JP2984894B2 - Gas chromatograph peak measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring peaks in a gas chromatograph.

[0002]

2. Description of the Related Art In general, in a gas chromatograph, a fixed amount of a mixed sample, which is a sample gas, is charged into a column filled with an appropriate stationary phase and constantly flowing a carrier gas as a mobile phase. It analyzes the components. That is, in this case, the sample gas is swept toward the outlet of the column by the carrier gas, and the moving speed of each component of the sample gas is determined by the affinity with the stationary phase. And the time and order until each component separated by the stationary phase is delivered to the outlet of the column,
The qualitative and quantitative analysis of the sample gas is performed based on the voltage signal of each component detected and output by the detector.

A voltage signal detected by such a detector is converted into a signal having a frequency corresponding to the level by a V / F converter for converting a voltage into a frequency. When the count value of the frequency signal is detected and plotted at a constant period, a peak P indicating the component of the sample gas as shown in FIG. 4 can be obtained. In the drawing, ton indicates the time point at which the peak P is measured (rise time), t0ff indicates the time point at which the peak P is measured (fall time), and BL and BL 'indicate the baseline of the peak P. I have.

Here, when calculating the peak area PA, which is the area of the peak P, first, the measurement start time t of the peak P is calculated.
On and the measurement end time t0ff are uniquely determined, the count value of the frequency signal between each time point is detected and integrated at a constant period, and the area is obtained from the integrated value, as shown in FIG. It is calculated as the entire area S1. Next, from the entire area S1, FIG.
The peak area A is obtained by subtracting the area S0 of the triangular portion shown in FIG.
Is calculated. After the peak area is calculated in this way, quantitative analysis of the sample gas is performed based on the calculated peak area.

[0005]

Conventionally, when calculating the peak area PA, the measurement start time ton of the peak P and the measurement end time t0ff of the peak P are uniquely determined, and the total area S1 is obtained at this measurement timing. In addition, since the calculation is performed by subtracting the area S0 of the portion below the base line BL from the entire area S1, the following problem occurs. That is, when the base line fluctuates in a curved line like the base line BL ′ shown in FIG. 4, the peak area PA calculated based on the linearly fluctuating base line BL is shown in FIG. An error as shown occurs. The error due to such a baseline variation has a problem that the ratio of the measurement error is particularly large when the level of the peak P is low as in the case of a low concentration gas.

Accordingly, an object of the present invention is to accurately calculate a peak area while minimizing an error when a baseline fluctuates in a curved line, and to accurately perform quantitative analysis of a sample gas.

[0007]

SUMMARY OF THE INVENTION In order to solve such a problem, the present invention detects each component of a sample gas flowing through a column, converts the detected component into a voltage signal, and converts the component to a peak level indicating the voltage signal. Generate a frequency signal according to
When the count value of the frequency signal is detected at a fixed period between the first and second time points indicating the start and end of the peak measurement, the count values are integrated, and the peak area is calculated from the integrated value. The reference measurement range information of the peak is stored in the memory in advance,
Corresponding to the reference measurement range information, first and second reference time information indicating respective reference time points of the start and end of the peak measurement are stored, and the difference between the peak measurement range and the reference measurement range at each reference time point is stored. First and second coefficients indicating coefficients are stored, and when the measurement range is set, the first and second time points are calculated from the measurement range information and the respective information previously stored in the memory. This is a peak measuring method in which a peak area is obtained based on a count value of a frequency signal integrated at a constant period between each of the time points.

[0008]

The first and second indicating the start and end of the peak measurement from the measurement range information set in advance by the operator according to the concentration of the gas to be measured and the information stored in the memory in advance.
Is determined, and the peak area is calculated from the count value integrated between these times, so that, for example, a low peak indicating a low concentration gas and a high peak indicating a high concentration gas are measured in the same manner. The measurement is not performed at the timing, and the error based on the curve variation of the baseline is reduced particularly when the low concentration gas is measured, so that the peak area can be calculated with high accuracy.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an apparatus to which a method for measuring a peak of a gas chromatograph according to the present invention is applied. In FIG. 1, 1 is a sample gas, and 2 is a TCD that detects a component of the sample gas 1 and outputs it as a voltage signal.
Sensor 3, a constant current circuit for supplying a constant current to the TCD sensor 2, 4, 6 an amplifier circuit, 5 an addition circuit, 7
Is a V / F converter that outputs a frequency signal according to the level of the input voltage signal, 8 is a counter, 9 is a CPU,
0 is a gain switching unit that switches the gain of the amplifier circuit 6;
11 baseline canceling unit that cancels the baseline voltage signal, 12 is an E ² PROM capable of electrically writing and erasing.

