High-throughput analysis of amphetamines in blood and urine with online solid-phase extraction-liquid chromatography-tandem mass spectrometry

Abstract

An automated online solid-phase extraction-liquid chromatography-tandem mass spectrometry (SPE-LC-MS-MS) method for the analysis of amphetamines in blood and urine was developed and validated. Chromatographic separation was achieved on a Nucleodur® Sphinx RP column with an LC gradient (a mixture of 10 mM ammonium formate buffer and acetonitrile), ensuring the elution of amphetamine, methamphetamine, MDMA, MDA, MDEA, PMA, and ephedrine within 11 min. The method was fully validated, according to international guidelines, using only 100 and 50 μL of blood and urine, respectively. The method showed an excellent intra- and interassay precision (relative standard deviation < 11.2% and bias < 13%) for two external quality control samples (QC) for both matrices and three and two 'in house' QCs for blood and urine, respectively. Responses were linear over the investigated range (r2 > 0.99, 2.5-400 μg/L for blood and 25-1000 μg/L for urine). Limits of quantification were determined to be 2.5 and 25 μg/L for blood and urine, respectively. Limits of detection ranged from 0.05 to 0.5 μg/L for blood and 0.25 to 2.5 μg/L for urine, depending on the compound. Furthermore, the analytes and the processed samples were demonstrated to be stable (in the autosampler for at least 72 h and after three freeze/thaw cycles), and no disturbing matrix effects were observed for all compounds. Moreover, no carryover was observed after the analysis of high concentration samples (15,000 μg/L). The method was subsequently applied to authentic blood and urine samples obtained from forensic cases, which covered a broad range of concentrations. The validation results and actual sample analyses demonstrated that this method is rugged, precise, accurate, and well-suited for routine analysis as more than 72 samples are analyzed non-stop in 24 h with minimum sample handling. The combination of the high-throughput online SPE and the well-known sensitivity and selectivity assured by MS-MS resulted in the elimination of the bottleneck associated with the sample preparation requirements and provided increased sensitivity, accuracy, and precision.