Application of solid-phase microextraction to antidoping analysis: Determination of stimulants, narcotics, and other classes of substances excreted free in urine

This paper describes the application of solid-phase microextraction (SPME) with subsequent injection in a gas chromatograph–mass spectrometer (GC–MS) (electron impact, full scan) for the screening analysis of stimulants and narcotics in urine. Several d i fferent kinds of fibers were preliminarily tested and comparatively evaluated considering the influence on the overall analytical performance of the method; other experimental parameters; and, primarily among them, the volume of urine, the pH value, and the time of adsorbtion. The optimal experimental conditions have been recorded using 0.5 mL of urine with the pH value adjusted to 10 with carbonate buffer, and in which is immersed a polydimethylsiloxane/divinylbenzene fiber, with a sampling time of 30 min; the fiber is then directly desorbed in the injection port of the GC–MS equipment. All the analytes show a good linearity (R2 > 0.99 for most substances) and a good reproducibility at the concentration corresponding to the minimum performance requirement limit or at the cut-off value fixed by the World AntiDoping Agency (CV% < 11). The limit of detection of the method is 50 ng/mL for the majority of the substances investigated. Imidazole-based drugs (e.g., naphazoline) and local anesthetics can also be included in this screening method. Whenever necessary, confirmation analyses may also be performed by following the same pre-chromatographic procedure. Integrating the SPME process and the GC–MS analysis with a dedicated autosampler that combines the microextraction and injection capacities maximizes the overall analytical capacity of a single GC–MS system and reduces the human labor necessary for and the environmental impact of screening for stimulants and narcotics excreted free in urine.