Determination of hydramethylnon residues in grass by liquid chromatography with confirmation by liquid...

An improved method for determination of hydramethylnon residues in pasture grass is described. The method uses (1) the hydrochloride salt of hydramethylnon to improve its water solubility and (2) an acid-methanol precipitation to remove chlorophylls while leaving the analyte in solution. The liquid chromatographic method has a validated sensitivity of 0.05 ppm with controls showing < 0.004 ppm. The overall average recovery 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 requiring mass spectrometric confirmation are directly amenable to liquid chromatography/mass spectrometry without additional sample preparation.