Effects of frozen storage on the recovery of clenbuterol from urine samples for official control
The effects of storage under frozen conditions on clenbuterol recovery from spiked calf urine samples were studied. Urine samples contaminated with 10 µg l–1 clenbuterol and frozen at –15°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°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 µg l–1 (17%) clenbuterol on the 180th day in samples stored at –15°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.
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Document Type: Research Article
Affiliations: Laboratorio de Salud Pública de Lugo, Consellería de Sanidade e Benestar Social, Xunta de Galicia, Lugo, Spain
Publication date: November 1, 2002