JPH0122580B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas chromatograph, and more particularly to a gas chromatograph in which a liquid sample can be automatically injected into a sample vaporization section using a syringe.

Autosamplers that aspirate a liquid sample contained in a sample container through the injection needle of a syringe and automatically inject a predetermined amount of sample into the sample vaporization section of a gas chromatograph have traditionally performed sample injection operations at the same time intervals. It was a recurring thing. When such a conventional autosampler is used, ordinary samples containing low-boiling components can be analyzed with high accuracy, but reproducibility of analytical data is poor for samples containing high-boiling components. Moreover, highly accurate analysis results could not be obtained even in the case of highly viscous samples. On the other hand, when the concentration of the component to be analyzed is low, a large amount of sample must be injected into the vaporizer, but when conventional autosamplers are used, separation of chromatographic peaks is poor.

An object of the present invention is to provide a gas chromatograph that can obtain analytical results with few errors even when the sample contains high-boiling point components or requires measurement of low-concentration components.

The present invention is characterized by a normal introduction operation mode in which the injection needle is kept in the sample vaporization section for the time necessary for injecting the sample into the sample vaporization section, and a normal introduction operation mode in which the injection needle is kept in the sample vaporization section for the time necessary for injecting the sample into the sample vaporization section, and an inside of the sample vaporization section during the normal introduction operation mode. A mode selection unit is provided that allows selection of a special introduction operation mode in which the injection needle is kept in the sample vaporization section for a longer time than the retention time in the sample vaporization section, and when the special introduction operation mode is selected, the injection needle is A time changing section is provided to keep the residence time from the introduction operation into the sample vaporization section to the withdrawal operation from the sample vaporization section longer than that in the normal introduction operation mode.

In a preferred embodiment of the present invention, when the special introduction mode is selected, the syringe injects the sample more slowly than in the normal introduction mode while the injection needle remains in the sample vaporizing section. A syringe drive is provided for operation. in particular,
An air cylinder was provided to drive the piston of the syringe, and this air cylinder was provided with a speed control valve to change the speed of movement of the piston.

A normal sample is one that contains almost no high-boiling point components and consists mostly of low-boiling point components, and is injected in a minute amount within the capacity of the sample vaporizer to introduce into the column.
In the gas chromatograph used in the Examples described below, the amount of sample normally injected is, for example, about 10 μm, and the residence time of the injection needle in the sample vaporization section in the normal introduction mode is, for example, 1 second.

For samples that require measurement of low-concentration components, use a large sample volume, e.g. 50μ, to increase the detection peak.
is injected into the sample vaporization section, but if it is injected within 1 second of the retention time as in the conventional case, the introduction capacity of the sample vaporization section into the column will be exceeded, so the sample vaporized all at once will be at a lower temperature than the sample vaporization section. The gas will diffuse back toward the carrier gas supply flow path. Then, the diffused and liquefied sample gradually enters the sample vaporization section as the carrier gas is introduced, and it takes an extremely long time until the entire sample is completely introduced into the column. For example, it takes more than 30 seconds. For this reason, the separation between the components becomes extremely poor as shown in FIG. 3a.

In the present invention, when a large amount of sample is injected because low concentration components need to be measured, the special introduction operation mode is selected. In this case, the time that the injection needle stays in the sample vaporization section is set to, for example, 10 seconds, so that the sample can be vaporized at a speed within the capacity of introduction into the column by slowing down the sample injection operation by the injector. Therefore, it is possible to prevent explosive vaporization of the sample as in the conventional case, and to prevent back diffusion of the sample toward the carrier gas supply channel. As a result,
Although the separation of component peaks is somewhat inferior to that achieved by short-term injection of a small amount of sample, the separation of peaks is much better than that achieved by conventional injection of a large amount of sample.

On the other hand, in the case of a sample containing a large amount of high-boiling point components, if the injection needle remains in the sample vaporizer for about 1 second, as in the conventional case, the liquid sample inevitably remains in the injection needle due to the slow vaporization rate of the sample. The remaining amount of this liquid sample changes each time the injection operation is performed, so
As a result, the amount of sample introduced becomes inaccurate, and highly accurate analysis results cannot be obtained.

