A study on the stability of low level standard gas (halocarbons) in pressurized cylinders

加压钢瓶中低浓度标准气体（卤代烃）的稳定性研究

• 批准号: 08640628
• 负责人: YOKOUCHI Yoko
• 金额: $ 1.47万
• 依托单位: National Institute for Environmental Studies
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1996
• 资助国家: 日本
• 起止时间: 1996 至 1997
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-08640628/
• 关键词: standard gas; organic halogenated compounds; stability

Stability of 1ppbv standard gases containing methyl chloride, methyl bromide, methyl iodide, trichloroethylene, tetrachloroethylene, carbon tetrachloride, were tested in pressurized cylinders with five types of material ; widely-used Al, widely-used Mn/Fe, 1s (surface roughness<1um) -Al, 1s-Mn/Fe, widely-used Ni-Fe. Significand reduction of methyl bromide and methyl iodide was found in the three canisters other than 1s-Al and 1s-Mn/Fe after a 3-month experiment, suggesting that these two compoounds are unstable on the rough surface. Carbon tetrachloide was significantly reduced in 1s-Mn/Fe cylinder, probably due to its high reactivity with Fe.Stability of 100 pptv standard gases in 1s-Al and 1s-Mn/Fe was also tested using eight cylinders for each. For such low concentration of standards, any of 1s-Al and 1s-Mn/Fe cylinders showed some decrease of methyl bromide and methyl iodide after two-month storage. Furthermore, the reduction rate was not always same even for the same type of cylinders : they ranged from <10% to 99%.These findings suggest that working standard gases containing unstable components (such as methyl iodide) at low concentration should be calibrated with dynamic dilution of 1 ppm standard gases which have been proved to be stable for more than 1 year. Since the reduction rates were found to be linearly related with the time after the preparation of standards, correction factors for each standard gas can be speculated from periodic calibration (-once a month).

用常用的Al、Mn/Fe、1 s-Al、1 s-Mn/Fe、Ni-Fe五种材料，在加压气瓶中对1 ppbv氯甲烷、溴甲烷、碘甲烷、三氯乙烯、四氯乙烯、四氯化碳标准气体的稳定性进行了试验。除1 s-Al和1 s-Mn/Fe外，其它三种样品中溴甲烷和碘甲烷的含量在3个月的实验中均显著降低，表明这两种化合物在粗糙表面上不稳定。1 s-Mn/Fe柱中的四氯化碳被显著降低，这可能是由于其与Fe的高反应性。1 s-Al和1 s-Mn/Fe柱中的100 pptv标准气体的稳定性也分别用8个柱测试。对于如此低浓度的标准品，任何1 s-Al和1 s-Mn/Fe圆柱体在储存两个月后均显示出甲基溴和甲基碘的一些减少。结果表明，对于含碘甲烷等不稳定组分的低浓度工作标准气体，应采用1 ppm标准气体动态稀释法进行标定，且该标准气体已被证明稳定1年以上。由于发现还原率与标准品制备后的时间呈线性关系，因此可以通过定期校准（每月一次）推测每种标准气体的校正因子。