Next, the operation of the above device will be described. Each component of the sample gas 1 transported by the carrier gas in the column (not shown) is detected by the TCD sensor 2 and output as a voltage signal. This voltage signal is amplified by the amplifier circuit 4 and output to one input terminal of the adder circuit 5. The addition circuit 5 adds the voltage signal and a voltage signal for canceling the baseline voltage input from the other input terminal, cancels the baseline voltage of the input voltage signal, and outputs the same to the amplifier circuit 6. The amplifier circuit 6 amplifies the voltage signal from the adding circuit 5 according to the switching gain value of the gain switching unit 10 and outputs the amplified voltage signal to the V / F converter 7. The V / F converter 7 receives a voltage signal from the amplifier circuit 6 and generates a frequency signal according to the level. The frequency signal is counted by the counter 8, and the CPU 9 reads the counted value at a constant cycle to perform a qualitative analysis of a gas component in the sample gas 1.

That is, the CPU 9 reads the count value of the counter 8 at a constant period from the start of the measurement of the voltage signal, ie, the peak to the end of the measurement, and integrates the count. The peak area is determined from the count value, and the qualitative analysis of the sample gas 1 is performed. Here, as shown in FIG. 2, the height and width of the peak waveform differ depending on the concentration (vol%) of the sample gas, and the height and width increase as the concentration increases. Therefore, the time between the measurement start time and the measurement end time of the peak P4 when the concentration is, for example, 10 (vol%) is shorter than the peak P1 when the concentration is 100 (vol%). By the way, when the low-concentration gas indicated by the low-level peak P4 is measured at the same timing as the high-concentration gas indicated by the high-level peak P1, if the base line fluctuates like a curve BL 'in the figure, In the low-level peak P4, the ratio of the fluctuation part of the baseline becomes large, and therefore, the error of the peak area becomes large.

For this reason, in this embodiment, the gates for P1, P2,... In FIG. 2 are obtained from measurement range information and the like which will be set in advance by the operator according to the measured gas concentration.
The time between the measurement start time and the measurement end time of the peak represented by the above, that is, the measurement timing is determined. Then, the area of the peak P is calculated by detecting and integrating the count value of the counter 8 at a fixed period during the determined measurement timing.

FIG. 3A is an explanatory diagram showing a situation in which the above-mentioned peak measurement timing is determined. Where t
on is the peak measurement start time (first time) and tof
f indicates a peak measurement end point (second point), and the measurement start point ton and the measurement end point toff are determined according to the levels of the peaks P1 to P3 which are voltage signals corresponding to the concentration of the measurement gas. That is, in FIG. 3B, the horizontal axis is the measurement range of the peak P, and the vertical axis is the time axis, that is, the peak P.
Let us consider the case where the measurement start time and the measurement end time are used.
In this case, a measurement start reference time point ton0 (first reference time point) and a measurement end reference time point toff0 (second reference time point) are provided on the vertical axis corresponding to the reference measurement range R0 on the horizontal axis. Next, assuming that the measurement range is R, information indicating how much the measurement start time ton corresponding to this measurement range R deviates from the measurement start reference time ton0, that is, the measurement at the measurement start time ton Assuming that the coefficient of the difference between the range R and the reference measurement range R0 is a, the measurement start time ton corresponding to the measurement range R can be expressed by equation (1). ton = ton0 + a (R-R0) (1)

Further, information indicating how much the measurement end time toff corresponding to the measurement range R deviates from the measurement end reference time toff0, ie, the measurement end time toff
Assuming that the coefficient of the difference between the measurement range R and the reference measurement range R0 in the off state is b, the measurement end time toff corresponding to the measurement range R can be expressed by equation (2). toff = toff0 + b (R-R0) (2)

