Centrifugal pipette-tip extraction using pyrolyzed cotton fibers combined with mass spectrometry: High-throughput analysis of methadone and its major metabolite in human urine

A microextraction procedure is presented based on centrifugal-pipette tip microsolid phase extraction using pyrolyzed cotton fibers as sorbent to determine methadone and its major metabolite in urine samples by substrate spray mass spectrometry. The variables affecting the extraction and ionization of the analytes were studied, including the amount of sorptive phase (4 mg), sample volume (1 mL), washing volume (0.5 mL), centrifugation speed (4000 rpm), and eluent (acetonitrile/isopropanol, 1/1). The proposed analytical method was validated yielding limits of detection lower than 1.5 µg/L and demonstrating good linearity (R²> 0.988) up to 150 µg/L. Intra- and inter-day precisions, expressed as relative standard deviation (RSD) and calculated at four concentration levels, were better than 22.7%. Intra- and inter-day accuracy, expressed as relative recovery and calculated at four concentration levels, spanned from 69.5 to 125.3%. The centrifugal-pipette tip extraction allows the simultaneous processing of up to 12 samples in 8 min. This rapid extraction, combined with the short analysis time (< 2 min), provides a high-throughput bioanalytical method. Moreover, the novel microextraction device allows for the processing of up to 2 mL of sample, while the new ambient ionization mass spectrometry (AIMS) interface reduces the void volume, thereby speeding up the analysis time.