Development and validation of a highly sensitive GC/MS method for the determination of buprenorphine and nor-buprenorphine in blood

A sensitive and specific GC/MS method for the determination of buprenorphine (BPN) and its main metabolite nor-buprenorphine (nor-BPN) in blood has been developed, optimized and validated. Sample preparation includes solid-phase extraction of both analytes and their derivatization with acetic anhydride in pyridine. BPN-d4 was used as internal standard for the determination of both analytes. Limits of detection and quantification for BPN and nor-BPN were 0.02 and 0.05 μg/L, respectively. The calibration curves were linear within the dynamic range of each analyte (0.05-30.0 μg/L) with a correlation coefficient higher than 0.996. Absolute recovery ranged from 90.2 to 97.6% for both analytes and their internal standard. Intra- and inter-day accuracy was found to be between -5.40 to 1.73% and -2.45 to 2.80%, respectively, while intra- and inter-day precision were less than 5.8 and 4.7%, for both analytes. The method was applied to real blood samples obtained from patients that follow BPN maintenance program. The developed method can be used in routine every day analysis by clinical and forensic laboratories, for pharmacokinetic studies, for therapeutic drug level monitoring in order to adjust BPN dosage of BPN maintained patients or for the investigation of forensic cases.