DETERMINATION OF QUATERNARY AMINE PESTICIDES BY THERMOSPRAY MASS-SPECTROMETRY

Positive-ion (PI) thermospray mass spectrometry (TSP-MS) with methanol-water (50:50) + 0.05 M ammonium formate as eluent was used for the characterization of the quaternary amine pesticides paraquat, difenzoquat, diquat, mepiquat and chlormequat and gave as base peaks [Cat + H]+., [Cat - CH3 + H]+., [Cat]+., [Cat]+., and [Cat]+., respectively. A postcolumn ion-pair extraction system was developed for the determination of difenzoquat from water samples whereas the other quaternary amine pesticides were not extracted. An aqueous mobile phase with various sulphonate counter ions such as dodecanesulphonic acid, methyl orange, Blue Acid 113, Mordant Red 9 and sodium picrate was tested in combination with an extraction solvent containing cyclohexane-dichloromethane-n-butanol (45:45:10) with UV diode-array spectra and PI TSP-MS detection. Applications are reported for the TSP-MS determination of 500 mug/l of difenzoquat in spiked water samples using the postcolumn extraction system. Diquat and paraquat were determined at levels of 0.10-0.17 mug/g in soil samples from the Ebro delta (Tarragona, Spain) using a reversed-phase eluent containing 0.05 M ammonium formate.