RETENTION MODEL FOR SORPTIVE EXTRACTION THERMAL-DESORPTION OF AQUEOUSSAMPLES - APPLICATION TO THE AUTOMATED-ANALYSIS OF PESTICIDES AND POLYAROMATIC HYDROCARBONS IN WATER SAMPLES

In this report, an automated method for sorptive enrichment of aqueous samples is presented. It is based on sorption of the analytes of inte rest into a packed bed containing 100% polydimethylsiloxane (PDMS) par ticles followed by thermal desorption for complete transfer of the enr iched solutes onto the GC column. Compared to other solvent-less sampl e preparation techniques for water samples, several improvements can b e noted of which the most obvious are an enhanced sensitivity and impr oved blanks. Moreover, degradation products formed from the PDMS mater ial can easily be identified with the use of a mass spectrometric dete ctor. As these products contain silicone, they do not interfere with t he target solutes (pesticides, PAHs). In this report a theory model is derived which allows calculation of breakthrough volumes from octanol -water partitioning coefficients (K-O/W). Alternatively, the K-O/W val ue required for complete retention can be calculated using only the sa mple volume and trap specific parameters. For a sample volume of 10 ml , theory predicts a required log K-O/W of 1.77 for the trap used here which was found to be in good agreement with experimental results. For the most apolar solutes, with a log K-O/W in excess of seven, poor re coveries were found. This is most likely due to adsorption of these ap olar solutes in the system. With the current set-up, detection limits are in the order of 10 ng/l using mass spectrometric detection in the full scan mode. (C) 1998 Elsevier Science B.V.