A transfer technique of small amount of gas for the preparation of standard gas mixtures

Standard gas mixtures (SGMs) of trace level in high-pressure cylinder are typically prepared by multi-stage dilution from the pure gases. Here ‘a small amount of gas transfer technique’ was developed to prepare SGMs, in which the number of dilution stages could be much less than typical process. The preparation process and the technique were introduced in detail. And the theory and key points of the technique were discussed. As an example, Freon 12 SGMs of trace level (100 nmol/mol) were prepared by the technique through only three-stage dilution, the relative standard uncertainty of preparation was less than 0.2%. The results showed consistency agreement of <0.2%. In order to verify the reliability of the technique a Freon 12 SGMs of 1 μmol/mol and 0.1 μmol/mol were prepared by conventional method through four-stage and five-stage dilution respectively. The standard uncertainty of Freon 12 prepared by two methods was similar and the result of the consistency of two methods was satisfied. Considering the savings of time and labor, the technique is worth to be recommended.

► Report a novel technique to prepare standard gas mixtures in detail for the first time.
► Design a new system to prepare gas mixtures according to this new technique.
► By using novel technique, only three-stage dilution is needed to prepare R12/N2 of 0.1 μmol/mol from pure gases.
► This novel technique is very useful to prepare low concentration standard gas mixtures.