HPLC–DAD determination of opioids, cocaine and their metabolites in plasma

High performance liquid chromatography with diode array detection (HPLC–DAD) was used to develop a method for the simultaneous determination of morphine, codeine, 6-acetylmorphine (6AM), cocaine, benzoylecgonine (BEG), cocaethylene, methadone and its metabolite, 2-ethylidene-1,5-dimethyldiphenylpyrrolidine (EDDP), in plasma. Following solid-phase extraction with Bond Elut Certify cartridges, chromatography was performed on an X-Terra® RP8 column (250 mm × 4.6 mm i.d., 5 μm particle size), using acetonitrile–phosphate buffer pH 6.53 as mobile phase and elution in the gradient mode. The detector response was linear at concentrations over the range 0.1–10 μg/mL in plasma, and the correlation coefficients for the eight drugs studied were all higher than 0.99. The average extraction recoveries from plasma ranged from 60% for BEG to 95% for methadone. The precision was acceptable, with coefficients of variation oscillating between 2.55% and 6.45%. The accuracy was found to be within satisfactory limits (±8.1%). Finally, the method was applied to 21 plasma samples from fatal overdoses, obtaining positive results for two or more drugs.