Influence of the storage conditions on the concentration of clenbuterol in cattle urine samples

A study of the stability of clenbuterol in cattle urine samples under different time and temperature storing conditions is reported. At the farm, urine samples were spiked with several amounts of this compound. Then, they were immediately transported to the laboratory and stored at room temperature, between 4 and 8 °C and frozen. Clenbuterol was quantified by using high performance liquid chromatography with diode-array detection (HPLC-PDA) on days 1, 7 and 42 after sample collection. The drug concentration in frozen urine samples was apparently stable during the whole studied period. However, there was a notable decrease in the concentration of this analyte when samples were stored at room temperature and between 4 and 8 °C, specially during the first week. A complementary study showed that the decrease in clenbuterol concentration was particularly significant from 1st to 4th day after sample collection and when urine specimens were kept at room temperature. Based on the results of this study, it was concluded that sample freezing as soon as possible after collection is the most adequate way to guarantee that the reliable concentration of clenbuterol in urine specimens remains unchanging until sample analysis.