Standard gas distribution method

There are three methods of standard gas distribution:

1. Syringe gas distribution method

When only a small amount of standard gas is required, a 100ML syringe can be used to prepare the standard gas; the required low-concentration standard gas can be obtained after multiple dilutions. The concentration of the standard gas can be calculated according to the concentration of the raw material gas and the dilution factor. The syringe used for gas distribution must have good air tightness, small volume and accurate system. Put a small piece of teflon sheet before gas distribution for stirring.

Although the syringe gas distribution method is simple and easy, the concentration of some standard gases is also very accurate, but due to the influence of factors such as the adsorption on the inner wall of the syringe, the large dead volume and the incomplete volatilization of the liquid, the prepared gas concentration error is large, and many organic The standard gas of the compound should not be prepared by this method. When dispensing gas with volatile liquids, it is especially necessary to use a syringe to dispense gas after passing the verification.

2. Plastic bag gas distribution method

In this method, a plastic bag is used as a container, a certain amount of raw gas is accurately measured with a gas quantitative tube according to the figure, an appropriate amount of diluent gas is drawn into the plastic bag with a syringe through a three-way piston, and the plastic bag is repeatedly squeezed to mix the gas. Calculate the concentration of standard gas in the bag according to the amount of feed gas and diluent gas added.

When using plastic bags for gas distribution, it is necessary to prevent the bag wall from adsorbing gas, the bag wall and the gas reaction and leakage. General plastic bags have obvious adsorption effect on most gases and cannot be used for gas distribution. Usually, PTFE bags, polyester resin plastic bags and polyethylene film aluminum foil sandwich bags are used for gas distribution.

3. High pressure cylinder gas distribution method

This gas distribution method is a method of using a high-pressure steel cylinder as a container to form a mixed gas with a higher pressure, also known as a high-pressure gas distribution method. According to the gas distribution measurement method, the high-pressure cylinder gas distribution method is divided into four types: pressure method, flow method, volume method and mass method. Among them, the concentration of standard gas prepared by the mass method is the most accurate. It is used as the benchmark method for preparing standard gas. Widely used to prepare standard gases such as COCH4 and NO.