JP3333226B2 - Fourier transform mass spectrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Fourier transform mass spectrometer. More specifically, so-called process analysis such as analysis of reaction gas in a chemical plant, analysis of metabolic function and anesthesia state by analysis of living body breath and inhalation gas, or so-called medical or medical component analysis to know the progress of reaction, or For example, the present invention relates to a Fourier transform mass spectrometer suitable for analyzing so-called desorbed gas or generated gas, for example, knowing the surface state or progress of a reaction from a gas component desorbed by heating a semiconductor or a catalyst.

[0002]

2. Description of the Related Art In various chemical processes, for example, in order to maintain the optimum conditions of the process or to find the optimum conditions, samples are collected at a certain step in the chemical process. It is often necessary to analyze specific components in a sample. In various analyzes relating to such chemical processes, various analyzers or analyzers have conventionally been used. Most of them are single-function machines with limited target components, such as an ammonia meter, an oxygen meter, and a hydrocarbon meter.

On the other hand, various analyzes relating to chemical processes include the fact that, due to the nature of measurement, simultaneous analysis of multiple components is possible.
It is desired that real-time analysis be possible. In order to satisfy the above requirement for simultaneous multi-component analysis, conventional chemical analysis based on differences in the chemical properties of those components limits the target to components having similar chemical properties. Difficulties are inevitable.

[0004] Therefore, for this purpose, physical measurement (so-called instrumental analysis) for analyzing differences in physical properties that are commonly provided in any substance is a desirable means. Among such instrumental analyses, a means conventionally used as a process analyzer is a spectroscopic analyzer such as a gas chromatograph and an infrared spectrometer. However, since the gas chromatograph is based on the principle of component separation based on the retention time peculiar to the sample component, the measurement cycle requires a long time of several minutes to several tens of minutes, and it is difficult to satisfy the above-described condition of real-time measurement. It is.

In the gas chromatograph, setting of measurement conditions such as selection of a column according to a target component, designation of a temperature condition of an oven for loading the column, and setting of a flow rate of a carrier gas such as a helium gas is troublesome. There is a problem that is required. Next, the infrared spectrometer measures vibrational energy and rotational energy from infrared absorption of asymmetric molecules, and cannot detect diatomic molecule elements. For example, in the process analysis of nitrogen, oxygen, chlorine, hydrogen, and the like, the gas components to be measured cannot be measured, and the conditions for multicomponent measurement are not satisfied. Further, in the infrared spectrometer, the resolution of the spectrum is low, and it is difficult to discriminate general components such as interference between spectra of sulfur dioxide, carbon dioxide, water and the like.

The same problem remains in versatility in ultraviolet spectroscopy and other spectroscopic analyses. The mass spectrometer is based on the principle that gas molecules introduced into an analysis tube are ionized and gas components are discriminated based on the mass-to-charge ratio. Therefore, there are essentially no undetectable gas components,
For analyzing a multi-component sample, it can be said to be the most versatile analysis means. However, gas components having the same integer mass number are generally difficult to discriminate because their ions overlap.

In such a case, the conventional method is to i) detect a fragment peak of each component gas and select a peak having no overlap between component peaks (called a unipeak) to discriminate. Ii) a method of performing component discrimination from a mixed component peak group by a multiple regression method, iii)
A method in which a gas chromatograph is placed in front, and the mixed gas sample is separated into pure components, and then identified by a mass spectrometer; iv)
Using a high-resolution mass spectrometer, the mass number of the component peak was reduced to 1 /
A method of measuring with an accuracy of 1000 mass units and discriminating by elemental composition analysis.

The method i) has a problem that it lacks generality in that a peak to be selected differs depending on the component composition of the sample gas and an appropriate peak cannot always be obtained. The method ii) is based on the condition that the mass spectra of all the sample gas components are known and the pattern coefficients are correctly obtained. When an unknown component is included, there is a disadvantage that an unexpectedly large error appears when the signal-to-noise ratio of the spectrum peak is low.

The method iii) is based on the following facts:
A problem similar to the gas chromatograph described above occurs. The method iv) is based on the measurement of a so-called accurate mass number.
Know the elemental composition of the peak of interest and perform component discrimination.
Although it can be measured irrespective of the type of component, it is a method conventionally considered to be possible only with a large double focusing mass spectrometer or a large Fourier transform mass spectrometer equipped with a superconducting magnet. However, these large devices are subject to installation conditions,
Since the measurement operation is not suitable for the process site, there has been no practical application as a process analyzer.

[0010] Regarding the analysis of components in the medical field, particularly the analysis of anesthesia, in order to determine proper ventilation for a patient and to diagnose air embolism and shock during inhalation general anesthesia in an operating room, expiration by infrared absorption is necessary. A carbon gas analyzer is commonly used. In this case, since the carbon dioxide gas and laughter used as an anesthetic have the same molecular weight and similar infrared absorption, there is a problem that laughter correction is required. In some cases, a single focusing or quadrupole mass spectrometer is used, but the resolution is low and the same problems as described above remain.

