A thermodynamic treatment of passive monitors

Previous mathematical descriptions of sampling using passive monitors have used Fick's First Law of diffusion and the assumption that the concentration of adsorbate in the vapor phase above the sorbent is zero. This paper shows that by introducing a simplified expression for the equilibrium vapor pressure, behavior more nearly resembling that observed for passive monitors is predicted. The theory can also be applied to the case of loss of sample from a diffusive monitor. Experimental evidence is also provided which demonstrates that the theory adequately describes the observed results.