JPH0968521A - Photo-ionization sensor for gas-chromatograph - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress sensivity drop of a sensor to possible minimum by setting the lighting timing of a light source of a photo-ionization sensor (PID) on the basis of the point of time at which a sample is introduced to a separation column of a gas-chromatograph. SOLUTION: The lighting timing of a light source, for example ultraviolet lamp, of a PID is set on the basis of the point of time at which a sample is introduced to a separation column of a gas-chromatograph. The put-off timing of the light source is set to after the last analytical component peak appears on the chromatograph on the basis of the point of time at which sample is introduced to the separation column. The light source is lighted up for necessary time each time measurement is made, and it is arranged so that the light source is lighted intermittently if viewed on the long-term basis. Thereby the lifetime of the light source can be prolonged, and premature drop of the sensitivity due to continuous use can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoionization detector for a gas chromatograph (hereinafter, abbreviated as PID, if necessary), and more specifically, to a lifetime of a light source and a decrease in detection sensitivity over time. The present invention relates to a photoionization detector that is suppressed to the limit.

[0002]

2. Description of the Related Art PID is used as a detector for a gas chromatograph such as FID (hydrogen flame ionization detector) or FPD.
It is well known along with (flame photometric detector). 5 is P
1 is a schematic configuration diagram of an ID, in which 31 is a detection cell, 32 is an ionization chamber, 33 is a pair of electrodes, 34 is an electrometer connected to the electrodes 33, and 35 is a separation column (not shown). A sample introduction pipe connected to the outlet, 36 is an exhaust pipe, 37 is an ultraviolet lamp as a light source, and 38 is a lamp 3.
It is a cell window that allows the ultraviolet rays from 7 to pass through in the direction of the ionization chamber 32.

In the above structure, the analytical components in the sample separated by the separation column are introduced into the ionization chamber 32 through the introduction pipe 35 by carrying the carrier gas, and are absorbed by the ultraviolet rays from the ultraviolet lamp 37 to be ionized. The ions generated by this are collected in the electrode 33, and the electrometer 34
Is amplified and detected as the concentration of each analytical component.

[0004]

Here, it is conventionally known that the detection sensitivity gradually decreases as the lighting time of the ultraviolet lamp 37 increases. As a cause for this, it is considered that the amount of ultraviolet rays reaching the ionization chamber 32 is reduced due to, for example, deformation of the discharge electrode in the lamp or adhesion of various products to the inner wall of the lamp and the cell window 38.

FIG. 6 shows three kinds of volatile organic compounds (○,
(Indicated by □, △) as the analysis component, the cumulative lighting time of the ultraviolet lamp and the relative sensitivity on the detector side (for each component, the initial peak value on the chromatogram was set to 1.0)
It can be seen that the sensitivity decreases almost linearly as the integrated lighting time increases. Here, an ultraviolet lamp having various characteristics is selected according to the analysis component, but the tendency of decreasing the sensitivity as shown in FIG. 6 is general regardless of the type of the ultraviolet lamp.

Therefore, when performing the analysis by continuously using the ultraviolet lamp, it is necessary to correct the output of the detector so as to compensate the above-mentioned sensitivity deterioration, and the degree of the correction directly affects the analysis value. , It also affects the analysis accuracy. In order to avoid such a complicated correction, it is sufficient to replace the ultraviolet lamp in a short period of time or frequently clean the cell window, but this causes a new economical burden and labor problems.

Focusing on these points, a PID equipped with a lamp saver means for extending the life of an ultraviolet lamp is disclosed in Japanese Patent Publication No.
It is disclosed in Japanese Patent No. 58282. In this lamp saver means, a timer operates to stop the power supply to the ultraviolet lamp when an arbitrary time set by the user elapses after the ultraviolet lamp is turned on.

However, in this prior art, the extinguishing time is preset in order to prevent the life of the ultraviolet lamp from being shortened due to forgetting to turn off the ultraviolet lamp, and it is assumed that the measurement is performed in a relatively short time or the same sample is repeatedly measured. No, it does not specifically mention the timing of lighting.

Therefore, the present invention is intended to suppress the deterioration of the detection sensitivity to a minimum by appropriately setting the timing of turning on / off the light source, rather than largely depending on the correction of the detector output. .

[0010]

In order to solve the above problems, in the invention according to claim 1, the lighting timing of a PID light source, for example, an ultraviolet lamp, is based on the time when a sample is introduced into a separation column of a gas chromatograph. Set as. Further, in the invention described in claim 2, in addition to the above, the turn-off timing of the light source is set after the peak of the last analytical component appears on the chromatogram with reference to the time when the sample is introduced into the separation column.

By setting the timing of turning on / off the light source as described above, the light source is turned on for a necessary time for each measurement, and the light source is turned on intermittently when viewed on a long time scale. To do so. As a result, it is possible to extend the life of the light source and prevent the sensitivity from being lowered early due to continuous use. Also, after the light source is turned on, P
After the ID operation is almost stable, the first peak value of the analysis component appears on the chromatogram, and improvement in analysis accuracy can be expected.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an example of a timing chart showing the timing of turning on / off the ultraviolet lamp according to the embodiment of the present invention. For example, when analyzing a volatile organic compound or the like, a concentration tube for collecting and concentrating the organic compound is provided in the preceding stage of the gas chromatograph. As shown in FIG. 1, before introducing the sample into the separation column (for example, 5
When the concentration tube is heated and the carrier gas is supplied (from the minute before), the concentrated analytical components are desorbed and introduced as a sample into the separation column of the gas chromatograph.

