JPH02163651A - Gas chromatograph mass spectrographic apparatus - Google Patents

Abstract

PURPOSE:To obtain analysis results with good accuracy by calculating the intensity ratios of detection signals which are respectively detected with channel selection by a detector and comparing the ratios with a preset threshold value. CONSTITUTION:The intensity ratios of the detection signals which are respectively detected with the channel selection by the detector 12 are calculated. A comparison discrimination section 48 compares the intensity ratios with the preset threshold value and discriminates the differences thereof. The discrimination results are applied to a level control section 50. The level control section 50 outputs the correction signal to maintain the detection signals at a base line only when the intensity ratios are below the threshold value in accordance with the discrimination results. The correction signal is not outputted if the intensity ratio are above the threshold value. The ghost peak occurring in the reaction of gaseous O2 and hydrocarbon does no longer appear on the mass fragmentgrams to be measured in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial application field The present invention is applicable to gas chromatograph mass spectrometry
S), especially O, impurity gas in the gas (H2C
, GO, CO, etc.).

(b) Prior art Generally, O gas contains impurity gases such as H20 and COSC02. When such impurity gases are analyzed using a gas chromatograph mass spectrometer, when measuring l·-tal ions (gas chromatogram) without mass separation, the result is 0. Since the retention times of the and CO ions are relatively similar, as shown in FIG. 3(a), the co ion peak becomes unrecognizable due to the peak of the O7 ion, which is present in large quantities. Therefore, qualitative and quantitative analysis cannot be performed.

In such a case, the conventional technology uses so-called mass fragmentography (hereinafter referred to as MF), which selectively detects only ions having a preset specific mass number by switching the accelerating voltage applied to the mass separation section at high speed. method is adopted. According to this MP, for example, by setting m/z (m is mass number, 2 is electric charge) to "28" and "44" and switching each channel alternately in time division, m/z CO ion at z=28, m/z=44
It is possible to separate and detect each CO7 ion.

(c) Problems to be Solved by the Invention However, even when the MP method is adopted, the following problem occurs when a large amount of O gas is present.

In other words, the inner walls and spaces of the mass spectrometer housing are contaminated with hydrocarbons (C) due to contamination or backflow of oil from the vacuum pump.
nHm) is present, so that if a large amount of O, gas is introduced into the housing, this 0. The gas and hydrocarbon undergo the following reaction.

Ot+CnHm-4CO+ CO2+ H3O+ Cn
tHmt+- Therefore, the measured mass fragment graffiti, as shown in Figure 3(b) and (C), is 0.
．． A so-called ghost peak P of CQ and CO7 appears at a location corresponding to the retention time of .

When such a ghost peak appears, it can be compared to the true C
It may be mistakenly recognized as a peak of O or CO2 ions, and peak separation may become insufficient, resulting in poor quantitative calculation accuracy, making it impossible to obtain accurate analytical results.

The present invention has been made in view of the above circumstances, and when analyzing impurity gases such as H2O and CO1CO7 in 02 gas by MP, the measured mass fragmentogram shows that O, gas-induced The purpose is to prevent ghost beaks from appearing and obtain highly accurate analysis results.

(d) Means for Solving the Problem 0. Since the retention time during which impurity gases such as 820, co, and COz in the gas are separated by a gas chromatograph is different from each other, in principle, in each mass fragmentogram to be measured, These peaks never appear at the same time. However, if the peaks appear at the same timing, this would mean 0. It can be considered as a ghost peak resulting from the reaction between gas and hydrocarbon. When the peaks appear at the same timing in this way, the ratio of both detection signals is constant. On the other hand, when the peaks appear at different timings, the ratio of both detection signals becomes large. Therefore, by comparing the ratio of both detection signals with a preset threshold, it is possible to determine whether it is a goose peak or not.

The present invention focuses on this point, and in order to achieve the above object, it includes a switching signal generating section that generates a channel switching signal, and ions having a corresponding mass number in synchronization with the channel switching signal. A gas chromatograph mass spectrometer equipped with a mass fractionating section that selectively separates ions and a detector that detects each ion mass-separated in this mass fractionating section has the following configuration.

That is, the gas chromatograph mass spectrometer of the present invention includes an intensity ratio calculation section that calculates the intensity ratio of detection signals detected by the detector as channels are switched, and a calculation result of this intensity ratio calculation section that is set in advance. and a comparison/discrimination unit that determines the magnitude of the detected signal by comparing it with the determined threshold, and a comparison/discrimination unit that determines the level of the detection signal only when the intensity ratio is less than or equal to the threshold. and a level control section that outputs a correction signal to maintain the baseline.

(e) Effect In the above configuration, the intensity ratio calculation unit calculates the intensity ratio of the detection signals detected by the detector as the channels are switched. The comparison/determination section compares this intensity ratio with a preset threshold value to determine its magnitude. Then, the determination result is given to the level control section.

