Quaternary amines are challenging to determine due to their strong interaction with cation-exchange columns and chemical similarity. In addition, some quaternary amines are polar pesticides with toxic and environmental concerns. Here we demonstrate direct determinations of four quaternary amine polar pesticides in food products using a high-performance cation-exchange column designed to resolve quaternary amine pesticides and inorganic cations. The polar pesticides are serially detected by suppressed conductivity and Selective Reaction Monitoring (SRM) of the product and reaction product ions. The pesticides were separated using an electrolytically generated methanesulfonic acid gradient from 3 to 25 mM at 0.3 mL/min and 40 °C. After passing through an electrolytic suppressor, which replaces the acid anion with hydroxide to form water, the pesticides were detected by suppressed conductivity and ionized by positive ESI-MS without make-up solvent for detection by MS. <br/><br/>The method was applied to ground, acid-methanol extracted, diluted oat cereal samples following a modified Quechers Polar Pesticide (QePPe) method. Chlormequat was extracted with formic acid whereas paraquat and diquat were extracted with hydrochloric acid. The four quaternary amine polar pesticides exhibited good peak shape with peak asymmetries from 1.0 to 1.1 As(EP) and eluted from the column within 20 min with baseline resolution. The two types of oat cereal samples did not contain paraquat, diquat, mepiquat, or chlormequat. Recoveries of spiked in reagents were ~80%. Sensitivities, as judged by the limits of detection, were single digit µg/L.

Determination of quaternary amine polar pesticides using improved cation-exchange separation technology combined with suppressed conductivity and tandem mass spectrometry detection

ACS Spring 2022

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