title: Effects of frozen storage on the recovery of clenbuterol from urine samples for official control.
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.
authors.affiliation: Laboratorio de Salud Pública de Lugo, Consellería de Sanidade e Benestar Social, Xunta de Galicia, Lugo, Spain.
authors.forename: P
authors.initials: P
authors.lastname: González-Gigosos
authors.forename: C
authors.initials: C
authors.lastname: Fente-Sampayo
authors.forename: C
authors.initials: C
authors.lastname: Franco-Abuín
authors.forename: A
authors.initials: A
authors.lastname: Cepeda-Sáez
authors.forename: B I
authors.initials: BI
authors.lastname: Vázquez-Belda
mesh_terms: D000318:Adrenergic beta-Agonists / Q000652:urine*; D000818:Animals; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D002976:Clenbuterol / Q000652:urine*; D015925:Cryopreservation; D004350:Drug Residues / Q000032:analysis*; D008401:Gas Chromatography-Mass Spectrometry; D013997:Time Factors
chemical_list: D000318:Adrenergic beta-Agonists; D002976:Clenbuterol