A comparison of gas- and liquid-loaded sorbent standards for the calibration of measurements of volatile organic compounds

The monitoring of volatile organic compounds (VOCs) at environmental levels is commonly carried out in the field using Perkin-Elmer-type sorbent-based passive or active samplers. Measurements of important trace species, such as benzene, toluene and xylenes, are often calibrated using thermal desorption standards that are liquid loaded onto the sorbent. This method is normally adopted over the method of gas loading of standards, on the grounds of ease of application and cost. We report a comparison between sorbent standards prepared by both methods using the sorbent Carbopack X and show that under the conditions used here the two show good agreement with each other. We also present work using liquid-loaded standards on the sorbents Tenax and Chromosorb-106, prepared with the solvents cyclohexane and methanol. The results indicate that, to obtain 100% recovery of the determinands from the desorbed samplers, issues such as type of solvent and sorbent combination together with purge flow should be considered.