Solid-phase microextraction and gas chromatography-mass spectrometry for analysis of phenols and nitrophenols in rainwater, as their t-butyldimethylsilyl derivatives

Solid-phase microextraction (SPME) coupled with gas chromatography-mass spectrometry has been used for analysis of four phenols and sixteen nitrophenols in rainwater samples. Analytes were extracted from the water in the immersion mode and derivatised for 5 min during direct desorption in the GC injector. Before desorption, 2 mu L N-(t-butyldimethylsilyl)-N-methyltrifluoroacetamide (MDBSTFA) was introduced into the injector, which was maintained at 280 degrees C. Different conditions affecting extraction efficiency were studied, including temperature, type of microextraction fibre, and effect of pH and ionic strength. Five different fibre coatings were tested: 85-mu m polyacrylate (PA), 100-mu m polydimethylsiloxane (PDMS), 65-mu m Carbowax-divinylbenzene (CW-DVB), 75-mu m Carboxen-polydimethylsiloxane (CAR-PDMS), and 65-mu m polydimethylsiloxane-divinylbenzene (PDMS-DVB). The best conditions were use of PA fibres for 40 min at ambient temperature (75 g NaCl per 100 mL, pH 3.0). MDBSTFA was used as derivatising agent because it enables analysis of phenols derivatives with high confidence in identification, because in electron-impact mode TBDMS-phenol derivatives produce the specific M-57 ion. Quantification was achieved by using 4-nitrophenol-d4, at 1 mg L-1, as internal standard. Linearity was good, with correlation coefficients in the range 0.9888 (o-cresol) to 0.9987 (dinitro-o-cresol, DNOC). Detection limits varied between 0.208 and 99.3 mu g L-1 and quantification limits between 0.693 and 331 mu g L-1. Uncertainties varied between 8.7% (phenol) and 17.9% (4-methyl-2-nitrophenol). The method was successfully applied to the analysis of rainwater collected at urban and rural sites in Alsace (East of France). Because of derivatisation in the injector and the associated high temperature, the lifetime of the fibre is severely reduced.