The present invention is also effective for samples containing many such high boiling point components. That is, in this case as well, the special introduction operation mode is selected, and the time during which the injection needle remains in the sample vaporization section is set to, for example, 5 seconds. Since the amount of sample to be injected is usually very small, the sample injection operation by the syringe is completed immediately after the injection needle enters the sample vaporization section. After that, the injection needle remains in the sample vaporization section, so even if there is liquid sample remaining inside the injection needle, vaporization will proceed due to the high temperature of the sample vaporization section, and almost all the sample will be completely absorbed into the column within the retention time. will be introduced to Therefore, the amount of sample introduced becomes more accurate than in the past.

FIG. 1 shows a schematic diagram of the vicinity of an autosampler in an embodiment of the present invention.

In FIG. 1, a sampler body 24 having a turntable 25 is installed in a gas chromatograph 23. A syringe 6 having an injection needle 30 is attached near the tip of the arm 9. First, the syringe 6 is positioned directly above a particular sample bottle 22 arranged on the turntable 25 . When the analysis operation starts, the arm 9 is lowered and the injection needle 30 of the syringe is inserted into a particular sample bottle 22 containing a liquid sample. The arm 4 then rises to raise the piston 5 of the syringe 6, causing the syringe 6 to rise.
A liquid sample is aspirated into the tube through the needle 30. After suction and retention of a predetermined amount of the sample is completed, the arm 9 is raised and then moved to a position directly above the drain tray 26. Then, the arm 4 is lowered and the piston 5 is pushed down to discharge the sample in the syringe 6 into the drain pan 26.
The above is the cleaning process.

The arm 9 then moves again directly above the particular sample bottle 22 and lowers the arm 9 to position the syringe needle 3.
0 into the same sample bottle 22. In this state, the arm 4 is moved up and down. This is called a bubble removal process. The bubble removal process removes air bubbles mixed in the sample. Next, arm 4 is raised and stopped,
After aspirating a predetermined amount of sample into the syringe 6, the arm 9 is raised. Next, the arm 9 swings horizontally to just above the injection port 7 of the gas chromatograph 23, and then descends to insert the needle 30 of the syringe 6 into the injection port 7.
The arm 4 is inserted into the sample vaporization section.
The sample is injected into the vaporization section by the descent of the sample.

After injecting the sample, the arm 9 rises and swings horizontally until it is directly above the sample bottle 22, and the turntable 25 rotates to position the next sample directly below the syringe 6 and wait for the start of the next analysis.

FIG. 2 is a diagram illustrating the sample injection operation in the embodiment of FIG. 1. The residence time selection section 35 has an operation panel and a microprocessor 40,
A switch 27 is provided on the operation panel.
Syringe lowering command from microprocessor 40
The valve drive circuit 3 is operated by the CD, and the switching valve 14 is switched to the flow path as shown by the solid line in the figure. Then, air from the driving air inlet 18 is supplied to the air cylinder 8, and the arm 9 is lowered, so that the injection needle 30 of the syringe 6 penetrates the injection port 7 having a rubber septum, and the sample is kept at about 250°C. Vaporization section 32
Inject inside. Air from the air cylinder 8 is exhausted from the exhaust port 20. The needle 30 is the sample vaporizing section 32
The drive circuit 3 operates according to an injection command from the microprocessor 40 while the valve 13 is stopped.
becomes a flow path as shown by the solid line in the figure, and air from the drive air inlet 15 is supplied to the air cylinder 10. Therefore, the arm 4 descends and pushes down the piston 5 of the syringe 6, so that the liquid sample held in the syringe 6 passes through the needle 30 to the sample vaporizer 3.
Injected into 2. Air from the air cylinder 10 is exhausted from the exhaust port 17.

If the needle valve 12, which is the speed control valve on the exhaust side of the air cylinder 10, is throttled in advance,
The piston 5 slowly descends, slowing down the sample injection speed. The syringe raise command CU from the microprocessor 40 is transmitted to the drive circuit 3 via one of the plurality of delay circuits 41 and 42. Selection of the delay circuit is performed by a switch 27 on the operation panel. Injection needle 30 in sample vaporization section 32
The residence time is about 1 second when the delay circuit 41 is selected, and is applied to normal samples. The residence time when the delay circuit 42 is selected is about 5 seconds, and is applied to samples containing high boiling point components or highly viscous samples.

