A method is described for the determination of 251 pesticide and degradation product residues in fruit and vegetable samples. Extraction of the sample with acetonitrile is followed by a saltingout step. Co-extractives are removed by passing a portion of the acetonitrile extract through an octadecyl (C18) solid-phase extraction cleanup cartridge and then, in a second cleanup, through a carbon cartridge coupled to an amino propyl cartridge. Determination is by gas chromatography with mass-selective detection in the selected-ion monitoring mode, and by liquid chromatography with post-column reaction and fluorescence detection for N-methyl carbamates. The method has been used for analysis of various fruits and vegetables, such as apple, banana, cabbage, carrot, cucumber, lettuce, orange, pear, pepper, and pineapple. Limits of detection range between 0.02 and 1.0 mg/kg for most compounds. Over 80% of the compounds have a limit of detection of ≤0.04 mg/kg.

A method for melengestrol acetate (MGA) was developed to accurately determine 0.08-220 ppm MGA in animal feeds. MGA is extracted from an aqueous slurry of feed sample with hexane and partitioned from hexane into aqueous methanol and then into dichloromethane. After evaporation of the dichloromethane, the dried extract is transferred with chloroform into a volumetric flask. An aliquot is pipetted into a mixed column of silica gel and acid aluminum oxide, and the MGA is eluted with hexane-acetone. The residue is dissolved in methanol, and the MGA is quantitated by reversed-phase liquid chromatography (LC). The method was validated by using commercial feeds and laboratory-fortified feeds. The method was also applied successfully to corn silages supplemented with MGA. Recoveries [and associated coefficients of variation (CVs)] for feeds fortified in the laboratory with MGA 100 at 0.2,0.8, and 5 ppm were 96.9 (6.28), 102 (3.59), and 109% (2.06%), respectively. CVs for a variety of commercial feeds varied from 0.88 to 3.84%. An inter laboratory study was also conducted to compare the LC method to the AOAC gas chromatographic method.