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We developed a method based on liquid chromatography coupled with tandem mass spectrometry to quantify individual enantiomers of methadone and its primary metabolite, R/S-2-ethyl-1,5-dimethyl-3,3-diphenylpyrrolinium (EDDP), in postmortem blood and brain tissue. Samples were prepared with a Tecan Evo robotic system. Precipitation was followed by solid-phase extraction, evaporation and reconstitution in the mobile phase. Enantiomers were fully separated with liquid chromatography on a chiral α(1)-acid glycoprotein column. A Quattro micro mass spectrometer was used for detection in the positive ion mode with an electrospray source. The lower limit of quantification in brain tissue was 0.005 mg/kg for methadone and 0.001 mg/kg for EDDP enantiomers; the maximum precision was 17% for both compounds; accuracy ranged from 94 to 101%. In blood, the limit of quantification was 0.001 mg/kg for all compounds, the total relative standard deviation was &lt;15%, and the accuracy varied from 95 to 109%. Brain (n = 11) and blood (n = 15) samples were analyzed with intermediate precision that varied from 7.5 to 15% at 0.005 mg/kg and from 6.8 to 11.3% at 0.25 mg/kg for all compounds. Method development focused on producing a clean extract, particularly from brain samples. The method was tested on authentic brain and femoral blood samples.

Chiral Analysis of Methadone and its Main Metabolite, EDDP, in Postmortem Brain and Blood by Automated SPE and Liquid Chromatography-Mass Spectrometry