IMPROVING THE SOLID-PHASE EXTRACTION OF QUAT PESTICIDES FROM WATER SAMPLES - REMOVAL OF INTERFERENCES

A novel strategy, based on the addition of a cationic surfactant, for preventing the interferences associated with a diminution in the effic acy of solid-phase extraction (SPE) with silica cartridges of diquat, paraquat and difenzoquat in water is developed. Conditions for extract ion are optimised with respect to pH, cationic surfactant and its conc entration. Humic acids, anionic surfactants, inorganic salts and other organic contaminants like pesticides, phenols, polycyclic aromatic hy drocarbons and polychlorinated biphenyls produce the studied interfere nces. The best performance is shown in the improvement of the ''quats' ' recovery from waters with high levels of humic acids and anionic sur factants (recovery is increased from ca. 30% to more than 80%). Unfort unately, the strong interference from inorganic salts remains. The pre sence in the water sample of other organic contaminants only affected the extraction efficiency of difenzoquat at high concentrations (more than 1 mg/l). Analytic utility is illustrated by selective measurement s of the three herbicides, in real water samples. Overall, the results show that in spite of its drawbacks, SPE is a useful technique that a llows the detection and quantification of the ''quats'' at limits belo w 100 ng/l as established by the European Union. (C) 1998 Elsevier Sci ence B.V. All rights reserved.