A sensitive, extractive fluorimetric method for the determination of malath
ion is described. Malathion was hydrolyzed with sodium ethoxide into sodium
dimethyl dithiophosphate (Na-DMDTP), the Na-DMDTP was extracted with Rhoda
mine 6G, a cationic fluorescent dye, as an ion pair into toluene. The fluor
escence of the organic layer was measured at 560 nm after excitation at 536
nm. The method was applied to the determination of malathion residues in w
ater samples up to the ppb level with preconcentration on Amberlite XAD-2.