where: t = length of sampling period (min)
K = uptake constant (cm3 toluene/min).
NOTE: The uptake constant must be known accurately (either be supplied by the sampler manufacturer or determined by the user by calibration with standard toluene-in-air mixtures [5]). K can be estimated from the diffusion coefficient, D (c2m/min), the cross-sectional area, A (cm2), and the diffusion pathlength, L (cm), of the sampler: