JP6508215B2 - Mass spectrometer - Google Patents

Description

  The present invention relates to a mass spectrometer, and more particularly to a mass spectrometer equipped with an ion source by electron ionization.

  A mass spectrometer is an apparatus that separates and detects ionized sample molecules according to mass-to-charge ratio (m / z), detects an ion source for ionizing sample molecules, and generates generated ions to mass-to-charge ratio. A mass separation unit that separates in response, and an ion detector that sequentially detects separated ions are provided. Various methods have been devised as methods for ionizing sample molecules and atoms, but in the case where a gaseous sample is ionized as in a gas chromatograph mass spectrometer (GC-MS) combining a gas chromatograph and a mass spectrometer Generally, an electron ionization (EI = Electron Ionization, also referred to as electron impact ionization) method is used.

  In an ion source performing ionization by electron ionization, sample molecules are introduced into a relatively small volume ionization chamber placed under a vacuum atmosphere, and a heating current is supplied to a filament disposed outside the ionization chamber. Thermions are emitted from the filament. An electric field having a potential gradient due to the potential difference between the filament and the ionization chamber is formed in the space between the filament and the ionization chamber, and the thermal electrons emitted from the filament are accelerated toward the ionization chamber by the electric field and provided on the wall of the ionization chamber. Enters the ionization chamber through the electron inlet. In the electron ionization method, the potential difference between the filament and the ionization chamber is usually set to about 70 V in order to provide the thermal electrons with acceleration energy of about 70 eV.

When the thermionic electron (e ⁻ ) that has entered the ionization chamber contacts the sample molecule (M), the molecular ion of the sample (hereinafter referred to as “sample ion”) M ^{+ as} M + e ⁻ → M ⁺ + 2 e ⁻ Is generated. The sample ions M ⁺ thus generated are extracted from the ionization chamber through the ion emission port to the outside by the electric field formed by the extraction electrode provided outside the ionization chamber.

In GC-MS, which is a combination of a gas chromatogram and a mass spectrometer, the sample is mixed with a carrier gas, which is a rare gas (usually using He), introduced into a gas chromatograph, and separated by a gas chromatograph column. It is introduced into the ionization chamber of the analyzer. At this time, in the ionization chamber, the sample molecules are ionized by the contact with the above-mentioned thermal electrons, and at this time, the He gas flowing into the ionization chamber together with the sample molecules is also ionized or excited in contact with the thermal electrons. Here, when He is ionized, He ⁺ (helium ion) is generated, and when He is excited to a long-lived metastable state at an energy level higher than the ground state, He ^* (metastable helium) is generated. It is generated.

He ⁺ and He ^* generated from He become background components that can not be ignored when performing high sensitivity analysis in a mass spectrometer, and cause a decrease in S / N ratio. However, among the background from He, due to He ^+, by providing a suitable electromagnetic field in the ion transport optical system and the mass separation section provided downstream of the ion source, He ⁺ ion detector It is possible to remove before reaching.

On the other hand, He ^* is electrically neutral and can not be removed by an electromagnetic field. He ^* entering from the ionization chamber to the ion transport optical system and mass separation unit at the latter stage acts as a carrier carrying energy, interacts with surrounding atoms and molecules, and causes ionization phenomenon. For example, when He ^* interacts with the surface atoms of the metal component constituting the ion transport optical system or the mass separation unit, He ^* gives electrons to the metal surface atoms to become He ⁺ . Such a phenomenon is called resonance ionization. In addition, when He ^* interacts with an insulator such as residual gas (X) in the apparatus, the counter atom (molecule) is ionized to generate X ⁺ . Such a phenomenon is called Penning ionization. That is, the background due to the He ^*, the He ^* themselves not only those caused by reaching the ion detector, the He ^* from a secondary generated by He ⁺ and X ⁺ is an ion detector Some are caused by being detected.

Therefore, GC-MS equipped with a mechanism for discharging He ^* from the ionization chamber has been proposed as a device for reducing such background (Patent Document 1). This is to add an opening for exhaustion in the ionization chamber and to provide a pressure difference between the ionization chamber and the outside by the vacuum pump connected to the opening, and the pressure difference formed by the vacuum pump makes He ^* The gas is discharged from the opening to the outside of the ionization chamber. As a result, He ^* is removed from the inside of the mass spectrometer without entering the ion transport optical system or the mass separation unit, so that the generation of background derived from He ^* can be suppressed.

Unexamined-Japanese-Patent No. 2006-189299

  The above method requires the ion source to be provided with a new opening and a vacuum pump, which requires a significant change in the apparatus configuration. Therefore, there is a problem that the manufacturing cost of the device is increased.

  In addition, the metastable state exists also in noble gases other than He, and the same problem arises when using these as a carrier gas of GC-MS. Further, not only GC-MS, but also when the sample gas mixed with the carrier gas is directly introduced into the mass spectrometer, the same problem as described above occurs.

  The present invention has been made in view of the above-described point, and the purpose of the present invention is to effectively generate the background derived from a carrier gas such as He without largely changing the configuration of the ion source. It is an object of the present invention to provide a mass spectrometer which can be reduced.

