Dynamic Headspace Technique Purge and Trap

An analytically interesting variant of the procedure is the fine dispersion of liquid samples in to a carrier gas stream. This so-called spray and trap process uses the high surface area of the sample droplets for an effective gas extraction. The procedure also works very well with foaming samples. A detergent content of up to 0.1% does not affect the extraction result. The spray and trap process is therefore particularly suitable for use with mobile GC-MS analyses (Matz 1993). 

A P T analysis procedure consists of three main steps  

The purge efficiency is defined as that quantity of the analytes, which is purged from a sample with a defined quantity of gas. It depends upon various factors. Among them are purge volume, sample temperature and nature of the sparger (needle or frit), the nature of the substances to be analysed and that of the matrix. 

The purge efficiency has a direct effect on the percentage recovery (the quantity of analyte reaching the detector). 

Control of Purge Gas Pressure during the Purge Phase 

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The dynamic headspace technique (purge and trap) comprises the continuous extraction of volatile compounds from the matrix into the gas phase followed by a concentration step. The transfer of volatile compounds into the gas phase is limited mainly by their volatility. Although this enables volatile substances to be distinguished from less volatile ones, there is no way of differentiating between substance classes of volatiles during the purge step. 

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