In the generated gas analysis, a semiconductor surface is irradiated with a laser to analyze a desorbed gas, and there is an example of separation measurement of SiN ₂ ⁺ , SiCO ^{+ and the} like, but a large mass spectrometer is used. The prior art issues in these gas analysis fields are:
An object of the present invention is to provide a mass spectrometer which has high resolution capable of accurate mass number measurement, is compact, inexpensive, and easy to maintain and operate.

In the above-mentioned fields of use, the object to be measured is limited to a sample which is a gas at normal temperature. The Fourier transform mass spectrometer for gas analysis whose measurement target is limited as described above is realized by satisfying the following conditions. i) Since the molecular weight of a substance that is a gas at normal temperature is generally low, the measured mass range of the mass spectrometer may be set to 2 to 200 amu.

Ii) Accordingly, the ion cyclotron resonance magnetic field does not need to be high, and a permanent magnet is used. In this case, unlike a conventional Fourier transform mass spectrometer equipped with a superconducting magnet, there is no need for replenishment of liquid helium, operation and maintenance are much easier and simpler, and the device is also smaller, simpler and lower. Summed up in price.

Iii) When a permanent magnet having a magnetic field of 6,000 gauss is employed, the resonance frequency is about 4.8 MHz for hydrogen ions and about 600 KH for methane and carbon dioxide.
z to 220 KHz. Therefore, the AD converter, the memory, and the like can be sufficiently handled by a normal commercially available module. However, the permanent magnet has a large temperature coefficient, and due to the magnetic field drift, the stability of the spectrum is inevitably reduced as compared with a conventional Fourier transform mass spectrometer using a superconducting magnet.

Accordingly, an object of the present invention is to provide a Fourier transform mass spectrometer capable of performing a high-resolution mass spectrometry, in which a sufficient stability can be obtained in the above-mentioned application field, and in particular, a magnetic field drift can be automatically compensated for. To provide. Another object of the present invention is to provide a Fourier transform that can calibrate and output a measured resonance frequency according to the magnetic field drift without performing the automatic compensation on the magnetic field drift and perform high-resolution mass spectrometry. It is to provide a mass spectrometer.

[0016]

According to a first aspect of the present invention, a sample gas introduced into a high vacuum cell placed in a static magnetic field is ionized and provided in the high vacuum cell. To the irradiation electrode pair from a high-stable high-frequency source.
Cyclotron resonance frequency of ions based on certain components
By applying a high frequency having a fixed frequency close to the above, ions are excited to induce ion cyclotron resonance in ions of a specific component to be measured, and the ion cyclotron resonance is detected as a high frequency electric attenuation signal, and this high frequency electric attenuation is detected. converts the signal to a digital signal, a Fourier transform mass spectrometer to be converted to a frequency domain signal digital RF electrical damping signal which is a time domain signal, the magnetic field to form a permanent magnet or an electromagnet as the static magnetic field, the compensation magnetic field Magnetic field generating means comprising a compensation coil and a DC power supply ;
Feedback means for detecting a long-period variation of the magnetic field as a change in the ion cyclotron resonance frequency of a specific component, and returning the change as an error signal of the magnetic field variation to the DC power supply ; A Fourier transform mass spectrometer is characterized in that a magnetic field is controlled so as to be kept constant.

[0017] The object of the invention of the second means for solving the sample gas introduced into the high vacuum cell placed within a static magnetic field to ionize, high in radiation electrode pair provided on the high vacuum cell From a stable high-frequency source, based on the specific component being measured
Fixed frequency close to the cyclotron resonance frequency of the ion
High frequency and ion excited by applying a measured by inducing the ions in the ion cyclotron resonance of a specific component, the ion cyclotron resonance is detected as a high-frequency electric attenuated signal, the high frequency electric attenuated signal into a digital signal conversion, a Fourier transform mass spectrometer to be converted to a frequency domain signal digital RF electrical damping signal which is a time domain signal, the ion of a specific component and the permanent magnet or an electromagnet, a long-period variation of the magnetic field as a static magnetic field Feedback means for detecting the change as a change in the cyclotron resonance frequency and returning the change as an error signal of the magnetic field fluctuation to the high-stable high-frequency source, and adjusting the irradiation frequency so as to keep the static magnetic field / irradiation frequency ratio constant. It is a Fourier transform mass spectrometer characterized by controlling.