The mass spectrometer according to the present invention, which was made to solve the above problems,
a) a filament that generates thermoelectrons,
b) A sample inlet into which a sample gas is introduced, and an electron inlet into which the thermoelectrons generated by the filament are introduced, and the sample gas introduced from the sample inlet and the electron inlet, respectively An ionization chamber for ionizing the sample gas by bringing the thermal electron and the thermal electron into contact with each other;
c) potential difference generation means for generating a potential difference between the filament and the ionization chamber;
d) a first state in which the potential of the filament is lower than the potential of the ionization chamber by controlling the potential difference generation means, and a potential of the filament which is the same as or higher than the potential of the ionization chamber State switching means for switching between two states;
It is characterized by having.

In such a configuration, in the first state, since the potential of the filament is lower than the potential of the ionization chamber, thermoelectrons having a negative charge are accelerated from the filament toward the ionization chamber to introduce the electrons. It is introduced into the ionization chamber from the mouth. As a result, sample molecules (M) in the sample gas introduced from the sample inlet contact the thermionic electron (e ⁻ ) introduced from the electron inlet in the inside of the ionization chamber, and the sample ion M ⁺ It is generated. At this time, a carrier gas introduced into the ionization chamber together with the sample gas, for example, He gas is also ionized or excited in contact with the thermions in the ionization chamber to generate helium ions He ⁺ and metastable helium molecules He ^*. Ru.

Among the ions generated in the ionization chamber and the molecules in the metastable state, the sample ion M ⁺ or helium He ⁺ having a charge has the function of an electric field formed by an extraction electrode or the like provided downstream of the ionization chamber. It is quickly withdrawn to the outside and is led to an ion detector through a mass separation unit. Furthermore, for these He ^+, by providing the appropriate electromagnetic field in the subsequent stage as the ionization chamber of the above (ion transport optical system and the mass separation unit), it is removed before the He ⁺ reaches the ion detector Can.

On the other hand, since the helium molecule He ^{* in the} metastable state has no charge, it is not extracted from the ionization chamber by the electric field formed by the extraction electrode or the like. However, in general, the pressure inside the mass spectrometer is gradually lowered from the space in which the ion source is disposed to the space in which the detector is disposed by differential pumping using a plurality of vacuum pumps. Because of this pressure difference, He ^* gradually moves out of the ionization chamber. Then, part of the He ^{* which} has moved from the ionization chamber to the outside and the undesired ions X ⁺ generated secondarily from the He ^* are discharged to the outside of the mass spectrometer by the vacuum pump. The remaining part reaches the ion detector and is detected. That is, immediately after the mass spectrometer according to the present invention is in the first state, only the sample ion M ⁺ reaches the ion detector, and then, after a certain time, the He ^* and X ⁺ ions become the ion detector. It will reach.

On the other hand, in the second state, since the potential of the filament is equal to or higher than the potential of the ionization chamber, the force for accelerating the thermoelectrons generated by the filament to the ionization chamber is lost. Therefore, the thermoelectrons are not introduced into the ionization chamber, and the sample ions M ⁺ , helium ions He ⁺ and metastable helium He ^* are not generated in the ionization chamber. Therefore, when the mass spectrometer according to the present invention is switched from the first state to the second state, the sample ion M ⁺ is not detected by the ion detector, is generated during the first state, and remains in the device. Only He ^* and unwanted ions X ⁺ derived from it can be detected by the ion detector. However, during the second state without new the He ^* is generated, to be discharged to gradually outside by the He ^* also the vacuum pump which have remained in the system, switched to the second state As time passes, the number of He ^* and X ⁺ reaching the ion detector gradually decreases.

Therefore, mass analysis of the sample is performed while alternately switching the first state and the second state, and a mass is obtained using only the signal obtained in the first state among the signals acquired by the detector during that time. If a spectrum is generated, it is possible to obtain a mass spectrum derived only from the sample component, which is not affected by noise derived from He ^* .

That is, the mass spectrometer according to the present invention is
Furthermore,
e) control means for controlling the state switching means to alternately repeat the first state and the second state while performing mass spectrometry on one sample;
f) ion extracting means for extracting the ions generated in the ionization chamber to the outside of the ionization chamber;
g) a mass separation unit for separating the ions extracted from the ionization chamber by the ion extracting means based on mass-to-charge ratio;
h) a detector that detects ions of the ions that have passed through the mass separation unit;
i) a data processing unit that generates a mass spectrum of the sample using a signal acquired in the first state among detection signals acquired by the detector during mass analysis of the one sample;
It is possible to have

  Here, "during mass analysis of one sample" means from the start to the end of mass analysis accompanying one sample introduction to the mass spectrometer or a gas chromatograph connected to the front stage of the mass spectrometer. Means time.

In the configuration as described above, the control means switches to the second state, for example, when a predetermined time A has elapsed since the start of the first state, and then a predetermined time B has elapsed. The operation of switching to the first state may be repeatedly performed at a point in time. The time A is, for example, based on the time from the start of the first state in the mass spectrometer to the time when a noise component derived from He ^* or the like is detected. It can be determined in advance. In addition, the time B may be determined in advance based on the time by examining the time from when the second state is started in the mass spectrometer to when noise derived from He ^* is not detected. Can.

Alternatively, the control means may determine the timing of switching the first state and the second state based on the detection signal from the detector. In this case, for example, after the start of the first state, the total value of detection signals obtained during that time is determined every fixed time (for example, every time one mass scan is completed), and the total value immediately after the start of the first state Is switched to the second state at a point when it increases to some extent from the value of (that is, when the influence of noise derived from He ^* or the like becomes rather large). Then, after the start of the second state, (the time when the influence of noise is decreased to a certain extent derived i.e. the He ^*) the total value of the detection signal for each predetermined time point to some extent decreased from the value immediately after the start of the second state It is conceivable that switching to the first state is performed.

