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Sodium hydroxide digestion of unhomogenlzed kidney and skeletal muscle for 20 min at 70°C was a superior method for extracting gentamicin from tissues, compared with simple homogenlzatlon, trichloroacetic acid precipitation of homogenized tissue, and sodium hydroxide digestion of homogenized tissue. Fluorescence polarization Immunoassay was used to quantltate gentamicin. Sodium hydroxide digestion of unhomogenlzed tissue allowed for the recovery of 90.0 ± 5.9% (Ẋ ± SD) from renal cortex and 79.9 ± 3.5% from skeletal muscle. The limit of sensitivity was 17.4 ng/g kidney tissue, 15.8 ng/g digested muscle, and 39.0 ng/g digested heart. The wlthin-assay coefficient of variation (CV) at 100 ng/g kidney was 9.2%; at 500 ng/g kidney, the CV was 2.5%; and at 2000 ng/g kidney, the CV was 1.5%. The between-assay coefficient of variation was

A gas chromatographic method for determination of 2-hydroxymethyl- 1-methyl-5-nltrolmldazole (DMZOH), the hydroxy metabolite of dimetridazole, in swine muscle has been developed. The method uses cleanup steps similar to those of an earlier polarographic method. The present method Is capable of quantltatlng levels as low as 2 ppb and detecting less than 1 ppb. Recoveries from 30 control tissues spiked at 1,2, or 4 ppb averaged 80.4%. Performance of the method In Incurred tissue was documented and limited data on the depletion of the metabolite In muscle were generated. The muscle of swine given 150 ppm dimetridazole In feed for 14 days contained less than 1 ppb DMZOH at 12 h withdrawal time.

A high pressure liquid chromatographic method that uses the benzoate ester of cholesterol has been developed for the measurement of cholesterol in foods. A 300 × 3.9 mm id μBondapak C18 column and a variable wavelength ultraviolet detector are used with a 100% methanol mobile phase. Amounts as low as 10 ng cholesterol benzoate can be detected. The results from the analyses of a variety of foods are given and compared with results from gas-liquid chromatographic analyses. The comparison of the 2 chromatographic techniques is favorable.

Recent investigations have clearly established the presence of desaminosulfamethazine (I), N4-acetyl-sulfamethazine (II), and N4-D-glucosyl sulfamethazine (III) in the tissues of swine which have been dosed with sulfamethazine (V). N4(l-Deoxy-DglucuronyDsulfamethazine (IV) has frequently been found in the urine and feces of animals. These metabolites have generally not been investigated in current sulfamethazine methods; therefore, it is not clear to what extent they might be measured by these procedures. Metabolites I, II, III, and IV were synthesized and characterized by several chemical and physical measurements. These metabolites and their parent, V, were added to swine tissue and recoveries were measured by a gas-liquid chromatographic (GLC), a colorimetric, and a gas chromatographic/ mass spectrometric method with electron ionization- selected ion monitoring (GC/MS EI-SIM). With modifications of the gas chromatographic parameters, the GLC method can quantitate compounds I, II, and V simultaneously. If a hydrolysis step is added, all 3 methods can quantitate compound II as V and, in addition, the GC/MS EI-SIM and colorimetric methods can quantitate III as V. In none of these methods do metabolites I, II, III, or IV interfere in the determination of V.

A gas-liquid chromatographic (GLC) method, using the butyryl esters of sterols, has been developed for the measurement of cholesterol, stigmasterol, sitosterol, and campesterol in foods. An immobile phase of 1 % SE-30 coated on 100–120 mesh Gas-Chrom Q packed in a 6′ × 4 mm id glass column operated at 255°C was the most satisfactory of 7 column packings evaluated. Extraction with chloroform-methanol gave 98.7 % recovery with a coefficient of variation of 1.8% for cholesterol added to a variety of foods. When cholesteryl palmitate was added to vegetable oil and the butyryl derivative was prepared, followed by GLC analysis, the recovery was 99.3% with a coefficient of variation of 0.9%. Amounts as low as 1 mg/100 g food can be detected with a precision of 2.5%. The results of the analysis of a variety of foods for cholesterol, campesterol, sitosterol, and stigmasterol are given.

Seven methods were used to compare the efficiency of total lipid extraction from 13 samples of eight different food products. The methyl esters of fatty acids and the butyrate esters of sterols were prepared and analyzed by gas liquid chromatography. On the basis of total lipid recovered and amounts of fatty acids and sterols present, a chloroform: methanol procedure was selected as the most effective method.

Nine brands of mayonnaise and five brands of imitation mayonnaise were purchased from supermarkets in the Washington, DC, area. The samples were analyzed for total fat, fatty acids, sterols, and moisture. Little variation in total fat and saturated fatty acid values was observed among the brands of mayonnaise. The polyunsaturated fatty acid content of mayonnaise ranged from 28.0 to 47.9 g/100 g product. The cholesterol levels were divided between two ranges, 50-55 and 75-79 mg/100 g product. In contrast, there was wide variation in the lipid composition of the different brands of imitation mayonnaise. The total fat values for these products varied from 14.3 to 50.4 g/100 g product. The cholesterol content varied between 0 and 72 mg/100 g product; the latter figure equals the cholesterol content of many of the mayonnaise samples.