JPH08338833A - Gas chromatograph - Google Patents

Abstract

PURPOSE: To immediately execute the adjustment of supplying pressure of a gas by a method wherein a specimen gas is measured at a plurality of predetermined carrier gas-supplying pressures to obtain a relationship between the carrier gas supplying pressures and maintaining time periods and the carrier gas pressure of which maintaining time period becomes constant by virtue of the specimen gas is calculated in accordance with the relationship. CONSTITUTION: In a carrier pressure adjustment section 9, a carrier pressure P1 greater than a desired carrier pressure and a carrier pressure P2 lower than the desired carrier pressure are prepared, a pressure reducing valve 1 of a pressure reducing control section 3 is controlled so that the carrier pressures are set to the pressures P1, P2. After the carrier pressures P1, P2 are normalized, an analyzer valve 4 is driven by the adjustment section 9, then a prescribed quantity of the specimen gas is introduced into a column 5 and a peak representation times Rt1, Rt2 of the specimen gas by the carrier pressures P1, P2 are stored in a memory. Next, the desired carrier pressure Psp is obtained in accordance with an equation of Psp=(Rtsp-Rt1)×(P2-P1)/(Rt2-Rt1)+P1. Rtsp is a center of a band of gate time determined by a component of the specimen gas. The adjustment section 9 sets the carrier pressure Psp to a control section 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas chromatograph for analyzing a gas by utilizing the fact that the movement of a mobile phase passing through a stationary phase causes a difference in the movement of the mobile phase. The present invention relates to a gas chromatograph that automatically adjusts.

[0002]

2. Description of the Related Art In a petrochemical process, a steel process, etc., a gas chromatograph is used as a detector for analyzing the components of a process gas, monitoring each process step based on the analysis result, and performing various controls. Has been used conventionally. In this gas chromatograph, a carrier gas and a sample gas are mixed, and based on a concentration signal waveform that is a peak of a chromatogram showing a measured gas component contained in this mixed gas that appears in a predetermined gate time zone, The concentration of the measured gas component is measured.

FIG. 3 is a chromatogram showing an example of measurement results obtained by gas chromatograph measurement. In the figure, the peak 31 of the component to be measured appears within the gate time zone 32 for determining the component.
The appearance position (holding time) of the peak 31 is a state peculiar to the component to be measured. In other words, the appearance of the peak 31 in the gate time zone 32 makes it possible to qualify this component.

By the way, the appearance position of the peak 31 is
It changes depending on the state of the column. Further, if the supply pressure of the carrier gas changes, the appearance position also changes. Therefore, normally, when the gas chromatograph is manufactured or the column is replaced, the gas chromatograph is adjusted as shown below. First, a sample gas for adjustment containing a predetermined component whose concentration is known is measured by a gas chromatograph to be adjusted. Then, the supply pressure of the carrier gas is adjusted so that the peak showing the component in the chromatogram obtained at this time falls within a predetermined position, that is, the gate time zone for identifying the component.

[0005]

[SUMMARY OF THE INVENTION However, the regulation of the supply pressure of such carrier gas (carrier pressure) are not known whether it is appropriate if the extent to which advance. For this reason, the above-mentioned adjustment is performed by trial and error, as shown below. First, the carrier pressure at which the target peak is considered to appear near the target gate time zone is set, and the component analysis of the sample gas is performed. Here, the appearance position of the peak in the resulting chromatogram does not normally fall within the gate time zone. In most cases, it appears earlier or later than the gate time.

For this reason, when the gas appears earlier than the gate time, the carrier pressure is lowered, and the component analysis of the sample gas is again performed in the same manner to confirm the appearance position of the peak.
In addition, when the appearance appears later than the gate time zone, the carrier pressure is increased, the component analysis of the sample gas is again performed in the same manner, and the appearance position of the peak is confirmed. Then, by repeating these operations, when the peak appearance position enters the gate time zone, the carrier pressure is finally finely adjusted so that the peak appearance location becomes the center of the gate time zone.

As described above, in the past, manual adjustment was performed depending on the intuition of the operator. Therefore, in some cases, the above-mentioned work of setting the carrier pressure-measuring-confirming to obtain the desired carrier pressure is repeated a plurality of times, and there is a problem that the adjustment takes a very long time.

