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 ch aracterization of the quaternary amine pesticides paraquat, difenzoqua t, diquat, mepiquat and chlormequat and gave as base peaks [Cat + H]+. , [Cat - CH3 + H]+., [Cat]+., [Cat]+., and [Cat]+., respectively. A po stcolumn ion-pair extraction system was developed for the determinatio n of difenzoquat from water samples whereas the other quaternary amine pesticides were not extracted. An aqueous mobile phase with various s ulphonate counter ions such as dodecanesulphonic acid, methyl orange, Blue Acid 113, Mordant Red 9 and sodium picrate was tested in combinat ion with an extraction solvent containing cyclohexane-dichloromethane- n-butanol (45:45:10) with UV diode-array spectra and PI TSP-MS detecti on. Applications are reported for the TSP-MS determination of 500 mug/ l of difenzoquat in spiked water samples using the postcolumn extracti on 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 r eversed-phase eluent containing 0.05 M ammonium formate.