Based on the determination result, the level control section outputs a correction signal that maintains the detection signal at the baseline only when the intensity ratio is less than or equal to the threshold value, and outputs a correction signal that maintains the detection signal at the baseline when the intensity ratio is less than or equal to the threshold value. No output.

Therefore, if ghost peaks appear simultaneously at the same retention time for mass fragmentograms with different m/z, or if there is no peak at all in any of the mass fragmentograms, the detection signal Changes in the level of are canceled out and maintained at the baseline. On the other hand, if a peak of a gas actually separated by the gas chromatograph exists, the peak of the corresponding component gas appears as it is in the mass fragmentogram measured by the MP.

(F) Embodiment FIG. 1 is a block diagram of a gas chromatograph mass spectrometer according to an embodiment of the present invention. In the figure, reference numeral 1 indicates the entire gas chromatograph mass spectrometer, 2 indicates a gas chromatograph that separates the sample gas (here, 0.0 gas containing impurity gases such as Ht 01 Co and COz) into the gas phase, and 4 indicates the gas chromatograph. 6 is an interface provided between the gas chromatograph and the mass spectrometer. The mass spectrometer 4 includes an ion source 8 that ionizes gas, and a mass fractionator 1 that separates ions by mass.
0, a detector I2 for detecting ions mass-separated by the mass separation unit 10 is provided. 14 is the number of channels, m/z
(m is a mass number, Z is a charge), an offset amount for background removal, and a threshold value serving as a reference for a comparison/determination section to be described later. The input section is configured of, for example, a keyboard. (2) 6 is a switching signal generation unit that outputs a channel switching signal according to the number of channels set in the input unit 14; 18 is an m/z rara that holds m/z data set in the input unit 14; 20 is m
/z latch unit ■Converts the m/z value held in 8 into a corresponding analog applied voltage control signal and outputs it.
The /z control signal output section 22 is a first switching section that switches the applied voltage control signal from the m/z control signal output section in response to the channel switching signal from the switching signal generation section I6. 24 is a first amplifier that amplifies the detection signal from the detector 12; 26 is an adder that superimposes each output signal of an offset signal output section and a level control section, which will be described later, on the output of the first amplifier 24; 28 is an adder 26; A to digitize the output of
30 is a signal reading unit that reads the A/D converted detection signal, 32 is a second switching unit that selects and switches the detection signal for each channel in synchronization with the channel switching signal, and 34 is a recorder. be.

36 is an offset launch unit that latches the offset amount for background removal set by the input unit 14; 38;
40 is an offset signal output unit that converts the offset amount latched by the offset latch unit 36 into a corresponding analog signal and outputs it; This is the third switching section that switches the switch.

42 is a threshold latch unit that latches the threshold value set by the input unit I4; 44 is a fourth switching unit that selects each detection signal read by the signal reading unit 30 in synchronization with the channel switching signal; and 46 is a an intensity ratio calculation unit 48 that calculates the ratio of detection signals obtained with each channel switching;
Reference numeral 50 indicates a comparison/discrimination unit that compares the calculation result of the intensity ratio calculation unit 46 with the threshold value latched by the threshold latch unit and determines the magnitude thereof. A level control section 52 outputs a correction signal to maintain the level of the detection signal from the detector I2 at the baseline only when the ratio is below a threshold value, and a level control section 52 controls the output of the level control section 50 in synchronization with the channel switching signal. The fifth switching section 54 is a D/A converter that converts both the outputs of the third and fifth switching sections into analogs, and the reference numeral 56 is a second amplifier that amplifies the output of the D/A converter 54.

Next, in the gas chromatograph mass spectrometer 1 having the above configuration, 0. Control operations when analyzing impurity gases contained in gas and measuring mass fragmentograms will be described. In this example, in order to simplify the explanation, a case will be described in which only CO and 002 gas are analyzed as impurity gases.

In advance, input unit I4 sets m/z=2 for CO gas.
8, CO and gas are set to m/z=4.4, and the channel is set to "2" correspondingly. Further, with reference to other measured values, etc., the offset amount for background removal and the threshold value to which the intensity ratio of the detection signal is compared are respectively set. Each value set by these input sections 14 is latched by the m/z latch 18, the offset latch section 36, and the threshold latch section 42, respectively.

When analysis is started, 02 gas containing impurity gas (CO+C02) is introduced into the gas chromatograph 2, separated into a gas phase, and then introduced into the ion source 8 via the interface 6. After being ionized by the ion source 8,
It is guided to the mass fractionating section IO. In addition, the switching signal generator 16
For example, a channel switching signal is output every 20mm5ec, and this channel switching signal is used for the first to fifth channels.
Since this signal is also applied to the switching units 22, 32, 40, 44, and 52, the first to fifth switching units switch in synchronization with this signal. Therefore, first, from the III/Z control signal output section 20, the analog applied voltage control signal corresponding to each m/z (-28, 44) value latched by the m/z latch section 18 is outputted as the first switching signal. outputted through the section 22,
This is given to the mass fractionator 10. this? As a result, the accelerating voltage applied to the mass sorting section 10 is switched in synchronization with the channel switching signal, and
Only the ion (Go, C07) with /z (=28.44) is selectively detected by the detector 12.

