Speeding up the process urine sample pre-treatment: Some perspectives on the use of microwave assisted extraction in the anti-doping field

In this contribution we described a fast and efficient method for the liquid/liquid extraction from human urine of different classes of drugs, included in the list of prohibited substances published every year by the World Anti-doping Agency, using microwave irradiation.Liquid/liquid extraction was conducted in a temperature controlled single beam microwave oven equipped with an extraction unit and closed vessels. The effects of microwave power and time on the liquid/liquid extraction process were investigated utilizing different organic solvents. The optimum power was found to be 600 W (generating a temperature of 70 °C) with an incubation time of 30–60 s for the most thermolable constituents such as triamcinolone, prednisolone, chlorthiazide, chlorthalidone, epi-trembolone and oxandrolone, and 1020 W (generating a temperature of 150 °C) with an incubation time of 30–60 s for the other compounds considered in this study.The effectiveness of this approach was evaluated by GC–MS (anabolic steroids, beta2-agonists and narcotics) and by LC–MS/MS (diuretics, glucocorticoids and beta-blockers) analyzing more than 20 different urine samples spiked with the compounds considered in this study. The results showed that the effect of microwave irradiation on the liquid/liquid extraction process was very remarkable: the total sample preparation time can be shortened by 9 min compared to the traditional method (30–60 s instead of 10 min); furthermore, a significant increase in the recovery was recorded for specific compounds such as terbutaline and several diuretics. In addition to the above the repeatability of the extraction recoveries, the limits of detection and the matrix interferences were comparable with the reference methods, presently accredited under the ISO17025, followed by the World Anti-doping Agency accredited anti-doping laboratory of Rome.