  By performing the control as described above, the detection signal obtained by the detector in the first state can be made substantially free of He-derived noise.

Further, the mass spectrometer according to the present invention is
The mass separation portion, be one which scans the mass-to-charge ratio of ions passing the mass fraction away portion at a fixed period,
It is preferable that the control means performs switching from the second state to the first state in accordance with a predetermined timing of the cycle by the mass separation unit.

  Thereby, a specific timing of mass scanning in the mass separation unit (for example, simultaneous with the start of each mass scanning, or any time between one mass scanning being completed and the next mass scanning being started) Ions can be efficiently introduced into the detector by switching from the second state to the first state.

Alternatively, the mass spectrometer according to the present invention is
Furthermore,
e) control means for controlling the state switching means to perform switching from the first state to the second state at least once while performing mass spectrometry on one sample;
f) ion extracting means for extracting the ions generated in the ionization chamber to the outside of the ionization chamber;
g) a mass separation unit for separating the ions extracted from the ionization chamber by the ion extracting means based on mass-to-charge ratio;
h) a detector that detects ions of the ions that have passed through the mass separation unit;
i) the sample obtained by subtracting the signal obtained in the second state from the signal obtained in the first state among detection signals obtained by the detector during mass analysis of the one sample A data processing unit that generates a mass spectrum of
It is also possible to have

As described above, in the mass spectrometer according to the present invention, only the sample ion M ⁺ reaches the detector immediately after the first state is started, but then, after a certain amount of time has elapsed, He ^* or the undesired source thereof Ion X ^{+ will} also reach the detector. Therefore, if the first state is continued for a certain period of time, the detection signal obtained during the first state includes the signal derived from the sample ion M ⁺ and the noise component derived from He ^* and X ⁺ It becomes a thing. Further, as described above, when the mass spectrometer according to the present invention is switched from the first state to the second state, the sample ion M ⁺ is not detected by the detector immediately after that but He ^* and X ⁺ are for a while Meanwhile, the detector is reached and detected, and then gradually not detected. Therefore, by setting the execution time of the second state to an appropriate length, the detection signal obtained during the second state can be made up of noise components derived substantially from He ^* and X ⁺ only. .

  Therefore, as described above, by subtracting the signal obtained in the second state from the signal obtained in the first state in the data processing unit, the influence of the noise component can be removed, and only the sample component can be removed. It is possible to obtain a mass spectrum derived from

  The data processing unit first subtracts the detection signal obtained in the second state from the detection signal obtained in the first state, and then generates a mass spectrum of the sample based on the signal after the subtraction. Alternatively, first, a mass spectrum is generated from the detection signal obtained in the first state and a mass spectrum is generated from the detection signal obtained in the second state, and then the latter is generated from the mass spectrum of the former. The mass spectrum of the sample may be generated by subtracting the mass spectrum of

The mass spectrometer according to the present invention is
The potential difference generation means applies a DC bias voltage to the filament or the ionization chamber so as to accelerate the thermoelectrons generated in the filament toward the ionization chamber.
The state switching means may switch between the first state and the second state by switching on / off of voltage application by the potential difference generation means.

  The mass spectrometer according to the present invention is applicable not only to the case where He is used as a carrier gas as described above, but also to the case where another noble gas is used as a carrier gas.

  As described above, according to the mass spectrometer of the present invention, it is possible to effectively reduce the generation of the background derived from the carrier gas such as He without largely changing the configuration of the ion source.

BRIEF DESCRIPTION OF THE DRAWINGS The principal part block diagram of the GC-MS system provided with the mass spectrometer which concerns on one Embodiment of this invention. The schematic diagram which shows the structure of the ion source in the embodiment. The flowchart which shows an example of the analysis procedure of the sample in the embodiment. The flowchart which shows another example of the analysis procedure of the sample in the embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a GC-MS system including a mass spectrometer according to the present embodiment. The GC-MS system includes a GC unit 100, an MS unit 300, and a control / processing unit 400 for controlling the operation of the unit and processing measurement data obtained by the MS unit 300. .

  In the GC unit 100, a carrier gas such as helium is supplied to the column 130 through the sample vaporization chamber 110 at a constant flow rate. When a small amount of sample is injected from the injector 120 into the sample vaporization chamber 110 at a predetermined timing according to an instruction from the control / processing unit 400, the sample is instantaneously vaporized and introduced into the column 130 on the carrier gas flow. . Then, while the sample passes through the column 130 temperature-controlled by the column oven 140, various components contained in the sample are separated and flow out from the outlet of the column 130 with time lag.

  The sample gas flowing out of the column 130 is introduced into the ion source 320 of the MS unit 300 through the interface unit 200 provided between the GC unit 100 and the MS unit 300. Component molecules contained in the sample gas are ionized in the ion source 320 by electron ionization. The generated ions are extracted to the outside of the ion source 320 by the electric field generated by the extraction electrode 330, focused by the ion transport optical system 340, and introduced into the mass separation unit 350. A voltage obtained by superimposing a DC voltage and a high frequency voltage (RF voltage) is applied to a quadrupole mass filter 351 provided in the mass separation unit 350, and a specific mass-to-charge ratio (m / z) according to the applied voltage. Only the ions having y pass through the space, are converged by the pre-detector ion lens 360, and reach the detector 370 to be detected. A detection signal from the detector 370 is converted into digital data by the A / D converter 371 and input to the control / processing unit 400.

