Trace determination of organophosphorus pesticides in drinking water using a solid phase preconcentration method coupled on-line to high performance liquid chromatography analysis

In Mexico, as in other countries, the use of chemical pesticides is widely spread. The organophosphorus pesticides are an important source of environmental pollution, since they are highly toxic compounds for living organisms, and the possibility of being in contact with human food is very high. Thus, sensitive analytical methods that can monitor these compounds in drinking water and in human food are highly needed. Gas chromatography using specific detectors like nitrogen-phosphorous is commonly used. However, this technique is not used for the thermally-labile or polar compounds. In these cases, high performance liquid chromatography (HPLC), backed by fluorescence or electrochemical specific detection, is ideal. But only some organophosphorous pesticides (OPPs) have REDOX or fluorescence properties. In these cases, the less specific spectrophotometric detection is recommended. The HPLC has the great advantage to overpass the less sensitive spectrophotometric detection through sample preconcentration based on the liquid-solid extraction. In this paper, the simultaneous determination of traces of several OPPs, metidathion, parathion, methyl-parathion, malathion, fenthion, fenitrothion, isofenphos, metyl-chlorpyrifos, and chlorpyrifos, that are widely used in the country has been done. Reversed-phase on-line liquid chromatography and spectrophotometric detection was used to develop a simple method for determination of 0.2 ppb concentration of these compounds in different drinking water samples, with relative standard deviations less than 10%, using small sample volumes, and without sample clean-up. The use of a diodes array detector was a big help for selecting the optimum wavelength to get the best detection limit for each one of the pesticides.