Multiresidue analysis of polar pesticides in surface and drinking water by on-line enrichment and thermospray LC-MS

In the search for a fast and robust sample handling and preparation step to analyse various pesticides at trace levels in aqueous samples, an on-line trace enrichment has been combined with out thermospray LC-MS method allowing both selective identification and a quantification down to the lower ng/L level. 51 polar pesticides were investigated by applying solid phase extraction to 50-100 ml aqueous samples using small cartridges filled with 40mg adsorbent. Prior to their liquid chromatographic separation, the eniched analytes were eluted from the solid phase with the initial methanol/water gradient composition of the HPLC onto the analytical column switching techniques. A base-deactivated C18 material and the two styrene-divinylbenzene copolymers PLRP-S and PRP-1 were tested for enrichment in combination with a C8-bonded silica analytical column. The method developed was evaluated with respect to recoveries, precision, limits of detection and linearity. Furthermore, it was applied to various environmental samples. Apart from a few compounds of higher polarity, most of the pesticides show recoveries >60% (often >80%) with relative standard deviations between 1-15%. Overall method detection limits are in the range of 1-100 ng/L allowing, with one exception, a ready verificiation of the pesticide limit of 100 ng/L set in the EU drinking water guideline.