A measured volume of liquid sample, approximately 250 mL, is adjusted to pH 10.5, The sample is extracted using a C8 solid sorbent cartridge or a C-8 disk which has been specially prepared for the reversed-phase, ion-pair mode. The disk or cartridge is eluted with 4.5 mL of an acidic aqueous solvent. After the ionpair reagent is added to the eluate, the final volume is adjusted to 5.0 mL. Liquid chromatographic conditions are described which permit the separation and measurement of diquat and paraquat in the extract by absorbance detection at 308 nm and 257 nm, respectively. A photodiode array detector is utilized to provide simultaneous detection and confirmation of the method analytes.