Fluorometric determination of Ethofenprox in water by using solid-phase extraction

Ethofenprox (pesticide) exhibits a relatively strong fluorescence in the UV region. Its fluorescence properties were investigated in aqueous solution, organic solvents, and micellar media. The fluorescence intensity of Ethofenprox was enhanced by a factor of 1.2 to 2.7 in the presence of surfactants and by 1.4 in pure organic solvents without significant shift of the excitation and emission wavelengths. The conditions for solid-phase extraction of Ethofenprox from water samples were examined. Among the solid-phase extraction cartridges studied, a Sep Pak C8 with weak sorption ability was found to be the most useful due to the extremely high hydrophobicity of Ethofenprox. For the complete elution of Ethofenprox from the sorbent, an addition of 40%v/v methanol to the sample water was necessary and effective to eliminate the fluorescent impurities of the matrix. The calibration graph obtained was linear over the range of 0.03 to 2.4 mg L^-1 in 100 mL sample. The method was successfully applied to the determination of Ethofenprox in tap, well, and river waters with recoveries of 93.2-95.7%.