Comparing Headspace With Purge and Trap for Analysis of Volatile Priority Pollutants

Headspace sampling is compared with purge-and-trap techniques for the gas chromatographic (GC) analysis of volatile pollutants in water. An objective comparison of the two sample introduction techniques was made by using the same GC, column, and detectors for identical analyses run first by purge and trap and then by headspace. Using optimized headspace conditions described in this article, this technique was as sensitive as the US Environmental Protection Agency purge-and-trap methods for the analysis of volatile pollutants in water. The precision for 24 sequential headspace injections was better than that for purge-and-trap analyses. The relative advantages and disadvantages for these two sampling methods are also discussed. Purge-and-trap sampling is routinely used for the analysis of volatile priority pollutants in water because the tech- nique is recommended by the US Environ- mental Protection Agency (USEPA).1-4 In this procedure, a 5-mL water sample is placed in a purge vessel. The sample is then sparged with carrier gas for several minutes to remove volatiles, which are trapped on a solid adsorbent. Ballistic heating of the trap desorbs the volatiles, which are carried to the gas chromato- graph (GC) injection port in the carrier- gas stream. Headspace sampling has been widely used for the analysis of volatiles in virtually any matrix5 and has often been applied to environmental samples such