The use of reverse diffusion to validate the performance of diffusive samplers.
A number of different protocols have been put forth for measuring reverse diffusion from diffusive samplers. The basic concept is that reverse diffusion tests, depending as they do on basic laws of mass transfer, are not independent of one another, but may give general information about the limits to the possible change that can occur if the conditions to measure reverse diffusion are changed. Laboratory measurements of the reverse diffusion of vinyl chloride, using 3M and SKC diffusive samplers, following both the National Institute for Occupational Safety and Health (NIOSH) and the European Union test protocols, support the mathematical analysis developed in this article. An important conclusion is that if in following the NIOSH protocol a diffusive sampler loses 10% of its analyte over a period of 4 hours, then the maximum loss expected from a sampler allowed to back-diffuse for 8 hours is 19%.