjusting a repeller voltage and a lens voltage applied to the lens electrode to an optimum state or a state close thereto,
a) Repeller voltage determination for determining the repeller voltage so as to maximize the signal intensity of ions having a mass-to-charge ratio (m / z) of 41 in a state where methane is introduced into the ionization chamber by the reagent gas introduction unit. Steps,
b) a lens voltage determination step for determining the lens voltage while maintaining the state where the repeller voltage determined in the repeller voltage determination step is applied to the repeller electrode;
A method for adjusting a mass spectrometer, characterized in that   4. The method of adjusting a mass spectrometer according to claim 3, wherein the ionization chamber combines ionization by chemical ionization (CI) and ionization by electron ionization (EI). Device adjustment method.

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