  The voltage applied to the quadrupole mass filter 351 is repeatedly scanned within a predetermined voltage range under the control of the control / processing unit 400. Thereby, in the MS unit 300, scan measurement of a predetermined mass-to-charge ratio range is repeatedly performed on the sample gas sequentially introduced from the GC unit 100 with the passage of time, and the control / processing unit 400 Data having dimensions of time, signal strength are input. The ion source 320, the ion transport optical system 340, the quadrupole mass filter 351, the pre-detector ion lens 360, and the detector 370 described above are in the vacuum chamber 310 vacuum-sucked by the vacuum pumps 311, 312, 313. Are located in By differential pumping using these vacuum pumps 311, 312, 313, the vacuum chamber 310 is gradually evacuated from the space in which the ion source 320 is disposed toward the space in which the detector 370 is disposed. It is configured to be high.

  The substance of the control / processing unit 400 is a computer such as a personal computer provided with a CPU, a memory, and a large-capacity storage device such as an HDD, and in this computer, a user (person in charge of analysis) inputs analysis conditions and the like. An operation unit 430 formed of a keyboard, a pointing device such as a mouse, and a display unit 440 formed of a liquid crystal display or the like are connected. The control / processing unit 400 further includes an analysis control unit 410 and a data processing unit 420 as functional blocks. These are all functional units that are realized as software by the CPU built in the computer reading out dedicated control and processing software pre-installed in the computer to the memory and executing the software.

  Subsequently, the configuration of the ion source 320, which is a characteristic element of the present invention, will be described in detail. FIG. 2 is a schematic view showing the configuration of the ion source 320 in the GC-MS system of FIG. The ion source includes an ionization chamber 321 for ionizing a sample inside, a filament 322 generating thermal electrons, and a trap electrode 323 (target or electron collector for collecting thermal electrons having passed through the ionization chamber 321). And).

  A sample introduction tube 210 is connected to one wall of the ionization chamber 321 disposed in a vacuum atmosphere, and the sample containing the sample molecules to be analyzed that has reached the MS unit 300 from the GC unit 100 via the interface unit 200. Gas is introduced into the ionization chamber 321 through the sample introduction tube 210. Furthermore, in the ionization chamber 321, an electron inlet 321a is formed in one of two wall surfaces positioned in a direction (vertical direction in the figure) substantially orthogonal to the introduction direction of the sample gas, and an electron outlet 321b is formed in the other. Among them, the filament 322 is disposed outside the electron inlet 321a, and the trap electrode 323 is disposed outside the electron outlet 321b. Further, an ion outlet 321 c for extracting the ions generated in the ionization chamber 321 to the outside is formed on another wall surface of the ionization chamber 321.

  A heating current source 324 is connected to the filament 322, and when a heating current is supplied from the heating current source 324 to the filament 322, the temperature of the filament 322 rises and thermal electrons are emitted. Further, the filament 322 is connected to the first bias voltage source 326 (corresponding to potential difference generation means in the present invention) via the switch 325 (corresponding to the state switching means in the present invention), and the switch 325 is closed (ON state ), The filament 322 is biased by the first bias voltage source 326 to a negative potential (e.g. -70 V). Further, the ionization chamber 321 is grounded, and the trap electrode 323 is biased to a positive potential (for example, 10 V) by the second bias voltage source 327.

As described above, in the state where the switch 325 is turned on (hereinafter referred to as the “first state”), the potential of the filament 322 is −70 V, and the potential of the ionization chamber 321 is 0 V. Therefore, the thermoelectrons generated in the filament 322 are accelerated by this potential difference and enter the ionization chamber 321 through the electron inlet 321a. When the thermoelectrons (e ⁻ ) contact the sample molecules (M) in the ionization chamber 321, sample ions M ⁺ are generated as M + e ⁻ → M ⁺ + 2 e ⁻ . At this time, thermions also contact the molecules of the carrier gas (He) introduced into the ionization chamber 321 together with the sample molecules, and helium ions He ⁺ and metastable helium molecules He ^* are generated. The positive ions (M ⁺ and He ⁺ ) generated in the ionization chamber 321 as described above are extracted to the outside of the ionization chamber 321 through the ion outlet 321 c by the electric field formed by the extraction electrode 330 (shown only in FIG. 1). Be On the other hand, the potential difference formed between the ionization chamber 321 and the trap electrode 323 (0 V at the ionization chamber 321 side and 10 V at the trap electrode 323 side) is generated by the generation of thermal electrons and positive ions as described above. To the trap electrode 323 through the electron exit 321b. Thus, a trap current flows in the trap electrode 323. The trap electrode 323 is connected to a current detection unit 328 for detecting the trap current, and a detection signal from the current detection unit 328 is converted into digital data by the A / D converter 329 and input to the control / processing unit 400. Be done. Since the number of electrons trapped by the trap electrode 323 depends on the number of electrons emitted from the filament 322, the feedback control of the heating current source 324 so that the trap current becomes constant generates generation of thermal electrons in the filament 322. The amount can be maintained substantially constant to stabilize the ionization in the ionization chamber 321.