[0018] invention of the third means for solving the above problems, a sample gas introduced into the high vacuum cell placed within a static magnetic field to ionize, high in radiation electrode pair provided on the high vacuum cell From a stable high-frequency source, based on the specific component being measured
Fixed frequency close to the cyclotron resonance frequency of the ion
The ion is excited by applying a high frequency to induce ion cyclotron resonance in ions of a specific component to be measured, the ion cyclotron resonance is detected as a high-frequency electric attenuation signal, and the high-frequency electric attenuation signal is converted into a digital signal. In a Fourier transform mass spectrometer, which converts a digital high-frequency electrical attenuation signal, which is a time-domain signal, into a frequency-domain signal, a permanent magnet or an electromagnet as a static magnetic field, and a long-period variation of the magnetic field are converted into ions of a specific component.
A Fourier transform mass spectrometer, comprising: a calibration means for detecting a change in cyclotron resonance frequency, using a calibration coefficient calculated from the change, and calibrating the measured resonance frequency and outputting the same. .

[0019]

In the Fourier transform mass spectrometer of the present invention, a change in the ion cyclotron resonance frequency of a specific component in a sample gas is detected to compensate for a magnetic field drift or to calibrate the change in the resonance frequency. A residual atmospheric component after high vacuum evacuation, for example, nitrogen may be used. Hereinafter, this is called a reference component, and its resonance frequency is called a reference frequency.

As for the Fourier transform mass spectrometer in general, there have already been achievements by Comisarou, Marshall, etc. (Fourier transform ion cyclotron resonance mass spectrometry method and apparatus; see JP-B-59-4829). However, their equipment aims to analyze and identify unknown samples, and to excite and detect all sample ions, so that a broadband excitation magnetic field should be applied to the analysis cell and that the receiving system should have broadband characteristics. Features.

However, in the various component analyzes aimed at by the present invention, identification of an unknown sample is not included.
It is not necessary to excite all the ions of the sample gas. Therefore, a high-frequency electric field having a fixed frequency close to the cyclotron resonance frequency of the ions based on the specific component to be analyzed is applied between the pair of transmitting electrodes in the high vacuum cell. The receiving system for amplifying the high-frequency signal voltage detected by the high vacuum cell does not need to cover all gas components, and a narrow band amplifier that responds to a resonance signal corresponding to a specific ion of the sample gas can be used.

As a result, since the resonance signal of the ion which is not the object of measurement does not enter the amplification system, the limitation of the dynamic range of the high-frequency amplifier and the A / D converter is relaxed. The signal-to-noise ratio (S /
N) is improved. And other features.

The measurement is performed, for example, in the following procedure. That is, the sample gas to be measured is placed in a static magnetic field and introduced into a high-vacuum cell depressurized to a high vacuum,
It is ionized by an electron impact method or the like. Thereafter, the high-frequency transmitting means irradiates the high-frequency electric field to the ions by the high-frequency voltage applied to the irradiation electrode pair provided in the high vacuum cell, and induces ion cyclotron resonance in the ions to be measured.

[0024] The ion cyclotron resonance is detected as a high-frequency electric decay signal induced in the receiving electrode. This high-frequency electric attenuation signal is amplified and converted into a digital signal by a high-speed A / D converter. The high-frequency electric attenuation signal is stored as a time-domain signal. After the measurement period, the time domain signal is converted into a frequency domain signal by a Fourier transform technique. This frequency domain signal corresponds to a mass spectrum. Since the frequency and the mass number have a relationship represented by the following equation (2), unit conversion can be easily performed, and a normal mass spectrum can be obtained. can get.

As described above, in the present invention, the irradiation frequency approximating the ion cyclotron resonance frequency of the specific target ion to be measured is applied to the irradiation electrode pair, so that the detected high-frequency attenuation signal is digitally converted. Within the limited dynamic range, the specific target ions can be excited sufficiently large to be measurable. In the Fourier transform mass spectrometer, the specific target ions in the sample gas can be continuously detected by continuously or periodically supplying the sample gas to the high vacuum cell.

By the way, in the Fourier transform mass spectrometer, when a permanent magnet or an electromagnet is used as a static magnetic field,
When such a Fourier transform mass spectrometer is operated for a long time, it is inevitable that the static magnetic field gradually changes due to a temperature change or the like. In a long-term analysis, when the change in the static magnetic field or the like becomes substantially 10 ⁻³ or more, the irradiation efficiency for ions decreases, and it becomes difficult to accurately detect specific ions.

Therefore, in the present invention, the change of the static magnetic field / high frequency ratio caused by the drift of the static magnetic field over time is compensated by the first and second means of the present invention, or by the third means of the present invention. Any of the first to third aspects of the present invention, such as calibrating the ion cyclotron frequency, enables accurate mass spectrometry.

More specifically, in the first means of the present invention, the change in the static magnetic field is detected as the ion cyclotron frequency of the reference component, that is, the change in the reference frequency.
This change is fed back to the DC power supply as an error signal of the magnetic field fluctuation. The DC power supply controls a current flowing through the magnetic field compensation coil so as to eliminate the change in the static magnetic field based on the returned error signal, and stabilizes the static magnetic field. That is, the first means is a means for stabilizing the static magnetic field by using a highly stable transmitter as an irradiation frequency for the reference component and using the frequency as a control standard.

