SPME of 52 pesticides and polychlorinated biphenyls: Extraction efficiencies of the SPME coatings poly(dimethylsiloxane), polyacrylate, poly(dimethylsiloxane)-divinylbenzene, carboxen-poly(dimethylsiloxane), and carbowax-divinylbenzene

Fiber/water partition coefficients (K-fw) of 52 pesticides, including triaz ines, organophosphorus pesticides, organochlorine pesticides, and polychlor inated biphenyls (PCBs) were experimentally calculated for the five polymer ic coatings poly(dimethylsiloxane) (PDMS), polyacrylate (PA), poly(dimethyl siloxane)-divinylbenzene (PDMS-DVB), Carboxen-poly(dimethylsiloxane) (CAR-P DMS), and Carbowax-divinylbenzene (CW-DVB) commercially available for solid -phase microextraction coupled to gas chromatography, The equilibrium-time profiles for the five coatings were previously studied in order to establis h the time needed for equilibrium, To calculate K-fw, the amount of analyte extracted at equilibrium was obtained by gas chromatographic analysis of s piked water samples. In the case of mixed coatings in which adsorption proc esses are involved the term partition coefficient is not strictly correct a nd partition coefficient apparent is used in these cases. For the triazines , small partition coefficients were found, showing that PDMS-DVB permits th e best extraction for these compounds. PA and PDMS-DVB gave the highest mea n partition coefficients for the organophosphorus pesticides. Organochlorin e pesticides in general gave high K-fw with all five coatings, with strong differences depending on the compound. In the case of PCBs a decrease in th e partition coefficient with the increase of the number of chlorines substi tuted was observed. The results obtained indicated that the polarity of the fibers is not the main factor affecting the extraction. The presence of DV B in the mixed coatings seems to increase the uptake, probably due to adsor ption processes instead of absorption. In general the PDMS-DVB coating prov ed to be a good choice for the analysis of the compounds under study.