Nitrogen dioxide standard gas is unstable.

1, cylinder surface treatment. The surface of gas cylinder must be clean and dry, and collision should be avoided in the preparation process to avoid quality change and affect weighing accuracy.

2. Treatment of gas distribution system. Regularly check the cleanliness and tightness of the gas distribution system, especially the gasket and connecting parts of the vacuum pump filter should be replaced regularly. Before the system is inflated, the pipeline should be emptied or purged, and it should be cleaned alternately by pressurization and decompression. When filling, the pressure of filling gas should always be higher than the pressure in the bottle to prevent diffusion.

3. Uncertainty of weight in the atmosphere. Weighing in the atmosphere, ambient temperature, atmospheric pressure, air relative humidity and the increase of cylinder volume during filling will bring uncertainty. These uncertainties caused by ambient temperature, atmospheric pressure and humidity are accurately measured and corrected by formulas.

4. Uncertainty of balance weight value. The weights used in standard gas weighing should be checked and calibrated regularly.

5. Uncertainty caused by disassembly and assembly of gas cylinders. According to the number of parts prepared and the number of disassembly times, the quality of the gas cylinder will change after multiple disassembly, but the experiment proves that the change brought by the disassembly of the gas cylinder can be ignored as long as it is carefully disassembled.

6. Uncertainty of purity analysis of feed gas. The standard gas is a mixture of raw gas and diluent gas. From the method of weight concentration calculation formula, it can be seen that the purity of raw gas is directly related to the accuracy of standard gas value, especially the content of related gases in dilution gas will directly affect the content of superimposed standard gas.