The present invention has been made to solve the above problems, and an object of the present invention is to make it possible to quickly adjust the supply pressure of a carrier gas.

[0009]

A gas chromatograph according to the present invention comprises a carrier pressure setting means for setting a plurality of different carrier gas supply pressures to a decompression control section, and a plurality of carrier gas supply pressures set by the carrier pressure setting means. In the above, the gas chromatograph is used to measure the sample gas, the resulting correlation between each carrier gas supply pressure and the holding time at that time is calculated, and the predetermined holding by the sample gas is performed so as to match this correlation. It is characterized in that it is provided with a carrier pressure adjusting section comprising a carrier pressure calculating means for calculating a carrier gas pressure which becomes time.

[0010]

By operating the carrier pressure adjusting section, the pressure of the carrier gas that matches the characteristics of the column is automatically obtained.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing the configuration of a gas chromatograph in one embodiment of the present invention. In the figure, 1
Is a pressure reducing valve for reducing the pressure of the supplied carrier gas, 2 is a pressure detecting unit for detecting the pressure of the carrier gas coming out of the pressure reducing valve 1, and 3 is the operation of the pressure reducing valve 1 using the value detected by the pressure detecting unit 2. The pressure reducing valve control unit 4 for controlling is an analyzer valve for switching the flow path between a state in which only the carrier gas is flowing and a state in which the gas to be analyzed is flowing in addition to this, 5 is a column, 6 is separated by the column 5. And a detection unit for detecting the concentration of each component of the analysis target gas. The analyzer valve 4 operates using the pressure of the supplied carrier gas. Then, 7 is an A / D conversion unit, 8 is a control unit, and 9
Is a carrier pressure adjusting unit.

In the above structure, the density signal detected and output by the detector 6 is converted into a digital signal by the A / D converter 7 and input to the controller 8. In the control unit 8,
From the change in the input concentration signal, for example, the maximum value of the peak waveform in the chromatogram is obtained. Also, the holding time from the start of measurement to the appearance of this maximum value is monitored.
Then, these data are displayed and output to a display unit (not shown). Then, the control unit 8 controls the operation of the pressure reducing valve control 3 by giving a set value SP of the carrier pressure to the pressure reducing valve control unit 3, and also controls the flow path changing operation of the analyzer valve 4.

In this gas chromatograph, the control unit 8 activates the carrier pressure adjusting unit 9 by setting the carrier pressure adjusting mode. Then, the activated carrier pressure adjusting unit 9 automatically sets a desired carrier pressure as described below. In addition, when the carrier pressure adjustment mode is set, the sample gas of which the component and the concentration are known is continuously supplied. First, the carrier pressure adjusting unit 9 sets the set value SP so that the carrier pressure becomes P1. The carrier pressure P1 is a predetermined value higher than the desired carrier pressure. Details of how to obtain this value will be described later.

By setting the carrier pressure P1, the pressure reducing valve control unit 3 controls the pressure reducing valve 1 so that the carrier pressure detected by the pressure detecting unit 2 becomes P1. When the carrier pressure becomes steady in this setting, the carrier pressure adjusting unit 9 operates the analyzer valve 4 to introduce a predetermined amount of sample gas into the column 5. The carrier pressure adjusting unit 9 stores the peak appearance time Rt1 (holding time) of the sample gas at the carrier pressure P1 obtained as a result.

Next, the carrier pressure adjusting section 9 sets the set value SP so that the carrier pressure becomes P2. This carrier pressure P2 is a value smaller than the desired carrier pressure. When the carrier pressure reaches a steady state with this setting, the carrier pressure adjusting unit 9 operates the analyzer valve 4,
A predetermined amount of sample gas is introduced into the column 5. The carrier pressure adjusting unit 9 stores the peak appearance time Rt2 of the sample gas at the carrier pressure P2 obtained as a result.

The carrier pressure adjusting unit 9 uses the holding times Rt1 and Rt2 thus obtained and the carrier pressures P1 and P2 to obtain a desired carrier pressure P _SP from the following equation. P _SP = (predetermined holding time Rt _SP −Rt1) · (P2-P
1) / (Rt2-Rt1) + P1 The predetermined retention time Rt _SP, the center of the gate time period determined by the components of the sample gas.

