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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。
Chlorocarbons with large molecular weight may delaminate in the cylinders. Chlorinated hydrocarbons with high boiling points may adsorb in the cylinders, which may lead to in-bottle unevenness in the standard mixture of volatile chlorinated hydrocarbons. The experimental method for determining the in-bottle homogeneity of 22 volatile chlorinated hydrocarbon standard gases in nitrogen was studied. The uniformity of the sample in the bottle was evaluated by examining the change of the value with the sample pressure. According to the experimental results, the uncertainty caused by the inhomogeneities of 22 kinds of chlorinated hydrocarbon bottles were calculated. The results show that 1,1,2,2-tetrachloroethane, m-dichlorobenzene , P-dichlorobenzene, o-dichlorobenzene significantly increased the value of its in-bottle non-uniformity caused by the uncertainty> 2%. Sample pressure <2 MPa, 22 kinds of volatile chlorinated hydrocarbon standard gas will appear uneven phenomenon, so the sample of the minimum operating pressure of 2 MPa.