Further, in the second means of the present invention, the change in the static magnetic field is detected as the ion cyclotron resonance frequency of the reference component, that is, the change in the reference frequency, and this is returned to the high-stable high-frequency source as an error signal of the magnetic field fluctuation. I do. The high-stable high-frequency source controls the output of the high-stable high-frequency source, that is, the irradiation frequency, based on the returned error signal, so that the static magnetic field / irradiation frequency ratio is kept constant. In other words, the second means is that the static magnetic field becomes the standard for control, and the output frequency of the high-stability high-frequency source is changed to follow the static magnetic field.
This is a means for keeping the irradiation frequency ratio constant.

In the third means of the present invention, upon measurement, the resonance frequency of the reference component, that is, the reference frequency is measured and stored. If the ion cyclotron resonance frequency changes with a change in the static magnetic field, a calibration coefficient of the ion cyclotron resonance frequency measured based on the stored reference frequency is calculated. Then, the measurement frequency of the ion cyclotron resonance is calibrated using the calibration coefficient. In the third means, the drift of the static magnetic field is not particularly controlled.
The measured resonance frequency is calibrated based on the ion cyclotron resonance frequency actually measured from the relationship with the variation of the irradiation frequency ratio.

As described above, in the present invention, even if there is a temporal change in the static magnetic field, the temporal change is detected as a change in the ion cyclotron resonance frequency, and according to the change in the ion cyclotron resonance frequency, Alternatively, control the irradiation frequency or static magnetic field to compensate for changes in the magnetic field over time, or to calibrate the frequency measurement value and to withstand changes in the ambient temperature surrounding the room or equipment where the Fourier transform mass spectrometer is installed. Enables measurement of accuracy.

[0032]

Embodiments of the present invention will be described below in detail. FIG. 1 is an overall circuit block diagram showing one embodiment of the first means of the present invention. As shown in FIG. 1, the Fourier transform mass spectrometer 1 includes a high vacuum cell 2, a magnetic field generating means including a permanent magnet 3, a magnetic field compensation coil 3c, and a DC power supply 12 for supplying a compensation current to the magnetic field compensation coil (see FIG. 1). 5), a high-frequency transmitting means 4, a control circuit 6 for controlling a high-frequency pulse sequence related to ion cyclotron resonance and controlling an electron flow for ionizing a sample gas under the control of a computer 27, It has a signal detecting means 7, an arithmetic control means 8, a keyboard 9 and a CRT display 10.

The high vacuum cell 2 includes an ultra-vacuum chamber 11
And is housed in a thermostat (not shown). As the high vacuum cell 2, a cubic cell including a pair of electrodes orthogonal to the magnetic field direction of the permanent magnet 3, a pair of irradiation electrodes parallel to the magnetic field and orthogonal to each other, and a pair of receiving electrodes can be used. . Such cubic cells include MBComisarow; "Cubic Tra
pped IonCell for Ion Cyclotron Resonance "Int.J.
Usual cells described in Mass Spect. Ion Phys., 37, (1981) pp. 251 to 257 can be used.

In this cubic cell, as shown in FIG. 2, a pair of electrodes P and P ′ arranged perpendicular to the direction of the magnetic field cause the drift of ions in the high vacuum cell 2 in the magnetic axis direction. In order to prevent this, a slight positive potential, for example, a positive potential of 0.1 to 2 V is applied. The irradiation electrodes T and T 'are disposed between the pair of electrodes P and P' so as to face each other along the direction of the magnetic field, and a high-frequency signal for exciting cyclotron resonance to ions generated in the cubic cell is short-lived. For example, 0.1-10ms
For a period of time. Receiving electrode R, R '
Are arranged so as to face each other along the direction of the magnetic field, and to be orthogonal to the electrodes P, P ′ and the irradiation electrodes T, T ′, so as to receive a high-frequency signal voltage induced by resonance. I have. In FIG. 2, 2a is a grid, and 2b is a filament.

The constant temperature bath operates so as to keep the temperature change of the magnetic field generating means within approximately 1 ° C. with respect to the change of the ambient temperature, thereby limiting the magnetic field compensation range and appropriately controlling the change of the compensation current. It is an additional device to keep in the range.

The permanent magnet 3 includes a pair of magnetic pole pieces 3a and 3b disposed opposite to each other with the high vacuum cell 2 interposed therebetween.

The use of the permanent magnet 3 is one of the features of the present invention. When a superconducting magnet is used, its magnetic field stability is extremely high, and the mass / spectrum obtained does not undergo temperature change or aging. However, in the case of a permanent magnet or an electromagnet, the magnetic field changes under the influence of the ambient temperature, and its temperature coefficient is about-
2 × 10 ^-4 / ° C, about -5 × 10 ^-4 to -6 for rare earth magnets
× 10 ^-3 / ° C. Therefore, in order to guarantee a resolution of 10 ⁴ to 10 ⁵ , it is necessary to compensate for a magnetic field variation due to temperature or the like.

