Adsorption isotherms for compounds of moderate and low volatility are difficult to measure as the Henry's law region is approached. A novel experimental technique has been developed that can measure ultra-low concentration adsorption equilibrium. This new technique requires pre-equilibration of adsorbable components with adsorbents, and then employs purge-and-trap chromatographic methods to measure the ultra-low equilibration concentrations. Preparation of the samples and the analysis method will be discussed. The results will be compared with adsorption theories.