Assuming now that the time when the sample is introduced into the separation column is the reference time point (time 0 minutes), in this embodiment, as shown in FIG.
As shown in, the ultraviolet lamp is turned on 3 minutes before the reference time point, and the ultraviolet lamp is turned off after the peak due to the last analytical component appears on the chromatogram (52 minutes after the reference time point in the example of FIG. 1). It was decided to.

FIG. 2 is an explanatory diagram of a chromatogram showing the analysis result according to this embodiment, in which the ultraviolet lamp is turned on 3 minutes before the sample is introduced into the separation column and each component is separated and analyzed. is there. Although not shown in the figure, the timing of turning off the ultraviolet lamp is set after the peak of the last analytical component appears on the chromatogram with reference to the sample introduction time.

In FIG. 2, the detector output is unstable immediately after the ultraviolet lamp is turned on, but if the sample is introduced after 3 minutes have passed since the lamp was turned on, the operation of the detector is almost stable. It can be seen that after the peak of the first analytical component appears, the baseline is almost stable and each peak can be accurately detected.

On the other hand, FIG. 3 is an explanatory view for the same sample when the ultraviolet lamp is turned on at the same time when the sample is introduced into the separation column, and shows the peaks in the state where the operation of the detector is not yet stable. It is clear that the shape is quite different from that of FIG.

Next, the upper part of FIG. 4 shows, according to this embodiment, the total measurement time when the ultraviolet lamp is intermittently turned on at the timing of turning on and off for each measurement,
It is a figure which shows the integrated lighting time of an ultraviolet lamp (it describes with the number in () near each plot), and relative sensitivity. In addition, a timing chart of turning on / off the ultraviolet lamp at each measurement is also shown in the lower part of FIG.
Here, the analysis component is fluorobenzene.

By setting the timing of turning on / off the ultraviolet lamp as described above, as shown in FIG. 4, the detection sensitivity sometimes recovers from the previous time.
As a general tendency, it can be seen that the decrease in sensitivity is slower than before. In the present invention as well, the decrease in detection sensitivity has not been completely eliminated, so it is also effective to compensate for the decrease in sensitivity by correction if necessary.

In the above description, the on / off timing of the ultraviolet lamp is set with the direct introduction of the sample into the separation column as a reference. However, it is an analyzer that desorbs analytical components by heating the concentrating tube provided in the previous stage of the gas chromatograph and sends them to the separation column, and the timing of starting heating of the concentrating tube is set based on the time of sample introduction. For the case where the start of heating the concentrating tube is set 5 minutes before the sample introduction as shown in FIG. 1, the ultraviolet lamp is turned on with the timing of starting the heating of the concentrating tube as a direct reference. The turn-off timing may be set. That is, in this case, the lighting and extinguishing timings are set with the sample introduction as an indirect reference.

The light source for PID in the present invention is not limited to the ultraviolet lamp, and may be a lamp having another wavelength region depending on the analysis component.

[0021]

As described above, according to the present invention, it is possible to prevent the life of the light source from being shortened at an early stage due to continuous use, to minimize the sensitivity deterioration of the detector, and to correct the detector output. Even if it is not necessary, it is possible to obtain an analysis accuracy that is practical enough. Moreover, since the frequency of replacing the light source and the frequency of cleaning the cell window can be reduced, it is highly economical and convenient for maintenance and inspection.

[Brief description of drawings]

FIG. 1 is a timing chart showing the timing of turning on and off an ultraviolet lamp according to an embodiment of the present invention.

FIG. 2 is an example of a chromatogram according to an embodiment of the present invention.

FIG. 3 is an example of a chromatogram when an ultraviolet lamp is turned on at the same time when a sample is introduced.

FIG. 4 is a diagram showing the relationship between the total measurement time, the cumulative lighting time of the ultraviolet lamp and the relative sensitivity, and the lighting / extinguishing timing of the ultraviolet lamp according to the embodiment of the present invention.

FIG. 5 is a schematic configuration diagram of a PID.

FIG. 6 is a diagram showing a relationship between integrated lighting time of an ultraviolet lamp and relative sensitivity.

[Explanation of symbols]

 31 Detection Cell 32 Ionization Chamber 33 Electrode 34 Electrometer 35 Introducing Pipe 36 Exhaust Pipe 37 Ultraviolet Lamp 38 Cell Window

Claims (2)

[Claims] 1. A photoionization detector for a gas chromatograph, characterized in that a lighting timing of a light source for ionizing an analysis component in the sample is set with reference to a time point when the sample is introduced into a separation column of the gas chromatograph. 2. The photoionization detector for a gas chromatograph according to claim 1, wherein the peak of the last analytical component appears on the chromatogram with reference to the timing of turning off the light source based on the time point when the sample is introduced into the separation column. A photoionization detector for a gas chromatograph, which is set later.