Therefore, when the permanent magnet 3 is used as in this embodiment, first, the compensation by the magnetic shunt steel is preferably adopted as a means for compensating the temperature coefficient. This compensation can improve the temperature coefficient several times. For example, the temperature coefficient of neodymium, iron, and boron-based bonded magnets (Nd ₂ Fe ₁₄ B) is currently 1 × 10 ⁻³ / ° C.

Based on the high-resolution characteristics of the Fourier transform mass spectrometer 1, the elementary analysis of the sample gas by precise measurement of 1/1000 mass unit, that is, so-called millimass measurement, requires an order of magnitude improvement in stability. It is necessary to. The high-frequency transmitting means 4 has a high-frequency transmitter 4a and a high-frequency transmitter 4b. As shown in FIG. 3, the high-frequency oscillator 4a includes a high-frequency source 4c for compensation and a high-frequency source 4 for measurement.
d and a frequency synthesizer 4e.

The compensating high frequency source 4c supplies the cyclotron resonance frequency of the reference component ion. High frequency transmitter 4
The frequency a is selected equal to the resonance frequency of the component to be analyzed. The high-frequency transmitter 4b receives the output of the frequency synthesizer 4e, and pulse-modulates the output thereof according to a command from a computer via the control circuit 6 to excite the transmission electrodes T and T 'of the high vacuum cell 2. Provides a two-phase high frequency pulse of power.

The control circuit 6 operates such that various operations such as ionization, high-frequency irradiation, measurement, elimination of residual ions, and the like specified in the Fourier transform method are performed in a predetermined order.
The high-frequency transmission means 4 and the emission controller 6 are commanded under computer management. An example of the operation sequence is shown in FIG. 4 together with the control voltage of each electrode of the high vacuum cell and its time change.

FIG. 4 shows an example of a typical relationship between the voltage applied to each electrode of the analysis cell and the induced signal in the analysis cycle. (A) First, the filament potential is -20 to -70 (V)
The sample gas molecules are ionized by the electron beam irradiated into the cell. (B) After a predetermined time after the electron beam irradiation, the output gate of the high-frequency transmitter is opened, and (c) the irradiation frequency, which is a high-frequency pulse, is applied to the transmission electrode of the high vacuum cell from the high-frequency transmitter.

(D) The ions excited by the irradiation frequency induce ion cyclotron resonance. After the ions are excited, the output gate is closed. (E) In this way, an ion cyclotron resonance signal is induced at the receiving electrode. (F) After the resonance signal measurement, positive and negative potentials are respectively applied to the pair of trap electrodes placed orthogonal to the magnetic axis just before the next measurement cycle, and ions remaining in the cell are erased.

The control circuit 6 receives a command from the programmable sequencer 5 and irradiates the sample molecules introduced into the analysis cell with an electron beam to irradiate and ionize the sample molecules prior to the application of the high-frequency pulse. This circuit controls the voltage of each electrode in the analysis cell and the potential of the filament for thermionic emission for performing a function of cutting off the electron beam irradiation during a signal measurement period and a function of erasing residual ions at the end of the measurement.

The detecting means 7 includes a preamplifier 20, a high-frequency amplifier 21, a low-pass filter 22, and an A / D converter 23 for performing high-speed processing. The preamplifier 2
Numeral 0 designates a compensation signal amplifier 24, a measurement signal amplifier 25, and a frequency synthesizer 26 as shown in FIG. 3, and adjusts the ion cyclotron resonance frequency induced by the receiving electrodes R and R 'in the high vacuum cell 2. After individually performing narrow-band amplification, they are combined and output to the high-frequency amplifier 21.

The high-frequency amplifier 21 includes a frequency mixer (not shown). That is, mixing processing of the narrow-band amplified ion cyclotron resonance frequency and a reference signal of a frequency f _o separately input from the arithmetic and control unit 8 is performed, and the resonance high-frequency signal is converted to a low-frequency signal having a difference frequency between the signal frequency and f _o. And converts the low-frequency signal to a low-pass filter 2
2.

This frequency conversion holds the amplification information of the signal wave and converts only the frequency to a difference frequency from the reference frequency in the same manner as the so-called heterodyne detection in communication equipment. Preferably, the reference frequency f ₀ is set higher than the ion cyclotron resonance frequency. Low pass filter 22
Is a signal excluding a return signal at the time of A / D conversion in the A / D converter 23.
3 is set within 1/2 of the clock frequency.

The A / D converter 23 converts the resonance signal from which unnecessary frequency bands have been removed and amplified to a signal level at which A / D conversion is possible, into a digital signal, and outputs the digital signal to the arithmetic and control means 8. It is supposed to. The arithmetic control means 8 controls a computer 27 for performing overall control, a storage device 28, an output device 29, and the A / D converter 23, and takes in the output of the A / D converter 23 at a high speed. And an interface 30 for transmitting a control signal from a computer 27 to the control circuit 6 and the DC current 12.

