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

1997 Fiscal Year Final Research Report Summary

• Project/Area Number: 08640628
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: 地球化学
• Research Institution: National Institute for Environmental Studies
• Principal Investigator: YOKOUCHI Yoko National Institute for Environmental Studies, Division of Environmental Chemistry, Senior Research Scientist, 化学環境部, 主任研究員 (20125230)
• Co-Investigator(Kenkyū-buntansha): AKAMA Isamu Taiyo Toyo Sanso Co., Ltd., Research Scientist, 特殊ガス本部, 研究員
• Project Period (FY): 1996 – 1997
• Keywords: standard gas / organic halogenated compounds / stability

Research Abstract

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).