Simultaneous determination of the herbicides diquat and paraquat in water

A method based on solid-phase extraction (on silica cartridges) and high-performance liquid chromatography (HPLC) followed by diode array UV detection is presented as an analytical tool for screening diquat (DQ) and paraquat (PQ) in drinking waters. The method is useful for quality control laboratories of water companies and beverage industries. Absolute recoveries of DQ and PQ from drinking water (25 mL in all cases), spiked at levels between 0.1, 1.0, and 5.0 microg/L, range from 91% to 103%. Relative standard deviation percentages are between 3% and 11%. Quantitation and detection limits are 70 and 40 ng/L for DQ and 90 and 60 ng/L for PQ, respectively; therefore, these herbicides can be detected and quantitated at levels below the limits established by the European Union.