DETERMINATION OF HYDRAMETHYLNON RESIDUES IN GRASS BY LIQUID-CHROMATOGRAPHY WITH CONFIRMATION BY LIQUID-CHROMATOGRAPHY MASS-SPECTROMETRY

An improved method for determination of hydramethylnon residues in pas ture grass is described. The method uses (1) the hydrochloride salt of hydramethylnon to improve its water solubility and (2) an acid-methan ol precipitation to remove chlorophylls while leaving the analyte in s olution. The liquid chromatographic method has a validated sensitivity of 0.05 ppm with controls showing <0.004 ppm. The overall average rec overy from 0.05 to 0.50 ppm was 98%, with a standard deviation of 11%. Samples showing a positive response (0.05 ppm or higher) and requirin g mass spectrometric confirmation are directly amenable to liquid chro matography/mass spectrometry without additional sample preparation.