Evaluation of dynamic headspace and purge-and-trap techniques for the high-resolution gas chromatography analysis of nitrous oxide in seawater

Abstract

The present study focuses on the effectiveness of dynamic headspace (DH) and purge-and-trap (PT), which are two commonly used techniques for determining volatile organic compounds in environmental samples, on the extraction and trace analysis of nitrous oxide in seawater. With the aim of obtaining reliable quantitative data in the DH and in the PT techniques, kinetics of these processes were studied; a first-order kinetic-like function is found to be followed for the extraction of nitrous oxide in both the DH and PT sampling methods. A three-way analysis of variance was carried out to evaluate the effect of the water sample composition on DH and PT analysis in order to systematically and accurately examine the effect of different factors on the chromatographic response of N 2O; a significant matrix effect proportional to the nitrous oxide concentration was observed when bidistilled water, synthetic and natural seawater were considered. The effects of different sampling procedures were evaluated in terms of linearity range, limit of detection, capability of detection, precision, extraction recovery and accuracy. Better results in terms of extraction recovery, sensitivity and detection limit were obtained when applying the purge-and-trap technique combined with GC–electron-capture detection; detection limits at very low pmol ml −1 levels were achieved, making this procedure suitable for trace nitrous oxide analysis in marine samples.