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Seven laboratories collaboratively studied a method for the assay of melengestrol acetate at the 0, 10, and 20 ppb levels in bovine fat, liver, muscle, and kidney. The study included fortification of tissue by each laboratory and analysis of fat samples taken from treated heifers which had endogenous levels of 0, 10, and 20 ppb melengestrol acetate. The multistep cleanup procedure used included extraction, solvent partition, column chromatography, and electron capture gas-liquid chromatographic determination. Results of the study for muscle, liver, kidney, and fat showed that the method gave satisfactory recoveries and accuracy. In fat, the most critical tissue, recovery was >93%. A statistical comparison of the results reported for fat tissue from treated heifers demonstrated that 5 of the 7 laboratories obtained similar results. The results produced by the method can be expected to be repeatable within and among laboratories. On the basis of the collaborative results the method has been adopted as official first action.

A high pressure liquid chromatographic (HPLC) method has been developed for determination of sulfamethazine residues in pork liver, kidney, muscle, and fat. The sample was extracted with acetone- chloroform, concentrated in the presence of dilute HC1, and partitioned between dilute HC1 and hexane. The acid solution was washed with methylene chloride and then buffered with trisodium citrate and sodium hydroxide to pH 5.8-5.9. Sulfamethazine was extracted from the aqueous mixture with methylene chloride, concentrated, dissolved in buffer, and eluted from XAD-2 resin with methanol. Sulfamethazine was reliably quantitated at 0.1 ppm by HPLC on a Zorbax ODS column with detection at 254 nm with no interference from tissues or reagents. The average recovery from the edible tissues, i.e., liver, muscle, kidney, and fat, fortified at 0.1-0.4 ppm was 85.6 ± 3.7%.