USE OF SEQUENTIAL PURGING WITH THE STATIC HEADSPACE METHOD TO QUANTIFY GASOLINE CONTAMINATION

The static headspace method used with portable gas chromatographs has become an important means of field screening environmental samples for gasoline contamination. A major limitation in using this method is the simultaneous detection (coelution) of other volatile gasoline constituents with those of interest. This is particularly problematic in the quantitation of methyl-t-butyl ether (MTBE), benzene and toluene. A sequential purging technique was used with static headspace analysis to remove coeluting compounds and to improve the accuracy in the quantitation of MTBE and aromatic constituents. Aqueous constituent concentrations determined using sequential purging were generally within 20% of those determined from laboratory purge and trap/gas chromatography (EPA method SW 846-602) analyses, Without sequential purging, constituent concentrations determined using the static headspace method were found to be 2 to over 10 times that of laboratory analyses. Further, in very contaminated samples, sequential purging permitted quantitation of constituents which were not resolvable in the initial headspace analysis due to coelution.