Thus, the unnecessary frequency band is removed, and the A / D
The resonance signal amplified to a signal level suitable for the converter 23 is converted into a digital signal by the A / D converter 23, transferred to the computer 27 via the interface 30, and stored in the storage device 28 as time domain data. Is done. After the measurement, the time domain data is subjected to a fast Fourier transform process by the computer 27, and is converted into frequency domain data, that is, a normal mass spectrum.

Of course, all of these measurement control operations are automatically executed by control signals from the computer 27 via the interface 30. First, a molecular peak ion or a base peak ion is selected for a component to be measured. Assuming that each of the resonance frequencies is ω ₀ and the applied static magnetic field is B, an intermediate ω of Expression (2)
_o = Be / m. Here, m is the mass number of the target ion, and e is the charge.

Therefore, if the irradiation frequency applied to the transmitting electrode is made substantially equal to ω _o , ion cyclotron resonance is continuously observed. But the static magnetic field drifts,
If B changes, the relationship of equation (2) breaks down, making spectrum measurement difficult. In the first means, passing a compensation current from the DC power supply 12 to the magnetic field compensation coil 3c, the compensation magnetic field .DELTA.B, in addition to the magnetic field B _o produced by the permanent magnet, an equation (3) B = B _o
+ ΔB.

Now, if B changes due to the drift of the permanent magnet magnetic field B _o , the resonance frequency ω _o also changes, and the difference from the irradiation frequency is detected. In the first means, this frequency difference is used as an error signal of the magnetic field change as a DC power supply 12
And ΔB is controlled so that B is kept constant. Thereby, regardless of the drift of the permanent magnet magnetic field _Bo ,
Stable measurement over a long period of time becomes possible.

Next, the second means will be described. FIG. 6 is a block diagram showing one embodiment of the present means. In the second means, the error voltage is not a magnetic field but is fed back with respect to the frequency, so that the control command of the computer is given to the high-frequency oscillator 4a. The high-frequency transmitter 4a is a transmitter having a so-called programmable function that can change a transmission frequency, an output voltage, and a phase according to a command from a computer. Specifically, a frequency synthesizer, a function generator, a voltage frequency converter, and the like can be used.

[0054] at the start of measurement, the formula for the reference frequency omega _o which are represented by (2) the magnetic field B changes to B'n, if became omega _o ', the rate of change k of the magnetic field equation (4) As k =
B '/ B. Therefore, the compensation high-frequency source 4
By controlling the output frequency of c (FIG. 3) to be kω _o , the resonance condition of the reference component is maintained. Similarly, the frequency of the measuring high-frequency source 4d is controlled to k times.

[0055] Upon initially measured and stored as a reference value the resonance frequency ω _o of the reference component. Also, the measurement frequency ω _i
Is stored in the same manner. Resonance frequency omega _o is measured in the subsequent continuous or constant time interval 'change rate by k = omega _o'
/ Seek omega _o, compensating the high-frequency source, measurement of high-frequency sources, respectively frequency omega _o, against omega _i, kW _o, is controlled to be kW _i. Thus, stable measurement can be performed for a long time despite the fluctuation of the static magnetic field B.

Next, the third means will be described. FIG.
FIG. 4 is a block diagram showing an embodiment of the present means. In the third means, since the error voltage is not fed back to the magnetic field or the frequency, the control command of the computer is not given to the DC power source or the high-frequency transmitter 4a. Also,
The high-frequency transmitter 4a sends out the output of the compensating high-frequency source 4c in addition to the measurement high-frequency source 4d (see FIG. 3). The frequency is set equal to the resonance frequency of the peak of each of the component to be measured and the reference component. For example, in the case of nitrogen, this frequency is about 345 K at a magnetic field of 0.6 Tesla.
Hz.

The outputs from the measuring high-frequency sources 4c and 4d are:
The combined signals are subjected to pulse modulation and power amplification in the high-frequency transmitter 4b and applied to the transmission electrodes T and T 'of the high vacuum cell 2. The compensation signal and the measurement signal induced in the receiving electrodes R and R ′ are combined in the preamplifier 20 through narrow-band amplification, and transferred to the high-frequency amplifier 21. Both signals are converted to a low frequency signal having a frequency difference from the high stability reference signal by a frequency synthesizer 26 included in the high frequency amplifier 21.

In this frequency conversion, only the frequency is converted to a difference frequency from the reference signal frequency while holding the amplification information of the signal wave by a method similar to the so-called heterodyne detection in communication equipment. The reference frequency f ₀ is set higher than the normal signal frequency. FIG. 8 shows this frequency relationship. In FIG. 8A, the resonance frequency of the reference component ion 1 is fr ₁ , the resonance frequency of the measurement component ion 2 is fr ₂ ,
The frequency of the reference signal is displayed as f _0.

