ABSTRACT
The effects of storage under frozen conditions on clenbuterol recovery from spiked calf urine samples were studied. Urine samples contaminated with 10 micro g l(-1) clenbuterol and frozen at -15 degrees C were analysed every 15 days over 6 months. A single frozen contaminated urine sample was also thawed every 15 days over 3 months for the analysis of 10-ml aliquots, after which the remaining portion was frozen again (-15 degrees C). The presence of clenbuterol was determined by GC-MS. A gradual decline in clenbuterol recovery was observed from the first to the 180th day. It was only possible to recover 1.74 +/- 0.06 micro g l(-1) (17%) clenbuterol on the 180th day in samples stored at -15 degrees C. Likewise, clenbuterol totally disappeared from spiked urine samples that had been successively frozen and thawed over 3 months. The results were confirmed in a study performed on 2704 calf urine samples collected on farms and analysed by HPTLC and GC-MS. Of 73 positive samples, 61 had been frozen for <10 days.
Subject(s)
Adrenergic beta-Agonists/urine , Clenbuterol/urine , Cryopreservation , Drug Residues/analysis , Animals , Cattle , Chromatography, High Pressure Liquid , Gas Chromatography-Mass Spectrometry , Time FactorsABSTRACT
A new method for the determination of clenbuterol by reversed-phase HPLC with UV detection has been developed. Clenbuterol was eluted on a C8 column (250 x 4.6 mm I.D), using an isocratic eluent consisting of an acetonitrile -0.02 M phosphate buffer (25:75, v/v) adjusted to pH 2.8 with phosphoric acid. The method was linear from 2.5 to 50 ng injected. The detection limit was established to be 0.5 ng (signal/background ratio: 3), and the quantification limit was 2.5 ng. With the proposed method, we got a simple and rapid detection of clenbuterol in the retina, part of the animal where the biggest amount of clenbuterol is accumulated and where it remains for the longest time after any treatment.
Subject(s)
Clenbuterol/chemistry , Retina/chemistry , Animals , Aqueous Humor/chemistry , Calibration , Chromatography, High Pressure Liquid , Drug Residues/chemistry , Rats , Spectrophotometry, Ultraviolet , UltracentrifugationABSTRACT
The agar dilution method was used to determine the activities of gentamicin, erythromycin, streptomycin, chloramphenicol, ampicillin, sulfamethazine, cephalothin, penicillin G, and tetracycline against 73 strains belonging to the genus Listeria (L. innocua, L. seeligeri, and L. monocytogenes). All strains were isolated from raw milk, cheese, the dairy processing plant, poultry, and the poultry slaughterhouse. Gentamicin, ampicillin, and erythromycin, of which the MICs for 90% of the strains tested for all three species were < or = 5.96 micrograms/ml, were found to be the most active agents studied. Most of the L. innocua strains isolated from poultry and the poultry slaughterhouse were resistant to tetracycline.
