22种氯代烃标准气体的瓶内均匀性研究

Within-bottle Homogeneity Study of 22 Chlorinated Hydrocarbon Gas Standards

分子量大的氯代烃在气瓶内可能出现分层、沸点高的氯代烃可能在气瓶内吸附,从而引起挥发性氯代烃混合标准气体出现瓶内不均匀的现象。研究确定了氮气中22种挥发性氯代烃标准气体瓶内均匀性的实验方法,并通过考察量值随样品压力的变化来评价样品在瓶内的均匀性。根据实验结果分别计算了22种氯代烃瓶内不均匀性所引起的不确定度,结果显示在样品压力<2 MPa时,1,1,2,2-四氯乙烷、间二氯苯、对二氯苯、邻二氯苯的量值显著变大,其瓶内不均匀性所引起的不确定度>2%。样品压力<2 MPa,22种挥发性氯代烃标准气体会出现不均匀现象,因此样品的最低使用压力为2 MPa。

Chlorinated hydrocarbons with high molecular weight can stratify in the gas cylinder, and chlorinated hydrocarbons with high boiling point can be adsorbed in cylinders, which resulted in inhomogeneous value of gas standard. The experimental method of within-bottle homogeneity of 22 chlorinated hydrocarbon gas standards was established, and whether the trend for the values varying with the sample pressure changed was used to investigate the sample homogeneity. Based on results, uncertainty of inhomogeneity was calculated. When sample pressure is lower than 2 MPa, values of 1,1,2,2-four ethylene oxide,p-dichlorobenzene,p-dichlorobenzene,o-dichlorobenzene significantly became larger, and uncertainty of inhomogeneity is bigger than 2% Sample pressure lower than 2 MPa, 22 volatile ohlorinated hydrocarbons standard gas will became inhomogeneous, so the minimum pressure was determined at 2 MPa.