Determination of pesticides by solid phase extraction followed by gas chromatography with nitrogen–phosphorous detection in natural water and comparison with solvent drop microextraction

The European Union specificies that drinking water can contain pesticide residues at concentrations of up to 0.1 μg/L each and 0.5 μg/L in total, and that 1–3 μg/L of pesticides can be present in surface water, but the general idea is to keep discharges, emissions and losses of priority hazardous substances close to zero for synthetic substances. Therefore, in order to monitor pesticide levels in water, analytical methods with low quantification limits are required. The method proposed here is based on solid phase extraction (SPE) followed by gas chromatography with a nitrogen–phosphorous detector (GC-NPD). During method development, six organophosphate pesticides (azinphos-ethyl, chlorfenvinphos, chlorpyriphos, ethoprophos, fenamiphos and malathion) and two organonitrogen pesticides (alachlor and deltamethrin) were considered as target analytes. Elution conditions that could influence the efficiency of the SPE were studied. The optimized methodology exhibited good linearity, with determination coefficients of better than 0.996. The analytical recovery for the target analytes ranged from 70 to 100%, while the within-day precision was 4.0–11.5 %. The data also showed that the nature of the aqueous matrice (ultrapure, surface or drinking water) had no significant effect on the recovery. The quantification limits for the analytes were found to be 0.01–0.13 μg/L (except for deltamethrin, which was 1.0 μg/L). The present methodology is easy, rapid and gives better sensitivity than solvent drop microextraction for the determination of organonitrogen and organophosphate pesticides in drinking water at levels associated with the legislation.