JPS5815733B2 - sekisouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mass spectrometer used for exhaled gas analysis and the like.

A mass spectrometer introduces a sample gas into an ion source, ionizes it, extracts the ion flow, deflects it using a magnetic field or a magnetic field and an electric field, and selectively detects it according to the mass-to-charge ratio (m/e). This is to analyze the composition.

Conventionally, in this type of mass spectrometer, the total pressure of the sample gas (partial pressure of each component) is affected by the exhaust characteristics of the gas introduction system, especially the viscous flow characteristics, and the generation and disappearance of water vapor during the gas introduction process. (sum) changes, and nonlinearity appears in the detected ion beak partial pressure.

For this reason, measures have been taken such as calibrating the introduction system taking into account the viscosity of the system and keeping the water vapor partial pressure constant using a three-stage exhaust method, but these measures have resulted in significant losses and have not resulted in sufficient measurement accuracy. The disadvantage was that it could not be done.

This invention has been made in view of the above points, and provides a mass spectrometer that improves measurement accuracy by performing simple and unified processing for correction factors such as the influence of gas viscosity. It is something.

This invention is based on the following experimental facts: (1) the composition ratio before and after gas introduction does not change with respect to fluctuations in ion flow due to changes in the viscosity of the sample gas; (2) the gas introduction system Even if the exhaust characteristics change, the gas composition ratio hardly changes (3
) Contamination of impurity gas such as water vapor during the gas introduction process,
It was derived based on the fact that even if there is extinction, the component ratio of the introduced sample gas does not change.

That is, the mass spectrometer according to the present invention introduces a sample gas into an ion source, ionizes it, and extracts it, separates and detects ion beams from the ion flow according to the mass-to-charge ratio, and detects all detected ions. It is characterized in that the partial pressure ratio of each component gas is determined by calculating the sum of the peak values and dividing the individual ion peak values by the sum.

The present invention will be described in detail below with reference to the drawings.

Figure 1 shows the configuration of the ion source that ionizes the sample gas and the part that deflects and focuses the ion flow extracted from the ion source, and Figure 2 shows the detection processing system for the detected ion flow signal. There is.

That is, reference numeral 1 denotes, for example, an electron impact type ion source, in which sample gas introduced therein is ionized by an electron beam controlled by an electron current control circuit 2.

The ionized and extracted ion stream 3 enters the deflection magnetic field 6 from the ion acceleration scanning circuit 4 through the acceleration slit 5 to which an acceleration scanning voltage is applied.

In this deflection magnetic field 6, the ion stream 6 is deflected according to the m/e of its constituent components, and among the deflected ion streams, the ion stream corresponding to a desired m/e is detected by the ion collector I. .

The ion flow signal detected by the ion collector 7 is input to the separation circuit 9 via the ion contraction amplification circuit 8.

A synchronizing signal is sent to the separation circuit 9 from the ion acceleration scanning circuit 4. In other words, by scanning the acceleration voltage of the ion stream 3 extracted from the ion source 1, the degree of deflection in the magnetic field 6 is sequentially determined. The fixed ion collector 7 detects ion current signals with different m/e obtained by scanning and deflecting the ions, and the detected ion current signals are converted into m/e by a separation circuit 9 synchronized with the ion acceleration scan. It separates and extracts the signal corresponding to the signal and sends it to the next signal processing system.

The ion flow signal PHG1.corresponds to the number n of target ions separated by the separation circuit 9. PHG2・・・・・・
PHG n sequentially enters the amplifier circuits 101.10□...10n, as shown in FIG.

The output of the amplifier circuit 101.10□...10n is connected to the fragment correction input terminal 111. , 11□・・・・・・1
1n gain adjustment amplifier circuits 121, 122...
...Enter 12n.

For example, if the fragment ion of PH01 matches PH02, PH0 is input to the fragment correction input terminal 11.
Make sure to enter 2.

That is, to give a specific example, when analyzing CO□ and N2, CO2 is rn/e −”44 and m/e =
28 d, and N2 is m/e = 28 and m/e = 1
4, a relatively large ion beak appears.