The resonance angular frequency ω _c is given by ω _c = eB / m in the equation (2) as in the first means.

That is, the resonance frequency is proportional to the static magnetic field,
It is inversely proportional to the mass number. If the measurement component is, for example, O ₂ with respect to the reference component N ₂ , the respective resonance frequencies fr ₁ ,
The relationship of fr ₂ can be represented as shown in FIG. Note that the resonance frequency fr ₁ is selected to be a value somewhat higher than fr ₂ . A signal having a frequency difference from the frequency of the reference signal through the frequency synthesizer 26 has a frequency f ₀ as a base point of the frequency, a reference frequency f ₀ and a resonance frequency fr, as shown in the lower part of FIG. Difference frequency f from ₁
a _1, the difference between the reference frequency f ₀ and the resonant frequency fr ₂ frequency fa ₂
Becomes a low frequency. Here, a fa ₁ <fa ₂ is displayed in the order of mass number of the ion.

Now, the static magnetic field B
Drifts to kB, fr ₁ and fr ₂ become kfr ₁ and kfr ₂ respectively. Here, the coefficient k is a degree of the temperature coefficient of the magnet, and can be manufactured by a conventional technique when k <10 ^-3 to 10 ^-4 . This state is shown in FIG.
(B) in FIG.

The reference signal frequency and the measurement signal frequency both drift, so that the spacing between the two frequencies also changes. At the start of the measurement, fr ₁ is measured and stored in a computer.
The resonance frequency fr ₁ ′ of the reference component at that time is measured, and k
= Fr ₁ / fr ₁ ′ {Equation (5)}. At this time, the spectrum is displayed by drift fa ₁ '.

Therefore, the frequency fa ₁ to be displayed as a spectrum is expressed by the following equation (6): fa ₁ = ｛f ₀ − (f
₀ −fa ₁ ′)｝ / k makes it possible to obtain a drift-compensated resonance frequency. Similarly, the resonance of the measured component is k
Although fr ₂ and are drifted and mixed with f _0, its frequency is converted to _{fa 2 '= f 0 -kfr 2} . Therefore, as equation (7), fa ₂ = f _o − (f _o −fa ₂ ′)
· (F _o -fa ₁₎ / with (f _o -fa ₁ '), a drift compensated resonance frequency is obtained.

As described above, according to the present embodiment, even in the Fourier transform mass spectrometer 1 using the permanent magnet 3 which is inferior in stability to the superconducting magnet, the stability in the sample gas is sufficient for practical analysis. The change in the concentration of the analysis target component can also be known. Note that the computer 27 transmits the transferred A
The Fourier transform is performed on the D-converted resonance signal, and the resonance frequency of the reference component ion is calculated and stored in the storage device 28.

FIG. 9 shows a procedure for calculating a compensation value in the above embodiment of the third invention. The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the gist. For example, when there are a plurality of components to be analyzed, a corresponding high-frequency source for measurement and a narrow-band measurement signal amplifier may be added. This can be easily implemented in a plug-in unit type or the like.

For example, instead of plugging in the high frequency source unit for each target component, a single frequency synthesizer may be provided, and the irradiation frequency may be sequentially switched during the ion excitation period. In this case, the irradiation time for each ion is reduced by the number of measurement components, but if the high-frequency output is correspondingly increased, the same irradiation efficiency can be obtained.

Alternatively, using a device such as a commercially available arbitrary waveform generator, a composite waveform of waveforms of a required number of frequencies is stored in a storage device in advance, and is read out at an appropriate cycle. It can also be transmitted to a high frequency transmitter. In this specification, the static magnetic field is mainly described as a permanent magnet, but it is needless to say that the same effect can be expected by using an electromagnet. In particular, in the case of an electromagnet, an excitation power supply is provided. Therefore, in the first means, the error signal is directly negatively fed back to the excitation power supply without using the DC power supply 12 for magnetic field compensation to stabilize the static magnetic field. Can be.

[0068]

According to the operation of the present invention described above in detail, the fluctuation of the magnetic field of the permanent magnet used in the Fourier transform mass spectrometer is compensated, and the separation between sample components having the same integral mass number is measured by measuring the precise mass number. Measurement becomes possible. As a result, the following effects can be obtained. (1) In the process analysis, the component separation of the mixed gas sample becomes practically possible in real time.

As a result, it is possible to perform component separation which requires a long time in real time by relying on a process gas chromatograph. Further, unlike the method using a combination of various types of single-purpose measuring instruments, any gas component introduced from the plant can be analyzed without being limited by the target component.

The device can provide almost the only analytical method that meets the essential demands of the process analysis of multi-component real-time measurement.