On the other hand, in the state where the switch 325 is turned off (hereinafter referred to as the “second state”), no bias voltage is applied from the first bias voltage source 326 to the filament 322, so the potential of the filament is in the ionization chamber 321. It becomes almost equal to the potential (0 V). As a result, since the force of accelerating the thermoelectrons generated by the filament 322 into the ionization chamber 321 is lost, the thermoelectrons are not introduced into the ionization chamber 321. Therefore, ionization of sample molecules and carrier gas molecules as described above is not performed, and sample ions M ⁺ and helium ions He ⁺ are not generated. The sample gas and the carrier gas introduced into the ionization chamber 321 during this time are gradually discharged to the outside of the vacuum chamber 310 by the actions of the vacuum pumps 311, 312, and 313.

  Also during the second state (that is, while the application of the bias voltage from the first bias voltage source 326 to the filament 322 is stopped), the supply of the heating current to the filament 322 by the heating current source 324 continues. This is because the temperature of the filament 322 is lowered by stopping the supply of the heating current, and when the supply of the heating current and the introduction of the thermions into the ionization chamber 321 are resumed, the thermoelectrons from the filament 322 To prevent the occurrence of Since the thermoelectrons do not reach the trap electrode 323 while the introduction of the thermoelectrons to the ionization chamber 321 is stopped, the feedback control of the heating current source 324 based on the detected value of the trap current as described above is performed. It is not possible. Therefore, during this time, for example, the control of the heating current source 324 is performed based on the value of the trap current detected by the current detection unit 328 immediately before switching the switch 325 from ON to OFF (that is, just before turning OFF the switch). Keep supplying the same heating current).

  Hereinafter, an example of the analysis procedure of the sample using the GC-MS system according to the present embodiment will be described with reference to the flowchart of FIG.

  First, when the user instructs the control / processing unit 400 to start analyzing a sample by GC-MS by performing a predetermined operation using the operation unit 430, the analysis control unit 410 controls the injector 120 of the GC unit 100. Then, a sample is introduced into the flow of the carrier gas in the GC unit 100 (step S11). Thereafter, when it is about time the sample component starts to flow out of the column 130 after a certain amount of time, mass analysis (scan measurement in a predetermined mass-to-charge ratio range) by the MS unit 300 is started under the control of the analysis control unit 410. (Step S12). At the start of mass spectrometry, the MS unit 300 is in the first state (step S13), and the thermoelectrons generated by the filament 322 are in a state of being introduced into the ionization chamber 321. Then, when a predetermined time A has elapsed from the time when the first state is started (that is, when Yes in step S14), the switch 325 is turned off under the control of the analysis control unit 410. The state is switched to the second state (step S15). Note that, during the first state and the second state described above, scan measurement by the MS unit 300 is repeatedly performed at fixed time intervals. After that, when a predetermined time B has elapsed from the start of the second state (that is, when Yes in step S16), the switch 325 is turned on under the control of the analysis control unit 410 to start from the second state Switching to the first state is performed (step S13).

In the above, since the thermoelectrons are introduced into the ionization chamber 321 in the first state, the sample gas and the carrier gas introduced into the ionization chamber 321 from the sample introduction tube 210 are ionized by contact with the thermoelectrons. These ions, ie, the above-described sample ions M ⁺ and helium ions He ⁺ are immediately accelerated by the extraction electrode 330 and extracted from the ionization chamber 321 through the ion outlet 321 c. Then, the helium ion He ⁺ is removed by applying an appropriate electromagnetic field in the ion transport optical system 340 or the mass separation unit 350, and only the sample ion M ⁺ passes through the mass separation unit 350 and is detected by the detector 370 Be done.

On the other hand, this time helium molecules the He ^* also metastable state by the contact of the ionization chamber 321 in the carrier gas and the thermal electrons are generated, said the He ^* or undesired ions X that occur due to it ^{+ (hereinafter,} "the He ^* A portion of “etc.” is also detected by the detector 370. However, since He ^* is electrically neutral, it is not extracted from the ionization chamber 321 by the extraction electrode 330, and gradually moves from the ionization chamber 321 to the outside according to the pressure difference in the vacuum chamber 310. Therefore, there is a certain time difference from when the first state is started until He ^{* and the} like reach the detector 370. Therefore, for example, by obtaining the time difference in advance and setting the time which is sufficiently shorter than the time difference as the predetermined time A, the first state to the second state before He ^{* and the} like start to reach the detector 370 You can switch to Therefore, the detection signal output from the detector 370 during the period from Step 13 to Step S14 described above can be regarded as originating only from the sample ion M ⁺ . In this example, it is necessary to perform scan measurement by the MS unit 300 at least once while continuing the first state. Therefore, the time A is longer than the execution time of one scan measurement.

On the other hand, in the second state, since the thermal electrons are not introduced into the ionization chamber 321, none of the sample ions M ⁺ , helium ions He ⁺ , and metastable helium He ^* are generated. As described above, since the M ⁺ generated in the first state immediately reaches the detector 370 and detected, the detection signal output from the detector 370 in the second state is generated in the first state and the vacuum is generated. It is considered to be derived from He ^* or the like remaining in the chamber 310. However, since He ^{* and the} like remaining in the vacuum chamber 310 are gradually discharged out of the vacuum chamber 310 by the vacuum pumps 311, 312, 313, these are also gradually not detected by the detector 370. Therefore, the time from when the second state is started to when He ^* etc. is not detected by detector 370 is determined in advance, and by setting the time as the predetermined time B, the influence of He ^* etc. disappears. It is possible to quickly switch from the second state to the first state when the

  Steps S13 to S17 are repeatedly executed until a predetermined time elapses from the sample introduction (step S11) to the GC unit 100 (that is, until Yes in step S17). When the result in step S17 is YES, mass spectrometry by the MS unit 300 is stopped (step S18), and then data processing by the data processing unit 420 is executed. That is, based on each of the detection signals obtained in the plurality of first states performed from the start (step S12) to the end (step S18) of mass spectrometry, the horizontal axis represents the mass-to-charge ratio, and the vertical axis A plurality of mass spectra whose intensities have been obtained are generated (step S19).

