JPS628528Y2 - - Google Patents

Description

[Detailed explanation of the invention] This invention uses a carrier gas to separate a certain amount of sample collected by a sampling valve (column) installed away from the sampling valve.
The present invention relates to a collection sample transfer conduit for a gas chromatograph for transfer to a detection section.

FIG. 1 shows a typical configuration example of a gas chromatograph. The sample S is flowed through a sampling valve 1 and a measuring tube 1a attached to the sampling valve 1,
When the sampling valve 1 is switched, a fixed amount (for example, 1 ml) of the sample collected in the measuring tube 1a is transferred by the carrier gas C through the conduit 5 to the separation section (column) 2, where the sample is separated into each component. The amount of each component is sequentially detected by a detection unit, for example, a thermal conductivity type detector 3.

In order to install the sampling valve 1 away from the separation section 2 and near the sample outlet, as shown in FIG. Store 1. This is known as a so-called remote sampling method. In this system, a certain amount of sample is collected by a sampling valve 1 and sent by a carrier gas C through a conduit 5 to a separating section 2 and a detecting section 3 housed in a constant temperature bath 4. The conduit 5 is usually a thin tube made of stainless steel,
For example, one with an outer diameter of 2 mm and an inner diameter of 1 mm is used. The length of this conduit 5 typically amounts to 10 to 30 m.

When measuring adsorbent components such as moisture in a sample using this remote sampling method,
Moisture is adsorbed on the inner wall of the stainless steel tube that is the conduit 5, which widens the width of the moisture peak and degrades peak measurement accuracy. In addition, the degree of moisture adsorption on the inner wall of the stainless steel tube that serves as the conduit 5 is significantly affected by the temperature of the tube, so unless the tube temperature is precisely controlled to a constant value with an accuracy of, for example, ±0.1℃, the moisture peak Outflow time (retention time) is unstable. Incidentally, the stainless steel pipe portion that serves as the conduit 5 is normally heated and kept warm with steam, but the temperature fluctuation range is thought to be 20°C or more.

On the other hand, in order to prevent moisture from being adsorbed to the conduit 5,
It is known to use a tube of non-adsorptive resin such as tetrafluoroethylene or hexafluoropropylene as the conduit 5. However, this resin tube has a property that allows gas to permeate through the tube wall, so if the conduit 5 is long and has a large surface area, the air in contact with the outer wall of the tube will penetrate into the tube.
Mixed with carrier gas. As a result, the measurement sensitivity changes and the detection output baseline fluctuates depending on the amount of air mixed in.

The purpose of this invention is to provide a collection sample transfer conduit that makes it possible to accurately measure the components to be detected.

According to this invention, the transfer conduit is a double pipe, and the inner conduit is made of a resin material that does not easily react with or adsorb the component to be measured in the sample. On the other hand, the external conduit is made of metal or the same type of resin material as the internal conduit. The pressure between the internal conduit and the external conduit is reduced to a pressure lower than atmospheric pressure by a pressure reducing means.

FIG. 3 shows an embodiment of the collected sample transfer conduit according to this invention, in which parts corresponding to those in FIG. 2 are given the same reference numerals. In this invention, the conduit 5 is an internal conduit, and an external conduit is coaxially provided on the outside thereof to form a double conduit. The internal conduit 5 is made of a resin material that does not easily react with or adsorb the component to be detected in the sample, such as a fluorine-based resin such as tetrafluoroethylene or hexafluoropolypropylene, or a chemical material such as polyethylene or polypropylene. Constructed from a physically inert resin. The external conduit 6 may be made of a metal such as stainless steel or copper, or the same type of resin as the internal conduit 5, or any other material, but in general, the transfer conduit needs to be protected by heat, so A heat-resistant material that can withstand temperature is used.

The space between the inner conduit 5 and the outer conduit 6 is evacuated to a pressure lower than the external atmospheric pressure. External conduit 6
One end, for example, the end on the separation section 2 side, is closed with a sealing member 7, and the other end, in this example, the end on the sampling valve 1 side, is connected to a pressure reducing device 8. The pressure reducing device 8 is an aspirator, a pump, or the like, and discharges the gas in the space between the conduits 5 and 6 to the outside, reducing the pressure to at least below atmospheric pressure.

According to this configuration, when measuring moisture in a sample, the collected sample hardly reacts or adsorbs with the conduit 5 when it is sent through the internal conduit 5, so the shape of the detected moisture peak peak measurements can be made correctly without being disturbed. Furthermore, since the pressure between the conduits 5 and 6 is lower than atmospheric pressure, the pressure of the air that is in direct contact with the outer periphery of the conduit 5 is lower than atmospheric pressure, and this air penetrates the wall of the conduit 5 and enters the inside of the conduit 5. The amount entering the conduit 5 is smaller than when the conduit 5 is in direct contact with the outside air, and if the pressure is sufficiently reduced, the amount that penetrates the wall of the conduit 5 and mixed into the carrier gas can be reduced to a negligible level, and the purity of the carrier gas can be reduced. It is possible to prevent changes in the sensitivity of the detected component and fluctuations in the baseline due to changes in the detection component, and the measurement accuracy can be increased accordingly. Note that this invention can be applied not only to detecting moisture but also to detecting hydrogen sulfide, ammonia, and other components.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the general configuration of a conventional gas chromatograph, Figure 2 is a diagram showing the configuration of a conventional remote sampling type gas chromatograph, and Figure 3 is an example of a sample transfer conduit based on this invention. 1 is a diagram showing the configuration of a remote sampling type gas chromatograph. 1: Sampling valve, 2: Separation section, 3: Detection section, 4, 4a: Constant temperature chamber, 5: Internal conduit, 6: External conduit, 7: Sealing device, 8: Pressure reducing device.

Claims (1)

[Scope of utility model registration request] A conduit that transports a certain amount of sample collected by a sampling valve to a separation detection section using a carrier gas. A collection sample transfer conduit for a gas chromatograph, comprising a conduit, an external conduit provided to accommodate the internal conduit, and means for reducing the pressure between the internal conduit and the external conduit to a pressure lower than atmospheric pressure.