ctrophoresis technique after a liquid-liquid extraction of samples with tert-butylmethylether. A capillary electrophoretic system equipped with a diode-array detector was used for the enantioselective determination of methadone. dextrorphan and -levorphanol were used as internal standards for – and -methadone, respectively. After a liquid-liquid extraction of 1 mL of plasma with tert-butylmethylether, resolution of the enantiomers was performed in an untreated fused-silica capillary of 48.5-cm total length and a standard 50-mm optical path length cell. A constant voltage of 25 kV was applied and the 11423396 cartridge temperature was maintained at 16uC, The diode-array detector was set to monitor the signal at 204 nm. Resolution was performed by using 1 mM heptakis–b-cyclodextrin in 100 mM H3PO4, pH = 2.5 as a running buffer. Calibration curves were prepared for each analytical batch with appropriate volumes of the corresponding racemic mixture working solutions added to test tubes containing 1 mL of drugfree plasma, and were linear over 10000 ng/mL concentration range of the corresponding enantiomers. Control plasma samples containing 150 and 350 ng/mL of methadone enantiomers were prepared in drug-free plasma and were kept frozen at 220uC in 1 mL aliquots until their use. Peak-area ratios between compounds and I.S. were used for calculations. A weighted least-square regression analysis was used. Extraction efficiencies for -methadone and -methadone were calculated by comparing the peak areas of equal purchase BIX-01294 concentrations of drug extracted and non-extracted, being 99.8 and 86.7%, respectively. Four replicate analyses were performed with plasma samples corresponding to the first level of concentrations of the calibration curves, and 3 and 10 standard deviations of the calculated concentrations at this calibration level were used for estimating the limits of detection and quantification, respectively, being LOD 25.9 and 23.2 ng/mL and LOQ 78.5 and 70.2 ng/ mL for and -enantiomer, respectively. Precision was calculated as the relative standard deviation of the quality control samples concentrations and there were 8.9% and 10.2% for – and -methadone, respectively. Accuracy is expressed as the relative error of the calculated concentrations, being 8.2 and 10.9% for and -methadone, 
respectively. Methods Ethics Statement Written informed consent was obtained from each subject after they had received a complete description of the study and been given the chance to discuss any questions or issues. The study was approved by the Ethical and Clinical Research Committee of our institution. Design and Patients The study recruited opioid dependence patients who met criteria for opioid dependence following the Diagnostic and Statistical Manual of Mental Disorders from a MMT program. The main characteristics of the MMT provided included: clinical management with individual counseling to encourage drug abstinence, methadone dosages as required and no restriction on treatment duration. Forced discharge occurred only as a result of patients’ violent behavior or drug trafficking. To be eligible for the study, patients had to be Caucasian, enrolled in MMT for at least four months, and receiving a stable methadone dose for the last two months. Exclusion criteria were as follows: language-related barriers, severe cognitive impairment, and any medical condition that would interfere with research assessments and refusal to take part in the study. Clinical Assessment A close-