Rapid gas chromatographic method for simultaneous determination of cholesterol and alpha-tocopherol in eggs.

A new method was developed for simultaneous determination of cholesterol and alpha-tocopherol in eggs. It involves rapid and simple sample preparation accomplished in one tube and chromatographic separation that does not require derivatization of analytes. Total analysis time per sample is 40 min. Labor, cost, and use of hazardous chemicals are minimized. To ensure selectivity, accuracy, and precision, critical analytical parameters were investigated. Overall recoveries were 98.8 and 99.2% for cholesterol and alpha-tocopherol, respectively. Linearity was acceptable for both analytes (r = 0.9964 for cholesterol and 0.9996 for alpha-tocopherol) in the fortification range examined. Precision data based on within-day and between-days variation gave overall relative standard deviations of 2.0% for cholesterol and 7.0% for alpha-tocopherol. The method was applied successfully for quantitation of cholesterol and alpha-tocopherol in eggs.

Rapid determination of cholesterol in milk and milk products by direct saponification and capillary gas chromatography.

A simple method is described for the determination of cholesterol in milk and milk products. Samples (0.2 g) are saponified in capped tubes with 0.5 M methanolic KOH solution by heating for 15 min at 80 degrees C. Water is added to the mixtures, and the unsaponifiable fractions are extracted with hexane to be further analyzed by capillary gas chromatography. Because of the rapid sample preparation and gas chromatographic procedures, a single sample can be analyzed in 30 min. Overall recovery was 98.6%, and the linearity was excellent for the fortification range examined. Precision data that were based on the variation within and between days suggested an overall relative standard deviation value of 1.4%. The method has been successfully applied to quantitate cholesterol in a variety of milk products.

Albendazole-related drug residues in milk and their fate during cheesemaking, ripening, and storage.

The level and nature of the albendazole residues in milk of treated cows were determined as a function of the time of milking (12-h intervals), and the fate of those residues during cheesemaking, ripening, and storage was examined when the obtained milk was used for making Teleme cheese. Ion-pair liquid chromatographic analysis with fluorescence detection showed that the albendazole sulfoxide metabolite reached its maximum (523 +/- 199 micrograms/kg) at the 1st milking and declined below the detection limit by the 4th milking. The sulfone metabolite attained its highest level (812 +/- 99 micrograms/kg) more slowly (at the 2nd milking) and declined below detection limit by the 13th milking. The 2-aminosulfone metabolite, which was present in the milk obtained at the 1st milking, reached its maximum (128 +/- 36 micrograms/kg) at the 3rd milking, and slowly declined to a level below detection limit by the 15th milking. Whey and cheese analysis revealed that about 70% of each major metabolite initially present in milk could be distributed in the whey. The remaining 30% occurred in the cheese at residue levels higher than those initially present in the milk of the 1st or 2nd milking (688 versus 445 or 450 versus 230 micrograms/kg for albendazole sulfoxide; 890 versus 608 or 1502 versus 783 micrograms/kg for albendazole sulfone; 19 versus 15 or 161 versus 105 micrograms/kg for albendazole 2-aminosulfone). Ripening and storage of the cheeses made from milks from the 1st or 2nd milkings results in a decrease of the sulfoxide metabolite (to 225 or 206 micrograms/kg), an increase of the sulfone metabolite (to 1,181 or 1,893 micrograms/kg), and no effect on the 2-aminosulfone metabolite.

Determination of the marker residue of albendazole in cheese by ion-pair liquid chromatography and fluorescence detection.

A liquid chromatographic method is described that allows quantitative determination of the marker residue of albendazole in cheese. Samples were extracted with acetonitrile, and the extracts were defatted with hexane, evaporated to dryness, reconstituted in ethyl acetate, and purified by partitioning with phosphate buffer. Separation of the sulfoxide, sulfone, and 2-aminosulfone metabolites that constitute the marker residue of albendazole was carried out isocratically with a mobile phase containing both positively and negatively charged pairing ions; detection was performed fluorometrically, with excitation and emission wavelengths of 290 and 320 nm, respectively. Overall recoveries ranged from 73.7 to 84.9%. Precision data based on variation within and between days suggested overall values for relative standard deviation of 3.0 to 3.9%. The sensitivity of the method permitted low limits of detection, particularly for the sulfone and 2-aminosulfone metabolites.

Trace analysis of albendazole and its sulphoxide and sulphone metabolites in milk by liquid chromatography.

Analytical methodology for determination of albendazole and its sulphoxide and sulphone metabolites in milk at levels down to 2-5 ng/ml has been developed. Extraction was carried out with ethyl acetate under alkaline conditions, and extracts were analyzed on a silica-based C18 column in the presence of positively-charged pairing ions. Accuracy data showed overall recoveries ranged from 78.4% to 100%, whereas precision data, based on within and between-day variation, suggested overall precision values better than 4.9%. The method was successfully applied to determine residues in milk of a dairy cow orally given albendazole.

Rapid quantitative screening assay of trace benzimidazole residues in milk by liquid chromatography.

A simple, rapid, and sensitive liquid chromatographic (LC) assay for quantitative screening of albendazole 2-aminosulfone, albendazole sulfoxide, oxibendazole, oxfendazole, albendazole sulfone, p-hydroxyfenbendazole, albendazole, mebendazole, fenbendazole sulfone, and fenbendazole residues in milk was developed. Samples are made basic (pH 10) and extracted with ethyl acetate. Extracts are partitioned with water, evaporated to dryness, reconstituted with mobile phase, and analyzed isocratically by ion-pair reversed-phase LC at 292 nm. Overall recoveries ranged from 79 to 100%. Linearity was excellent in the fortification range examined (5.3-200 ng/mL). Precision data, based on within- and between-days variations, suggested an overall relative standard deviation of 2.0 to 5.8%. The method was successfully used to quantitate albendazole and fenbendazole and metabolites in milk from 2 drug-treated dairy cows.

Rapid ion-pair liquid chromatographic method for the determination of fenbendazole in cows' milk.

A simple and rapid methodology for the analysis of fenbendazole residues in cows' milk, at levels down to 3 ng ml-1, has been developed. Samples are extracted with acetonitrile and centrifuged. The supernatant is de-fatted with isooctane, and mixed with dichloromethane. The separated aqueous layer is discarded, while the bottom organic layer is washed with a phosphate buffer (pH 10) and evaporated to dryness. The residue is dissolved in the mobile phase and analysed by ion-pair reversed-phase liquid chromatography, using octanesulfonate as the ion-pair reagent. Over-all recovery was found to be 99.0%, linearity was excellent and precision data based on within- and between-day variation suggested an over-all variation of 2.0%.