Quantitative evaluation of a simple dynamic headspace analysis technique for non-polar pollutants in aqueous samples at the ng/kg level
✍ Scribed by W.E. Hammers; H.F.P.M. Bosman
- Publisher
- Elsevier Science
- Year
- 1986
- Tongue
- English
- Weight
- 552 KB
- Volume
- 360
- Category
- Article
- ISSN
- 1873-3778
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✦ Synopsis
The theoretical and practical aspects of the various modes of headspace analysis have been reviewed by Drozd and Novak' and, more recently, by Nufiez et al. '.
In this paper we report some quantitative data obtained with the purge-and-trap technique. The aqueous sample solution is purged with pure nitrogen. The analytes are collected in a Tenax trap. The trap tube is mounted to the injection port of a gas chromatograph. The analytes are thermally desorbed, and concentrated as a narrow band at the top of a capillary column that is cooled with liquid nitrogen. Thereafter, the analytes are separated and detected with a flame ionization detector. This simple off-line mode has been described by several workers3p4, and is attractive because of its low costs and applicability to any modem gas chromatograph. Since quantitative results (recovery and repeatability data) are rather scarce and, as far as we know, not yet given at the ng/kg level, we carefully examined each of the above-mentioned procedure steps for a number of alkanes, alkylbenzenes and some chlorinated ethenes. To this aim, we analysed distilled water, natural ditch water, and a soil-water suspension spiked with known amounts of these solutes. Recovery data, larger than theoretically predicted, will be explained. It will be shown that quantitation at the ng/kg level includes the proper choice of a reference compound and internal Stan: dards, and the elimination of carry-over effects due to incomplete desorption of the analytes and due to a slight deterioration of Tenax TA. Finally, the possibilities and the limitations of this type of purge-and-trap method will be discussed.
EXPERIMENTAL
Chemicals, standard and sample solutions, gas pur$cation, and trap adsorbent
n-Alkane, benzene and alkylbenzene standards were supplied by Chrompack (Middelburg, The Netherlands), and the chlorinated ethenes by Merck (Darmstadt, F.R.G.). Stock solutions of these standards in methanol were stored at -2o"C, and had a shelf-life of at least one month. The spike solutions prepared from the stock solutions, were used within two days. The most volatile standards (heptane and the