  The plurality of mass spectra correspond to the components eluted from the column 130 of the GC unit 100 at each time between the steps S12 to S18, and the data processing unit 420 further generates the plurality of mass spectra from the plurality of mass spectra. A chromatogram for the sample is generated. For example, the intensity of ions of a predetermined mass-to-charge ratio (or the maximum value or the total value of the ion intensities in a predetermined mass-to-charge ratio range) on each mass spectrum is taken on the vertical axis, and time (retention time) is on the horizontal axis By taking it, a chromatogram of the sample can be generated. The generated mass spectrum and chromatogram can be displayed on the screen of the display unit 440 when the user performs a predetermined operation from the operation unit 430.

As described above, in this example, scan measurement in the MS unit 300 is repeatedly performed while alternately switching between the first state and the second state during execution of sample analysis in the GC-MS system. Then, among the detection signals obtained by the scan measurement, only the detection signal obtained during the first state is used for generation of a mass spectrum. As described above, since the detection signal obtained in the first state in this example is substantially derived only from the sample ion M ⁺ , this obtains a mass spectrum that does not include the influence of noise derived from He ^* or the like. be able to.

In the above example, after the ion source 320 is switched to the second state, switching to the first state is performed immediately when a predetermined time B has elapsed, but instead of this, the time B is changed. It is desirable that the switching from the second state to the first state be performed when a predetermined timing of mass scanning in the mass separation unit 351 comes after the elapse of. Thereby, the sample ions M ⁺ generated in the ionization chamber 321 can efficiently reach the detector 370 in the first state. In this case, the “predetermined timing of mass scanning” is switched from the second state to the first state at various timings of mass scanning while introducing the sample gas directly to the MS unit 300 in advance. This can be determined by examining the timing when the intensity of the sample ion M ⁺ detected by the detector 370 in the state becomes the largest.

  Subsequently, another example of the analysis procedure of the sample using the GC-MS system according to the present embodiment will be described with reference to the flowchart of FIG. 4.

  First, when the user instructs the control / processing unit 400 to start analyzing a sample by GC-MS by performing a predetermined operation using the operation unit 430, the analysis control unit 410 controls the injector 120 of the GC unit 100. Then, the sample is introduced into the flow of the carrier gas in the GC unit 100 (step S21). Thereafter, when it is about time when a certain amount of time passes and sample components start to flow out of the column 130, mass analysis (mass scan in a predetermined mass-to-charge ratio range) by the MS unit 300 is started under the control of the analysis control unit 410. (Step S22). At the start of the mass analysis, the MS unit 300 is brought into the first state (step S23), and thermions generated by the filament 322 are introduced into the ionization chamber 321. Then, when a predetermined time A 'has elapsed from the time when the first state is started (that is, when Yes in step S24), the switch 325 is turned off under the control of the analysis control unit 410. Switching from the 1 state to the second state is performed (step S25). Note that, during the first state and the second state described above, scan measurement by the MS unit 300 is repeatedly performed at fixed time intervals.

As described above, in the first state, sample ions M ⁺ , helium ions He ^+, metastable helium molecules He ^{* and the} like are generated in the ionization chamber 321. Among these, sample ions M ⁺ and helium ions He ⁺ having positive charges are immediately extracted to the outside of the ionization chamber 321 through the ion exit 321 c by the action of the extraction electrode 330. Among these, the helium ion He ⁺ is removed by applying an appropriate electromagnetic field by the ion transport optical system 340 and the mass separation unit 350, so that only the sample ion M ⁺ is detected by the detector 370. On the other hand, He ^* and undesired ions X ⁺ (hereinafter referred to as “He ^* etc.”) generated due to the He ^* or the like are generated from the time when the first state is started until they reach the detector. Time is required. Therefore, for example, this time is obtained in advance, and a time sufficiently longer than the time is set as the predetermined time A ′. Thereby, the detection signal output from the detector 370 in the first state can include both the signal derived from the sample ion M ⁺ and the signal of the noise component derived from He ^* or the like.

On the other hand, in the second state, since thermal electrons are not introduced into the ionization chamber, none of the sample ions M ⁺ , helium ions He ⁺ , and metastable helium He ^* are generated. As described above, since the M ⁺ generated in the first state immediately reaches the detector 370 and detected, the detection signal output from the detector 370 in the second state is generated in the first state and vacuumed. It can be considered as originating from He ^* or the like remaining in the chamber 310. However, since He ^{* and the} like remaining in the vacuum chamber 310 are gradually discharged out of the vacuum chamber 310 by the vacuum pumps 311, 312, 313, these are also gradually not detected by the detector 370. Therefore, a time from when the second state is started to when He ^{* and the} like are not detected by the detector 370 is determined in advance, and a time sufficiently shorter than the time is set as the predetermined time B '. As a result, the detection signal output from the detector 370 in the second state can be regarded as consisting only of the signal of the noise component derived from He ^* or the like. In this example, it is necessary to perform scan measurement by the MS unit 300 at least once while continuing the first state and continuing the second state. Therefore, both the time A ′ and the time B ′ are set longer than the execution time of one scan measurement. The following description will be made on the assumption that the time A ′ and the time B ′ are both long enough to perform scan measurement a plurality of times.

