Comparison of various sample handling and analytical procedures for the monitoring of pesticides and metabolites in ground waters

Various sample handling techniques such as liquid-liquid extraction off-line and on-line, solid-phase extraction followed by either gas chromatography (GC) with electron-capture, flame phorometric or mass spectrometric detection, or liquid chromatography (LC) with diode array detection were applied in the determination of a selected group of insecticides and fungicides in ground water samples at sub-mu g/l levels. An evaluation of the advantages and drawbacks in the application of the proposed methodologies for water monitoring studies is discussed. For the selected group of pesticides studied, off-line C-18 or polymeric cartridges followed by GC-MS using an ion trap analyzer have been revealed as the more powerful technique. But very polar compounds such as methamidophos or acephate have nor been recovered with this procedure. On the contrary, on-line C-18 LC-DAD offered a few drawbacks for the trace determination of a large group of pesticides as a consequence of many important interferences in the chromatographic traces. Other techniques evaluated were LC-MS and GC-MS using a quadrupole analyzer, which offered complementary information and were useful for a limited range of analytes, An interlaboratory study was performed using all the methodologies evaluated in this work and the results obtained showed a good agreement between all the applied techniques. The various methodologies were for a ground water pilot survey study in Almeria (Spain). Endosulfan was the most ubiquitous pesticide detected in this area. (C) 1998 Elsevier Science B.V. All rights reserved.