In the above equations (1) and (2), the peak measurement start reference time ton0 and the measurement end reference time tof
The value f0, the coefficients a and b, and the reference measurement range R0 are stored in the electrically erasable E ² PROM 12 in advance. The measurement range R is provided to the CPU 9 as information set by the operator. Therefore, the CPU 9
When the peak is measured, each information in the E ² PROM 12 is read out, the measurement range R set by the operator is input, the arithmetic processing shown in the equations (1) and (2) is executed, and the peak measurement is started. Time point ton and measurement end time point tof
Calculate f. Then, the peak area between the calculated time points ton and toff is obtained, and the measurement and analysis of each component of the sample gas is performed.

As described above, the preset E ² PROM
The peak measurement start time ton and the measurement end time toff can be determined based on the information in the area 12 and the measurement range information set by the operator. That is, when the concentration of the gas to be measured is low and the level of the peak is low, as shown by the gate for P4 in FIG. Set the measurement timing so that is shorter. If the concentration of the gas to be measured is high and the peak level is high,
As shown as a gate for P1 in FIG. 2, the measurement timing is set so that the measurement start time ton is earlier and the measurement end time toff is later, so that the time between each measurement time ton and toff becomes longer. As a result of determining the measurement timing of the peak P in this manner, even if the baseline fluctuates in a curved line, the error in the calculation of the peak area is small, and therefore, the sample gas can be measured accurately.

As described above, in the present invention, the measurement timing is determined according to the level of the concentration of the sample gas. However, this can be applied to the following examples. That is, when the gain of the amplifier circuit 6 is switched by the gain switching unit 10 when the concentration of the sample gas is low and the peak level is low, and the peak level is increased, the baseline also fluctuates and is calculated. An error occurs in the peak area. Even in such a case, if the present invention is applied, the respective time points ton and toff can be accurately determined, and therefore, the peak area can be accurately calculated.

[0018]

As described above, according to the present invention,
Measurement range information set in advance by an operator according to the concentration of the gas to be measured, reference measurement range information of a peak previously stored in a memory, and first and second reference time point information corresponding to the reference measurement range information. First and second time points indicating the start and end of the peak measurement are determined from each information, and the peak area is calculated based on the count value integrated between these time points. The low peak and the high peak indicating the high concentration gas are not measured at the same measurement timing,
Therefore, when measuring a low-concentration gas, the error based on the curve fluctuation of the baseline is reduced, and the peak area can be calculated with high accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram of an apparatus to which a method for measuring a peak of a gas chromatograph according to the present invention is applied.

FIG. 2 is a diagram showing a measurement situation of each peak indicating a gas concentration in the above-mentioned device.

FIG. 3 is an explanatory diagram showing a calculation state of a peak measurement timing in the above device.

FIG. 4 is a diagram showing timing of a conventional peak measurement.

FIG. 5 is a diagram showing a conventional peak area calculation situation.

[Explanation of symbols]

1 Sample Gas 2 TCD sensor 3 constant current source 4, 6 amplifiers circuit 5 adding circuit 7 V / F converter 8 counter 9 CPU 10 gain switcher 11 baseline canceling section 12 E ² PROM R measured range information

Claims (1)

(57) [Claims] 1. A method for detecting each component of a sample gas flowing through a column, converting the detected component into a voltage signal, generating a frequency signal corresponding to the level of a peak indicating the voltage signal, and starting and ending the measurement of the peak. Between the first and second time points shown, the count value of the frequency signal is detected at regular intervals, and the count values are integrated. The area of the peak is calculated from the integrated value to measure and analyze the sample gas. In the gas chromatograph, the reference measurement range information of the peak and the first and second reference time information indicating the reference start and end of the peak measurement corresponding to the reference measurement range information are stored in advance in the memory. And the first and second coefficients indicating the difference coefficient between the peak measurement range and the reference measurement range at each of the reference times are stored, and the measurement range is set. The first and second time points are calculated from the measurement range information and the information stored in the memory, and the peak area is calculated based on the integration of the count value of the frequency signal between the calculated time points. A method for measuring a peak of a gas chromatograph, wherein the peak is determined.