A new method is described that facilitates determining the efficiency of air sampling traps to adsorb and thermally desorb volatile organic compounds. A known volume of a liquid standard of volatile organic compounds is vaporized into an air stream, a fraction of which is collected on an air sampling trap. This trap is subsequently thermally desorbed and analyzed using a GC/FID. The efficiency of the trap to adsorb and thermally desorb each compound tested is calculated.