On the other hand, the third switching section 40 selectively switches the output of the offset signal output section 38 in synchronization with the channel switching signal, so that the offset signal latched in advance by the offset latch section 36 is transferred from the third switching section 40 to the /A converter 5
4. The signals are sequentially outputted via the second amplifier 56 and applied to the adder 26. Since the adder 26 superimposes the offset signal on the detection signal from the first amplifier 24, the adder 26
A detection signal whose signal level has been lowered by an amount corresponding to the background is outputted from the detector 26 for each channel.

Furthermore, the output of the adder 26 is digitized by the A/D converter 28, and then is given to the intensity ratio calculation F446 via the signal reading section 30 and the fourth switching section 44.

Therefore, the intensity ratio calculation unit 46
The intensity ratio of the detected signals for each channel read in is calculated. That is, the ion of m/z-28 (
CO) detection signal level ■. , if the level of the detection signal of the ion (c O2) with m/z = 4.4 is 1, then
The intensity ratio calculation unit 46 is I. /II is calculated. The value of this intensity ratio is sent to the comparison/discrimination section 48, so the comparison/discrimination section 48 calculates this intensity ratio (■). /r1 is compared with a preset threshold value S to determine its magnitude. And the strength ratio ■
. When /■t is less than the threshold value S (to/i+≦S), a high-level discrimination signal is output in this example. Also,
intensity ratio r. /[, is larger than the threshold S (■o
/i>S), a low level discrimination signal is output.

These discrimination signals are given to the level control section 50 at the next stage. When the level control unit 50 receives a high-level discrimination signal, it determines that there is a possibility that a ghost beak may occur, and outputs correction signal data that maintains the detection signal at the baseline. This correction signal data is given to the adder 26 via the fifth switching section 52, the D/A converter 54, and the second amplifier 56. In this case, the adder 2G superimposes both the offset signal from the third switching section 40 and the correction signal from the fifth switching section 52 on the detection signal output of the first amplifier 24. Therefore, the adder 26 outputs a detection signal in which the signal level is lowered by an amount corresponding to the background, and the level change caused by the ghost peak is canceled out. Further, when a low level signal is output from the comparison/discrimination section 48 to the level control section 50, the level control section 50 determines that there is a peak of ions of the gas (Go, Go,) separated by the gas chromatograph. In this case, the equivalence correction signal is not output. Therefore, in this case, adder 26
A detection signal from which only the background has been removed is output.

Then, the detection signal from the adder 26 is sent to the signal reading section 30.
, is applied to the recorder 34 via the second switching section 32. Therefore, as shown in Figure 2, when measuring the total ions (gas chromatogram) (see figure (a)), the recorder 34 has a , m/z (=28.44) (Figure (b), (C
), CO and C do not have ghost peaks.
Each peak of O2 will be recorded.

(l・) Effect According to the present invention, 0. H20 in gas.

When analyzing impurity gases such as CO1CO2, the intensity ratio of the detection signal for each channel is monitored, and if the intensity ratio is below the threshold, the level change of the detection signal is offset to maintain the baseline. As a result, ghost peaks resulting from the reaction between 02 gas and hydrocarbons no longer appear in the measured mass fragmentogram. Therefore, as in the past, ghost peaks cannot be compared to true CO or C.
The erroneous recognition as an O2 ion peak and the deterioration in the accuracy of quantitative calculations are eliminated, and excellent effects such as always obtaining highly accurate analysis results are exhibited.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a gas chromatogram/graph mass spectrometer according to an embodiment of the present invention, Figure 2 is a gas chromatogram and mass fragmentogram measured with the same equipment, and Figure 3 is a gas chromatogram obtained with a conventional equipment. tograms and mass fragments) and grams. 1 Gas chromatograph mass spectrometer, 10 mass fractionation section, ■2...detector, I6... switching signal generation section, 46
- Intensity ratio calculation unit, 48 - Comparison/discrimination unit, 50...Level control unit.

Claims (1)

[Claims] (1) A switching signal generation section that generates a channel switching signal, a mass separation section that selectively separates ions with a corresponding mass number in synchronization with this channel switching signal, and each ion mass separated by this mass separation section. In a gas chromatograph mass spectrometer equipped with a detector for detecting a a comparison/discrimination unit that compares the calculation result with a preset threshold value to determine its magnitude; and based on the discrimination signal from the comparison/discrimination unit, the detection signal is output only when the intensity ratio is equal to or less than the threshold value. A gas chromatograph mass spectrometer, comprising: a level control unit that outputs a correction signal to maintain the level of at a baseline;