A process is provided for determining the amount of sulfuryl fluoride in the atmosphere of an enclosed area that has been fumigated with sulfuryl fluoride (SO 2 F 2 ). This process comprises: (A) sampling said atmosphere of said enclosed area to obtain a gaseous sample; (B) selectively removing water from said gaseous sample by passing said gaseous sample through a perevaporation zone to obtain a perevaporated sample, wherein said perevaporation zone comprises a copolymer of tetrafluoroethylene and perfluoro-3,6-dioxa-4-methyl-7-octene-sulfonic acid; and (C) analyzing said perevaporated sample in a sulfuryl fluoride detector to determine the amount of sulfuryl fluoride in said perevaporated sample.