Application and preparation technology of standard gas

 Standard gas is an industrial term for gas, and standard gas belongs to standard substances. Reference materials are highly homogeneous, well-stabilized and quantitatively accurate determination standards. They have the basic function of reproducing, preserving and transmitting quantitative values. They are used in the fields of physical, chemical, biological and engineering measurement to calibrate measuring instruments and measuring processes. , evaluate the accuracy of the measurement method and the testing ability of the testing laboratory, determine the characteristic value of the material or product, and conduct quantitative arbitration, etc.

      Whether it is laboratory chromatographic analysis or calibration of online analytical instruments, a large amount of high-quality standard gas is required to accurately calculate the content of components in products. Therefore, standard gases have been widely used in product quality supervision and quality control, instrument calibration, atmospheric environment monitoring, medical and health care, clinical testing, and evaluation of analytical methods. In recent years, the petrochemical industry has developed rapidly. When using petroleum as raw material to produce polymer-grade ethylene, propylene, hydrogen, benzene, and p-xylene, the analysis of product composition is realized by chromatographic analysis.

1. Preparation of standard gas mixture

      The standard mixed gas is prepared by using a high-purity gas as a diluent gas and adding one or several other high-purity gases. The preparation methods of standard gas mainly include weighing method, partial pressure method, volume method, permeation method, saturation method, electrolysis method, exponential dilution method, flow ratio mixing method, etc. Dynamic gas distribution. The static gas distribution method is to return a certain amount of gaseous or vaporous raw material gas into a container of known volume, then fill it with diluent gas, and mix it uniformly.

2. Preparation method of single component

      The methods for preparing single-component standard gases vary according to the properties of the substances. For liquid substances with strong volatility, they can be prepared by their volatilization effect, and those that cannot be prepared by volatilization method can be prepared by chemical reaction method.

Technology for Standard Mixed Gas Preparation

1. Pressure ratio method: In this method, when the mixed gas is prepared, the gas is distributed according to the specified concentration according to the pressure of each component.

2. Static volume method: At present, the national standard still uses the static volume method for the gas distribution of the gas distribution device.

3. Gravimetric method: This method uses a high-load precision balance to weigh each gas component in the cylinder, and calculates the concentration of the standard gas in the cylinder according to the mass ratio of each component.

4. Permeation tube method: The permeation tube is a kind of equipment that provides the raw material gas source, which is mainly composed of a small container for the raw material liquid and a permeable membrane.

5. Mass flow ratio method: This method uses the method of flow ratio mixing to prepare the standard gas, so the accurate measurement of the flow rate is the key to ensure the preparation.