Method optimization for the analysis of amphetamines in urine by solid-phase microextraction

Solid-phase microextraction is under investigation in many laboratories for its usefulness in the analysis of an ever widening variety of compounds. As new classes of compounds are investigated and new challenges arise, the methods are adapted to accommodate them. Polar semivolatiles are increasingly under study as analytical targets, and difficulties with small partition coefficients and long equilibration times have been identified. Amphetamine and methamphetamine were selected as semivolatiles exhibiting these limitations, and methods to optimize their analyses were investigated. Amphetamines are frequently monitored in very complex matrixes. Headspace methods minimize interactions between the sample and the fiber and have proven useful for these analyses. Several areas of experimental design were considered in the process of method optimization. These included matrix modification by heating, stirring, methanol content, addition of salt, and pH buffering. It was found that these amphetamines could be reliably analyzed using modified sample conditions, with excellent sensitivity, limits of detection, and method linearity. Clinical urine samples were successfully analyzed and gave clean chromatograms with no interfering peaks. Finally, the method developed was found to be useful for the analysis of narcotic analgesics. In the future, it is hoped that the method can be used to develop a general screen for a wide range of drugs of abuse.