  After that, when a predetermined time B 'has elapsed from the start of the second state (that is, when Yes in step S26), mass spectrometry by the MS unit 300 is stopped under the control of the analysis control unit 410 ( Step S27).

  Here, the time required from the introduction of the sample to the GC unit 100 to the end of the analysis (for example, the time until all of the sample components separated by the GC unit 100 reach the MS unit 300) is determined in advance. And let this time be the execution time C of the sample analysis by this GC-MS system, and the relation between the execution time C and the above time A ′ and time B ′ is such that A ′ + B ′ = C. Set 'and B'.

  As described above, when sample analysis by GC-MS is completed, data processing by the data processing unit 420 is subsequently performed. That is, first, from detection signals obtained by a plurality of scan measurements performed during the first state (that is, from Step S23 to Step S24, Yes), each of the ongoing states of the first state is obtained. Mass spectra at time are respectively generated (step S28). Subsequently, from the detection signals obtained by a plurality of scan measurements performed during the second state (that is, from Step S25 to Step S26 when Yes), each of the ongoing states of the second state is obtained. A mass spectrum at time is generated (step S29). Then, among the mass spectra generated in step S29, a suitable one, for example, one having the largest total value of ion intensities is determined as a subtraction spectrum, and the subtraction is performed from each of the plurality of mass spectra obtained in step S28. Spectrum for the current spectrum is subtracted (step S30).

As described above, the detection signal obtained in the first state in this example includes both the signal derived from the sample ion M ⁺ and the signal of the noise component derived from He ^* or the like. Therefore, each mass spectrum (produced in step S28) generated based on the detection signal also includes both the peak derived from M ⁺ and the peak derived from He ^* or the like. On the other hand, since the detection signal obtained in the second state consists only of the signal of the noise component derived from He ^* etc., the mass spectrum generated on the basis of the detection signal (generated at step S29) Also, only the peak derived from He ^* etc. is included. Therefore, by subtracting the mass spectrum generated in step S29 from each of the plurality of mass spectra generated in step S28 as described above, the influence of noise components can be removed from the plurality of mass spectra, A mass spectrum can be obtained which contains only the peaks of the sample ion M ⁺ .

  Each of the mass spectra after subtraction obtained above corresponds to the component eluted from the column 130 of the GC unit 100 at each time between the steps S22 to S27, and the data processing unit 420 Further, chromatograms of the sample are generated from the plurality of mass spectra. For example, the intensity of ions of a predetermined mass-to-charge ratio (or the maximum value or the total value of the ion intensities in a predetermined mass-to-charge ratio range) on each mass spectrum is taken on the vertical axis, and time (retention time) is on the horizontal axis By taking it, a chromatogram of the sample can be generated. The generated mass spectrum and chromatogram can be displayed on the screen of the display unit 440 when the user performs a predetermined operation from the operation unit 430.

  Although the switching from the first state to the second state is performed only once in the flowchart of FIG. 4, the present invention is not limited to this, and switching between the first state and the second state may be performed a plurality of times. You may Also in this case, the sum of the duration of the first state and the sum of the duration of the second state is made equal to the execution time C of the sample analysis.

  As mentioned above, although a specific example was given and explained about a form for carrying out the present invention, the present invention is not limited to the above-mentioned example, and can be suitably changed within the range of the main point of the present invention. For example, although the MS unit 300 includes the quadrupole mass separation unit 350 in the above embodiment, the present invention is not limited to this, and the MS unit 300 includes, for example, the ion trap mass separation unit 350. A variety of things can be used, such as a thing, and a thing provided with the mass separation part 350 of time-of-flight type.

In the flowcharts of FIGS. 3 and 4, the duration A (or A ') of the first state and the duration B (or B') of the second state are determined in advance, but the present invention is not limited to this. It is not limited to For example, after the start of the first state, based on the detection signal from the detector 370 of the MS unit 300, when the analysis control unit 410 determines that the intensity of the signal derived from He ^* or the like has increased to some extent Switching to the first state (or the end of sample analysis) after the analysis control unit 410 determines that the intensity of the signal derived from He ^* or the like has decreased to some extent. Good.

  In the above embodiment, the ionization chamber 321 is grounded, and switching of the switch 325 turns on and off the application of voltage from the first bias voltage source 326 to the filament 322 to switch between the first state and the second state. Although the present invention is not limited thereto, the potential of the filament is lower than the potential of the ionization chamber in the first state, and is equal to or higher than the potential of the ionization chamber in the second state. It should just be comprised so that. Therefore, for example, in the configuration shown in FIG. 2, the switch 325 is eliminated and the bias voltage applied from the first bias voltage source 326 to the filament 322 is always constant, and the bias voltage is applied to the ionization chamber 321. A state in which the potential of the ionization chamber 321 is made higher than the potential of the filament 322 by newly providing a bias voltage source 3 and changing the value of the bias voltage applied from the third bias voltage source to the ionization chamber 321 That is, the first state may be switched between the state where the potential of the ionization chamber 321 is equal to or lower than the potential of the filament 322 (that is, the second state).

