Stability of benzodiazepines in whole blood samples stored at varying temperatures

Study has been undertaken to determine the stability of four benzodiazepine s: clonazepam, midazolam, flunitrazepam and oxazepam in whole blood samples . Spiked blood was stored at four different temperatures (room temperature, 4 degreesC, -20 degreesC and -80 degreesC) and analysed at selected times during one year. Determination was performed on the first, third and sevent h day during the first week, then once a week for three weeks, once every t wo weeks for four weeks, then once a month for 4 months and finally, once e very 2 months. Extraction was performed using liquid-liquid extraction with 1-chlorobutane, while quantification was carried out using high performanc e liquid chromatography equipped with a photodiode-array ultraviolet detect or. At room temperature, the concentration of all benzodiazepines decreased over one year to 100 and 70% for low and high concentrations, respectively . Al 4 degreesC, the decrease was between 90 and 100% for low concentration s and between 50 and 80% for high concentrations. At -20 degreesC, the meas ured decrease was between 10 and 20% for high and low concentrations, respe ctively. At -80 degreesC, the measured loss was not significant at high con centration except for midazolam. However, at low concentration the determin ed decrease was between 5 and 12%. The data collected suggests that quantit ative results concerning long-term stored samples should be interpreted wit h caution in forensic cases. Further investigations concerning the stabilit y of drugs in whole blood or other biological samples, additional methods o f identification and determination as well as the establishment of optimal storage conditions should be undertaken in forensic cases. (C) 2000 Elsevie r Science B.V. All rights reserved.