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Why Purge & Trap
Purge-and-trap is the ideal method for extracting and concentrating volatile organic compounds (VOCs) from liquids & solids for analysis by GC or GC/MS. The US EPA specifies environmental methods utilizing purge-and-trap for the analysis of VOCs from soil, sediment (SW-846 method 8260), and water samples EPA methods 524 and 624). The technique can also be used to extract VOCs from foods and beverages.
This procedure is particularly useful for concentrating VOCs that are insoluble or poorly soluble in water and have boiling points less than 200°C. The purge-and-trap procedure involves purging a sample with an inert gas, such as nitrogen or helium at ambient temperature (water) or slightly elevated temperatures (soil). This liberates the VOCs, which are efficiently transferred from the aqueous (or solid) phase to the vapor phase. During this purge step, the inert gas is swept to an analytical trap containing a solid sorbent which retain the VOCs. The trap is then desorbed and the VOCs are transferred to the GC for analysis.