Influence of organic matter and surfactants on solid-phase extraction of diquat, paraquat and difenzoquat from waters

Analysis of diquat, paraquat and difenzoquat in water is performed using solid-phase extraction (SPE) on silica cartridges followed by high-performance liquid chromatographic (HPLC) analysis with a normal-phase column. UV detection with variable wavelength was used to determine each compound at its maximum of absorption providing an excellent sensitivity. Recoveries of these herbicides extracted from 1l of drinking water spiked at levels between 0.1 and 25 mu g/l were higher than 85%. The limits of detection were under 0.1 mu g/l. The effect that the presence of organic matter and surfactants in natural waters has on the extraction procedure was studied. Both, surfactants and organic matter (as humic material), show a negative effect on the recoveries of the herbicides and so their content in natural waters must be controlled.