The use of silica gel as a component of the sorbent column trap for the determination of volatile organics by GC/MS (SW-846 Method 8240) has been found to lead to water vapor buildup in the instrument vacuum system which results in loss of sensitivity, inaccuracies in the data and in some cases automatic shutdown of the MS due to excess pressure in the ion source.
Several alternative sorbent trap packings have been investigated as a means of alleviating the detrimental effects resulting from the retention of excess water vapor in the GC/MS system. The most successful combinations have excluded silica gel as a sorbent column component.
Instrument response data were generated for the volatile organic target compounds listed on the USEPA Contract Laboratory Program (CLP) and several gaseous Freons using sorbent traps with and without silica gel. Method detection limits were experimentally determined on each trapping system and evaluated for statistically significant differences. Statistical comparisons of trapping efficiency were also performed for the two systems. The method calibration requirements (SPCC and CCC) were evaluated against the method criteria for the silica gelfree sorbent column.
Statistically significant deviations in silica gel-free trap performance were minor and did not adversely affect the achievement of the method performance criteria for SW-846 Method 8240.