Screening for transformation products of pesticides using tandem mass spectrometric scan modes

The applicability of tandem mass spectrometric (MS–MS) scan modes such as constant neutral-loss and precursor-ion scanning to screen for unknown transformation products (TPs) of pesticides at environmentally relevant concentrations (low-μg/l level) is studied. The selection of the MS–MS scan modes is based on the product-ion scan of the parent pesticide, and TPs are detected which are unaltered in the part of the structure concerned. The screening approach is applied to a surface water sample spiked with atrazine and three known TPs at a level of 3 μg/l to study the possibility to extract the TPs from the total ion chromatogram. Next, the approach is used to identify unknown TPs formed after (bio)degradation of two test compounds, fenchlorazole-ethyl (FCE) and furathiocarb (FTC). By using the precursor-ion scan mode, two TPs were detected after biodegradation of FCE, fenchlorazole-methyl and fenchlorazole; in surface water only fenchlorazole was found. The constant neutral-loss scan mode was used to identify carbofuran as TP of FTC. The added value of the proposed procedure is the increased selectivity at the cost of sensitivity. Best results are, therefore, obtained for samples which contain large amounts of matrix constituents.