That is, as shown in FIG. 2, on the coordinates where the horizontal axis represents the carrier pressure and the vertical axis represents the holding time, the point (Rt1,
The characteristic of the target column is linearly approximated by a straight line 21 passing through P1) and the point (Rt2, P2). Then, a point 22 on the straight line 21 which becomes the holding time Rt _SP which is the central value of the gate time zone is obtained, the value on the horizontal axis of this point 22, that is, the carrier pressure is obtained, and the desired carrier pressure P _SP is obtained. To do. Then, the carrier pressure adjusting unit 9 determines the calculated carrier pressure P.
_SP is set in the control unit 8 as the set value SP.

Here, the carrier pressures P1 and P2 are obtained in advance as follows. Since the columns have variations, the carrier pressure at which a peak appears at a holding time earlier than a predetermined gate time zone and the carrier pressure at which a peak appears at a later holding time are obtained for a plurality of columns. Then, for each of them, an average value of the obtained plurality of values is obtained, and these are set as P1 and P2.

As shown above, according to this embodiment,
The carrier pressure that matches the characteristics of the column can be set accurately without relying on human intuition. It should be noted that the measurement of Rt1 and Rt2 is not limited to once, but may be performed a plurality of times and the average value thereof may be used. Also,
In the above example, the obtained Rt1 and Rt2 and P1
And P2 are used to perform linear approximation, but the present invention is not limited to this.

For example, various characteristics of the column of the same type as the column to be used are investigated in advance, and a calculation formula showing an approximate curve by the correlation between the carrier pressure and the state of component elution in this column is prepared. (Rt1, P1), (Rt
2, P2) may be applied to determine the constant and the carrier pressure for a predetermined holding time may be calculated. Also,
It is also possible to set a plurality of set pressures for adjusting the carrier pressure at three or more points instead of two points, and calculate the desired carrier pressure P _SP by a calculation formula showing an approximate curve obtained by measurement by these.

[0021]

As described above, according to the present invention, the carrier pressure adjusting section is newly provided, and as a result, the measurement of the sample gas is performed at a plurality of set carrier gas supply pressures. The correlation between the carrier gas supply pressure and the holding time by the sample gas at that time was obtained, and the carrier gas pressure at which the predetermined holding time by the sample gas was obtained was calculated so as to match this correlation. For this reason, since the gas chromatograph itself automatically adjusts the carrier gas supply pressure, there is an effect that no manual adjustment is required, the adjustment does not take a very long time, and a quick adjustment can be performed.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of a gas chromatograph according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram for obtaining a desired carrier pressure P _SP from a straight line approximating the characteristics of the column 5.

FIG. 3 is a chromatogram showing an example of measurement results obtained by gas chromatograph measurement.

[Explanation of symbols]

1 ... Pressure reducing valve, 2 ... Pressure detecting unit, 3 ... Pressure reducing valve control unit, 4 ...
Analyzer valve, 5 ... column, 6 ... detector, 7 ... A /
D conversion unit, 8 ... Control unit, 9 ... Carrier pressure adjusting unit.

Claims (1)

[Claims] 1. An analyzer valve for switching a flow path between a state in which only a carrier gas is flowing and a state in which a gas to be measured is also flowing, and a pressure of the carrier gas supplied to the analyzer valve is detected. So that the pressure detected by the pressure detector and the pressure detected by the pressure detector become a set value,
A decompression control unit for decompressing the carrier gas supplied to the analyzer valve, a column into which the gas discharged from the analyzer valve is introduced, a detection unit for detecting the concentration of each gas component separated by the column, In a gas chromatograph provided with a control unit for controlling the operation of the decompression control unit by giving a set value or the like, controlling the switching operation of the analyzer valve, and controlling the concentration signal output by the detection unit. Carrier pressure setting means for setting a plurality of different carrier gas supply pressures to the decompression control unit, and a plurality of carrier gas supply pressures set by the carrier pressure setting means, to allow the gas chromatograph to measure the sample gas, Obtain the correlation between each of the resulting carrier gas supply pressures and the holding time at that time. Gas chromatograph, characterized in that it comprises a carrier pressure adjusting unit and means leaving the carrier pressure calculation for calculating a carrier gas pressure as a predetermined holding time by the sample gas to match this correlation.