Determination method for methyl iodide using diffusive sampler and capillary GC with thermal desorption injector and FID.

A determination method for methyl iodide in the work place has been developed, using a diffusive sampler and a capillary gas chromatograph with a thermal desorption cold trap injector and an FID. The sampler consists of a glass tube (6 mm o.d., 4 mm i.d., 16 cm length) packed with porous polymer beads. The diffusion path of the sampler is made of a 3 mm i.d., 52 mm length poly (tetrafluoroethylene) tube inserted in the glass tube. The sampling rate of the sampler for methyl iodide was 4.6 ml/h, and variations caused by temperature, relative humidity, and wind speed were found to be small and negligible. The sample could be stored for at least two weeks without significant loss. A time-weighted average concentration of methyl iodide in the range of sub ppm to ppm for two to six hours can be measured by this method. The average concentration of methyl iodide for a period of a few seconds can also be measured by grab sampling, i.e., injecting 20 ml of air directly into the sampler.