Liquid chromatography combining on-line trace enrichment together with a very selective detection technique is used for the determination of aldicarb, aldicarb sulfoxide, and aldicarb sulfone. Sensitivity is increased by loading a 10 mL volume of ground water on a concentrator column installed in the loop position of a 6-port injection valve. Switching the valves allows the concentrated material to be backflushed onto the analytical column by a methanol-water gradient mobile phase. Separation is followed by post-column hydrolysis to yield methylamine, and formation of a fluorophore with o-phthalaldehyde and 2-mercaptoethanol prior to fluorescence detection. The process requires virtually no sample cleanup and provides good precision on recoveries from different matrixes. Minimum detection limit, defined as 5 times baseline noise, is less than 70 ng/L for the 3 compounds.