When the residence time has passed, the switching valve 14 switches,
The flow path is indicated by the dotted line in the figure, and the driving air inlet 18 is communicated with the lower side of the air cylinder 8, and the arm 9 is raised. Air from the upper side of the air cylinder 8 is exhausted through the exhaust port 19. As a result, the injection needle 30 is pulled out from the injection port 7.

At the time of the above-mentioned bubble removal step, the needle valve 11, which is a speed control valve on the exhaust path leading from the air cylinder 10 to the exhaust port 16, is throttled, and the rising speed of the piston 5 when the switching valve 13 is in the dotted line flow path is adjusted. Take your time. At the same time, the time that the injection needle 30 remains in the sample bottle 22 during sample inhalation can be maintained for a long time. That is, delay circuit 42 is selected. As a result, the injection needle 30 quickly discharges the sample in the sample bottle 22, and after waiting for a while, the injection needle 30 is immersed in the sample liquid and the sample can be slowly inhaled, allowing for better bubble removal. can be done.

FIG. 3 is a comparison of an example in which the same sample was analyzed using conventional method a and method b to which the present invention is applied.
This is an example of a chromatograph when a large amount of sample is introduced into the vaporization section. In conventional method a, the residence time of the injection needle in the vaporizing section is always 1 second, so the
When a sample of I can't. In method b to which the present invention is applied, the special introduction operation mode is selected, and the residence time of the injection needle 30 in the vaporizing section 32 is set to 10 seconds, during which the piston 5 is slowly lowered by the air cylinder 10. , the same volume (50μ) of liquid sample is completely vaporized. As a result of effective vaporization of the sample, sample components can be separated well.

In the above-described embodiment, a delay circuit changeover switch is provided on the operation panel, but the method for setting the delay time is not limited to this. By inputting conditions in advance into the microcomputer using the numerical keys on the operation panel, the order of samples to be sampled and the residence time corresponding to the sample can be stored, and execution can be performed based on these.

As described above, according to the present invention, analysis results with small errors can be obtained even for samples containing high boiling point components or samples requiring measurement of low concentration components.

[Brief explanation of drawings]

Figure 1 is a schematic external view of an autosampler in an embodiment of the present invention, Figure 2 is an explanatory diagram of sample injection operation in the embodiment of Figure 1, and Figure 3 is a comparison of chromatographs when a large amount of sample is injected. It is a diagram. 5...Piston, 6...Syringe, 8,10...
Air cylinder, 11, 12...Speed control valve, 1
3, 14...Switching valve, 22...Sample bottle, 30...Injection needle, 32...Sample vaporization section, 35
...Residence time selection section.

Claims (1)

[Scope of Claims] 1. In a gas chromatograph in which a liquid sample is aspirated from a sample container into a syringe through an injection needle and is automatically injected by entering the injection needle into the sample vaporization section, a normal introduction operation mode in which the injection needle remains in the sample vaporization section for the time necessary for injection into the sample; A mode selection section is provided that can select a special introduction operation mode in which the injection needle remains in the sample vaporization section, and when the special introduction operation mode is selected, the sample vaporization is performed from the operation of advancing the injection needle into the sample vaporization section. 1. A gas chromatograph, comprising: a time changing section that maintains a residence time until a pulling operation from the section is longer than that in the normal introduction operation mode. 2. In a gas chromatograph that automatically injects a liquid sample sucked from a sample container into a syringe through an injection needle by entering the injection needle into the sample vaporization section, normally the liquid sample required for injecting the sample into the sample vaporization section is A normal introduction operation mode in which the injection needle is kept in the sample vaporization section for an amount of time; A mode selection unit is provided that can select a special introduction operation mode in which the injection needle is stopped in the sample vaporization unit, and when the special introduction operation mode is selected, the injection needle is in the normal introduction operation mode while the injection needle remains in the sample vaporization unit. A gas chromatograph characterized by being provided with an injector drive device that causes the injector to perform a sample injection operation more slowly than the injector.