Application of the loop method to the preparation of gas reference material

High-accuracy gas reference material is an important prerequisite to guaranteeing the accuracy of stoichiometry. At present, however, the existing procedures of preparing gas reference material are complicated and time-consuming with high degree of uncertainty, so it is difficult to realize the high-accuracy measurement of gas compositions. In this paper, a loop method of preparing the gas reference material was developed. Then, its uncertainty degree on trace materials and preparation process was assessed and compared with the preparation process of the traditional dilution method. Finally, its weighing value was verified by means of a gas chromatography. And the following research results were obtained. First, the weighing cylinder of traditional preparation methods need a balance of wide range and low precision, so the uncertainty degree in the weighing process is introduced many times by multi-stage dilution. Second, when the loop method is adopted to prepare mixed gas reference material, the preparation can be completed in one step, so the uncertainty degree introduced in the preparation process is decreased by one order of magnitude. Third, by virtue of the loop method, the previously-used preparation procedures are simplified, the consumption of raw material is reduced and the preparation efficiency of mixed gas reference material is increased. Fourth, the loop method has been successfully applied to the preparation of gas reference material of natural gas and sulfide mixtures, and it is promising in more extensive application to realize efficient preparation and accurate valuing of gas reference material. And fifth, a gas chromatography is used to verify the nominal value of mixed gas reference material prepared by the loop method. And it is indicated that the loop method is of strong feasibility and accuracy. Keywords: Gas reference material, Stoichiometry, Multi-stage dilution, Loop, High-accuracy, Weighing, Uncertainty assessment