Preparation of reference materials for anti-doping control: study of the lyophilisation conditions.

Abstract

Urine reference materials used in interlaboratory comparison must be homogeneous and stable over time. The lyophilisation process is one of the methods applied when preparing urine reference materials for ensuring stability during distribution, transport and storage. Urine samples of 11- nor- Δ9- tetrahydrocannabinol- 9- carboxylic acid (THC-COOH), Benzoylecgonine (BE), Ethyl glucuronide/Ethyl sulphate (EtG/EtS) and ethanol (EtOH) were prepared from blank urine previously filtered. Samples were fortified with the adequate standard solutions and they were divided in aliquots. Aliquots stored at 4 ºC and lyophilized aliquots were used to evaluate the homogeneity of the samples. Others were frozen at -20 ºC and they were used as reference aliquots. In the first analysis, all prepared samples, except EtOH sample, were considered homogeneous. Concentration differences of THC-COOH and BE between lyophilized aliquots and reference aliquots were minimum (lower than 5 %). However, differences higher than 8 % were observed for EtG/EtS. If these differences were maintained constant in subsequence quantifications, they could be attributed to the evaporation of the analytes during the lyophilisation process. Results obtained for EtOH sample show a completely loss of the analyte due to its high volatility.