Carlos Van Peteghem

Determination of Dexamethasone in Urine and Faeces of Treated Cattle with Negative Chemical Ionization - Mass Spectrometry.

For several years, the misuse of dexamethasone and its esters in livestock production has been clearly demonstrated. The first part of the present study deals with the elaboration of a sensitive and specific method for the determination of residues of dexamethasone in excreta at the ppb level. Sample preparation for urine and faeces, including high-performance liquid chromatography (HPLC) fractionation, was carried out. The detection was based on established methodology employing negative chemical ionization-mass spectrometry (NCI-MS) after oxidation of the dexamethasone. In comparison with previous literature, the yield of oxidized dexamethasone was substantially improved and the oxidation procedure was made more simple and robust. In the second part of the study, the relationship between the dose of dexamethasone administered and the levels of the drug in excreta was investigated using this method, as was the ratio between drug levels in urine and faeces. Treatment was carried out for 7 d with an oral dose of 50 mg d-1, the maximum levels found in urine and faeces were 980 and 744 ppb, respectively. While the elimination via faeces responded much slower at the start and the end of treatment, the final part of both excretion profiles were very similar and a level of 1 ppb was reached in both matrices 9 d after the end of treatment. Gas chromatography-mass spectrometry (GC-MS) results obtained for the urine samples were compared with those obtained with direct enzyme immunoassay.

Use of metal chelate affinity chromatography and membrane-based ion-exchange as clean-up procedure for trace residue analysis of tetracyclines in animal tissues and egg

A new and efficient procedure for the clean-up of tetracycline residues in animal tissues and egg prior to reversed-phase high-performance liquid chromatography is described. The principal steps involve homogenization of the tissues in sodium succinate buffer and methanol, followed by centrifugation and clean-up with metal chelate affinity chromatography (MCAC). After further concentration on an Empore extraction membrane with cation-exchange properties, the sample is analysed by HPLC with fluorescence detection. The method was tested on porcine kidney and muscle, bovine liver and whole chickens egg. The recoveries were determined from spiked tissues for oxytetracycline, tetracycline, chlortetracycline and doxycycline and ranged from 40 to 70%, with repeatabilities below 10% R.S.D.. The analytical responses were linear in the range up to at least 1000 ng/g. The detection limits of the method were estimated at 0.42 ng/g of oxytetracycline, 0.49 ng/g of tetracycline, 0.66 ng/g of chlortetracycline and 1.38 ng/g of doxycycline in porcine muscle, using signal-to-noise ratios of 4:1. Similar detection limits were estimated for kidney, liver and egg. The measured limits of quantification were 2 ng/g for oxytetracycline, 3 ng/g for tetracycline, 4 ng/g for chlortetracycline and 5 ng/g for doxycycline in porcine kidney. The advantage of this method over existing methods is its increased limit of detection.

SURVEY OF THE HORMONES USED IN CATTLE FATTENING BASED ON THE ANALYSIS OF BELGIAN INJECTION SITES.

Although the illegal use of orally administered compounds in cattle fattening has gained popularity, injection sites are still frequently found during control experiments on the carcasses in the slaughterhouses. The high concentrations of hormones in injection sites enable screening for the presence of 39 different hormones by a simple extraction followed by a fast and simple high-performance thin-layer chromatography analysis. Analysis of injection-site tissue is particularly successful for determining the hormones that are illegally injected. This data can not be obtained by analysis of other biological matrices like faeces, kidney fat or urine, owing to metabolization and selective excretion and/or deposition of these compounds. Since 1989, over 2000 injection sites have been analysed in our laboratory, which yielded a good survey of the hormones that were illegally injected. Over this period, the natural hormones estradiol and testosterone (mostly present as their esters) have obviously been used extensively. It is clear that since 1990 clostebol acetate has remained the most abused exogenous hormone. Additionally, some distinct trends were noticed, e.g., a tendency towards a highly decreased use of nandrolone, an increased use of progesterone and an increased occurrence of certain androgens like stanozolol and fluoxymesterone.