Combined liquid chromatography-coulometric detection and microextraction by packed sorbent for the plasma analysis of long acting opioids in heroin addicted patients

The sublingual combination of buprenorphine and naloxone (Suboxone®) and Methadone Maintenance Therapy have been found effective in treating heroin addiction. A new analytical method suitable for the simultaneous determination of buprenorphine, norbuprenorphine, methadone and naloxone in human plasma by means of liquid chromatography with coulometric detection has been developed. The chro- matographic separation was achieved with a phosphate buffer–acetonitrile mixture as the mobile phase on a cyano column. The monitoring cell of the coulometric detector was set at an oxidation potential of +0.600 V. A rapid clean-up procedure of the biological samples using a microextraction by packed sorbent technique has been implemented, employing a C8 sorbent inserted into a syringe needle. The extraction yield values were satisfactory for all analytes (>85%). The calibration curves were linear over a range of 0.25–20.0 ng/mL for buprenorphine and norbuprenorphine, 3.0–1000.0 ng/mL for methadone and 0.13–10.0 ng/mL for naloxone. The sensitivity was also high with limits of detection of 0.08 ng/mL for both buprenorphine and norbuprenorphine, 0.9 ng/mL for methadone and 0.04 ng/mL for naloxone. The intraday and interday precision data were always satisfactory. The method was successfully applied to plasma samples obtained from former heroin addicts treated with opioid replacement therapy.