100 GC unit 110 sample vaporization chamber 120 injector 130 column 140 column oven 200 interface unit 210 sample introduction tube 300 MS unit 310 vacuum chamber 311, 312, 313 vacuum pump 320 ion source 321 Ionization chamber 321a: electron inlet 321b: electron outlet 321c: ion outlet 322: filament 323: trap electrode 324: heating current source 325: switch 326: first bias voltage source 327: second bias voltage source 328: current detection Unit 330: Extraction electrode 340: Ion transport optical system 350: Mass separation unit 351: Quadrupole mass filter 370: Detector 400: Control / processing unit 410: Analysis control unit 420: Data processing unit 430: Operation unit 440: Display Department

Claims (5)

And the pressing heat current source,
A filament that generates thermal electrons supplied with heating current from the pre-Symbol heating current source,
A sample inlet for specimen gas is introduced, and a said electron inlet thermal electrons generated in the filament is introduced, and the sample gas are respectively introduced from the sample introduction port and electronic inlet An ionization chamber that ionizes the sample gas by contacting the thermal electrons;
And ion extraction means for withdrawing the previous SL ions generated in the ionization chamber to the outside of the ionization chamber,
A mass separation unit which passes ions having a specific mass-to-charge ratio among the ions extracted from the ionization chamber by the ion extracting means, and scans the mass-to-charge ratio of the ions to be passed at a constant period; ,
A detector that detects ions of the ions that have passed through the mass separation unit;
And potential difference generating means for generating a potential difference between the front Symbol filament and the ionization chamber,
By controlling the pre Symbol potential difference generating means, a first state in which the potential of the filament was lower than the potential of the ionization chamber, the potential of the filament was increased the ionization chamber potential identical or than 2 State switching means for switching between states;
A heating current control means for controlling the heating current source to supply the heating current to the filament both before Symbol first state and said second state,
And ion extraction control means for controlling said ion extraction means to draw the ions to the outside of the ionization chamber prior Symbol first state,
State switching control means for controlling the state switching means so that the duration of the first state is longer than one execution time of the scan by the mass separation unit;
A mass spectrometer characterized by having: A filament that generates thermal electrons,
A sample inlet for specimen gas is introduced, and a said electron inlet thermal electrons generated in the filament is introduced, and the sample gas are respectively introduced from the sample introduction port and electronic inlet An ionization chamber that ionizes the sample gas by contacting the thermal electrons;
And potential difference generating means for generating a potential difference between the front Symbol filament and the ionization chamber,
By controlling the pre Symbol potential difference generating means, a first state in which the potential of the filament was lower than the potential of the ionization chamber, the potential of the filament was increased the ionization chamber potential identical or than 2 State switching means for switching between states;
While performing mass analysis on one sample, and the state switching control means for controlling the state switching means to switch between the second state and said first state,
And ion extraction means for withdrawing the previous SL ions generated in the ionization chamber to the outside of the ionization chamber,
A mass separation unit for separating on the basis of the ions extracted from the ionization chamber by a previous SL ion extraction means to the mass-to-charge ratio,
And a detector for detecting ions having passed through the mass separation portion in the front Symbol ions,
And signal the acquired in the first state a detection signal obtained by the detector during a mass analysis of previous SL one sample, signal and acquired by the second state a detection signal And a data processing unit that generates a mass spectrum of the sample using only the signal acquired in the first state.
A mass spectrometer characterized by having: The mass separation portion, be one which scans the mass-to-charge ratio of ions passing the mass fraction away portion at a fixed period,
The mass spectrometry according to claim 2, wherein the state switching control means performs switching from the second state to the first state in accordance with a predetermined timing of the cycle by the mass separation unit. apparatus. A filament that generates thermal electrons,
A sample inlet for specimen gas is introduced, and a said electron inlet thermal electrons generated in the filament is introduced, and the sample gas are respectively introduced from the sample introduction port and electronic inlet An ionization chamber that ionizes the sample gas by contacting the thermal electrons;
And potential difference generating means for generating a potential difference between the front Symbol filament and the ionization chamber,
By controlling the pre Symbol potential difference generating means, a first state in which the potential of the filament was lower than the potential of the ionization chamber, the potential of the filament was increased the ionization chamber potential identical or than 2 State switching means for switching between states;
While performing mass analysis on one sample, and the state switching control means for controlling the state switching means to perform at least once the switching to the second state from the first state,
And ion extraction means for withdrawing the previous SL ions generated in the ionization chamber to the outside of the ionization chamber,
A mass separation unit for separating on the basis of the ions extracted from the ionization chamber by a previous SL ion extraction means to the mass-to-charge ratio,
And a detector for detecting ions having passed through the mass separation portion in the front Symbol ions,
Of the obtained detection signal by the detector during a mass analysis of previous SL one sample, the sample by subtracting the signal obtained in the second state from the signal obtained in the first state A data processing unit that generates a mass spectrum;
A mass spectrometer characterized by having: The potential difference generation means applies a DC bias voltage to the filament or the ionization chamber so as to accelerate the thermoelectrons generated in the filament toward the ionization chamber.
The said state switching means switches the said 1st state and the said 2nd state by switching ON / OFF of the voltage application by this electrical potential difference generation means, The any one of the Claims 1-4 characterized by the above-mentioned. The mass spectrometer as described in.

Images