Possibilities and limitations of dynamic headspace sampling as a pre-concentration technique for trace analysis of organics by capillary gas chromatography

The possibilities, the limitations and the quantitative performance of dynamic headspace sampling, in particular closed-loop stripping, were investigated for various classes of organic substances in aqueous samples with concentrations down to the parts per 1012 (ppt) level. The effects of variations of some process factors (e.g., the gas-liquid distribution coefficient, the sample temperature, the stripping gas volume and the type of solvent) on the recovery were studied. The experimental results of this study agree fairly well with those predicted by a theoretical model. The recovery is shown to be independent of concentration in a wide range of concentrations (200 ppt-20 ppb). For components that do not interact strongly with water, overall recoveries corresponding to a standard deviation of 10-15% are found. A detection limit of 10 ppt and enrichment factors up to 5000 can easily be obtained for non-polar components with boiling points up to 350°C for a 1-1 sample