Abstract: A diffusive sampler comprises a housing with an opening and containing a sorbent, preferably having a barrier between the sorbent and the opening to prevent convection currents but still allowing the exchange of the analyte and the sorbate(s) by diffusion, and at least one sorbate carried by the sorbent. The sorbates will be desorbed when the sampler is exposed to the fluid to provide a check on the apparent duration of the exposure and a correction to the calculation of analyte concentration in the fluid that results from desorption and reverse diffusion. The barrier may be either a fluid-permeable matrix or a fluid gap with a thin, fluid-permeable membrane for blocking convection currents but otherwise admitting fluid and analyte.