(2) In the breath analysis, nitrogen and carbon monoxide, nitrous oxide and carbon dioxide, etc.
Separate measurements of vital components of breath and inspiration of the living body can be performed in real time. In particular, the ability to separate nitrous oxide and carbon dioxide makes it possible to determine proper ventilation, diagnose air embolism, diagnose shock, etc. in real time as a monitor during general anesthesia by inhalation.

(3) Also in the analysis of generated gas, element analysis of ions, which has conventionally relied on a large-sized mass spectrometer, can be performed in a short time with a small device. (4) Short-lived components such as nitrogen oxides can be analyzed at the time of generation.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an apparatus according to an embodiment of the first means of the present invention.

FIG. 2 is an explanatory view showing a high vacuum cell of the apparatus.

FIG. 3 is a block diagram showing a high-frequency source and a detecting means of the apparatus.

FIG. 4 is a timing chart showing changes in electrode potentials of the high vacuum cell.

FIG. 5 is a block diagram showing a main part of an apparatus according to an embodiment of the first means of the present invention.

FIG. 6 is a block diagram showing a main part of an apparatus according to an embodiment of the second means of the present invention.

FIG. 7 is a block diagram showing an apparatus according to an embodiment of the third means of the present invention.

FIG. 8 is an explanatory diagram showing a relationship between resonance frequencies of ions and a frequency change due to a magnetic field drift.

FIG. 9 is a flow chart of a program showing a procedure for calculating a compensation value in an embodiment of the third means of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fourier-transform mass spectrometer 2 High vacuum cell 3 Permanent magnet 4 High frequency source 7 Detection means 8 Arithmetic control means

Continuation of the front page (56) References JP-A-51-91791 (JP, A) JP-B-55-34380 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01J 49 / 26-49/42 G01N 27/62

Claims (3)

(57) [Claims] 1. Introduction into a high vacuum cell placed in a static magnetic field
The sample gas is ionized and the illumination provided in the high vacuum cell
To the electrode pairOf ions based on the specific component being measured
A fixed frequency close to the cyclotron resonance frequencyHigh frequency
By applying a high frequency electric field to the ions,
Ion cyclotron for specific component ions to be determined
Induces resonance and increases the frequency of the ion cyclotron resonance.
Detected as a high-frequency electrical attenuation signal
Is converted to a digital signal, and the time domain signal digital
Fourier to convert high frequency electrical attenuation signal to frequency domain signal
Conversion mass spectrometerAnd,  Permanent magnet or electromagnet as static magnetic field and static magnetic field fluctuation
A variable magnetic field compensating coil for compensating forDC power supplyConsists of
Magnetic field generating means and ions of a specific component
・ Detection as a change in cyclotron resonance frequency
The variation is used as an error signal of the magnetic field fluctuation,DC power supplyReturn to
Return means to return the static magnetic field / irradiation frequency ratio constant
Characterized by controlling the magnetic field to maintain
Lie transform mass spectrometer. 2. A sample gas introduced into a high-vacuum cell placed in a static magnetic field is ionized, and a specific electrode to be measured is applied from a highly stable high-frequency source to an irradiation electrode pair provided in the high-vacuum cell.
Of the ion close to the cyclotron resonance frequency
A high frequency electric field is applied to the ions by applying a high frequency of a constant frequency to induce ion cyclotron resonance in ions of a specific component to be measured, and the ion cyclotron resonance is detected as a high frequency electric decay signal. the attenuated signal is converted into a digital signal, a Fourier transform mass spectrometer to be converted to a frequency domain signal digital RF electrical damping signal which is a time domain signal, and the permanent magnets or electromagnets as a static magnetic field, the long period of the magnetic field variation Is detected as a change in the ion cyclotron resonance frequency of the specific component, and the change is provided as an error signal of the magnetic field fluctuation, and feedback means is provided for feeding back to the high-stable high-frequency source .
An Fourier-transform mass spectrometer, wherein an irradiation frequency is controlled so as to keep a static magnetic field / irradiation frequency ratio constant. 3. A sample gas introduced into a high vacuum cell placed in a static magnetic field is ionized, and an ion electrode based on a specific component to be measured is applied to an irradiation electrode pair provided in the high vacuum cell .
By applying a high-frequency electric field having a fixed frequency close to the cyclotron resonance frequency, a high-frequency electric field is applied to the ions to induce ion cyclotron resonance in ions of a specific component to be measured, and the ion cyclotron resonance is detected as a high-frequency electric attenuation signal. and converts the high-frequency electric attenuated signal to a digital signal, a Fourier transform mass spectrometer to be converted to a frequency domain signal digital RF electrical damping signal which is a time domain signal, and the permanent magnets or electromagnets as a static magnetic field, Calibration means for detecting a long-period variation of the magnetic field as a change in the ion cyclotron resonance frequency of a specific component, and calibrating and outputting the measured resonance frequency using a calibration coefficient calculated from the change. A Fourier transform mass spectrometer characterized by the above-mentioned.