Therefore, in a low-resolution device, CO and N separated from CO2 are
The second ion beak cannot be separated and overlaps.

Therefore, in order to find the accurate N2 m/e = 28 I1-beak value, m/e = 28 resulting from CO□
The ratio of the peak value of m/e244 to the peak value of m/e244 is determined in advance, and the peak value of m/e28 is determined from the peak value of m/e244, and that value is calculated from the peak value of m/e244. Subtract from the peak value of 28.

Such fragment correction is performed by the gain adjustment amplifier circuit 12.
By performing this at 0.12□...12n, accurate peak values of each ion flow are determined.

In this way, the amplifier circuit 12. , 12□・・・・・・1
The accurate ion peak values obtained from 2n are respectively taken as the dividend number X of the dividers 13□, 132...13n, and on the other hand, each ion peak value is added to the sum through the adder 14. This is each divider 13,, 132...
...The divisor of 13n is manpower Y.

As a result, the outputs of the dividers 130, 132, .

1jPQ2...Pon will be obtained.

On the other hand, a reference gas of known pressure is introduced into the ion source 1 together with the sample gas to be analyzed, and the ion flow signal P of the reference gas is
Hs is passed through the amplifier circuit 10s and switched to the output of the adder 14 to each divider 13□.

13□・・・・・・13n divisor input, the ratio of each ion to the reference gas pressure can be found. By multiplying these ratios by the reference gas pressure, the exact fraction of each ion in the sample gas can be calculated. pressure can be determined.

In the mass spectrometer described above, first, the influence of nonlinearity due to the viscous flow characteristics of the sample gas introduction system is removed.

For example, in the analysis of a CO2-02 gas mixture, when calibrating with a straight line without considering viscosity, according to experiments,
If CO□ is measured to be 44%, the true value at this time is 56% when viscosity is taken into account.

The error in this case is about 20%, but according to the above embodiment, the error is about a factor of ±1.

Even in the case of other gas mixtures, according to the present invention, the error in principle is very small; for example, in the CO□-〇□-N2 system, ±
1.5%, and in the 0□-N2-A system, it is about ±1 factor.

In addition, according to this invention, the influence of fluctuations during the introduction process of gases such as water vapor that are not to be measured is removed, and even if the emission current or the amount of introduced gas changes, it can be corrected within the accuracy of the divider. Furthermore, if the calibration is simple and the electric circuit is stable, there is no need to calibrate each measurement using a reference gas, and various other effects can be obtained.

Note that this invention is not limited to the above embodiments,
Various modifications can be made.

For example, in the embodiment, as many dividers as there are ions to be measured are provided, but inputs may be sequentially switched using one divider.

Further, a gain adjustment circuit controlled by the adder 14 may be used instead of the dividers 131, 132, . . . , 13n.

That is, by passing each ion flow signal output through a gain adjustment circuit that is inversely proportional to the output of the adder, the partial pressure ratio of each ion can be determined in the same manner as in the embodiment.

However, this case is limited to cases where the total pressure does not change even if the composition of the sample gas changes.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an ion source and a portion that deflects and detects an extracted ion flow in an example of a mass spectrometer according to the present invention, and FIG. 2 is a diagram showing a detection processing system for detected ion flow signals. FIG. 1... Electron impact ion source, 2... Electronic current control circuit, 3... Ion flow, 4...
...Ion acceleration scanning circuit, 6...Magnetic field, 7...
... Ion collector, 8 ... Ion current amplification circuit, 9 ... Separation circuit, 101゜10□ ...
...10n110s...amplifier circuit, 111
゜11□...Iln...Fragment correction input terminal, 120.122...12n...
...Amplification circuit, 13□. 13□・・・13n・・・Divider, 14・
...Adder.

Claims (1)

[Claims] 1. An ion source that ionizes and extracts sample gas, a means for separating and detecting ion peaks from the ion flow extracted from this ion source according to the mass-to-charge ratio, and a method for detecting all ion peak values detected by this means. A mass spectrometer comprising means for calculating a sum and dividing individual ion peak values by the sum.