Single-calibrant quantification of drugs in plasma and whole blood by liquid chromatography-chemiluminescence nitrogen detection

Poor availability of drug reference standards may severely complicate clinical and forensic toxicology investigations. To overcome this problem, a new approach is introduced for drug analysis without primary reference standards. Liquid chromatography-chemiluminescence nitrogen detection (LC-CLND) was employed as the analytical technique, based on the detector's equimolar response to nitrogen and using caffeine as single secondary standard. Liquid-liquid extraction recoveries for 33 basic lipophilic drugs were first established by LC-CLND in blood specimens spiked with the respective reference substances. The mean recovery by butyl chloride-isopropyl alcohol extraction for plasma and whole blood was 90 +/- 18 and 84 +/- 20%, respectively. The validity of the generic extraction recovery-corrected single-calibrant LC-CLND was then verified with proficiency test samples, including 20 different analyses. The mean accuracy was 24 and 17% for the plasma and the whole blood samples, respectively, and the maximum error was 31% for both specimens. All 20 analyses results by LC-CLND fell within the confidence range of the reference concentrations. LC-CLND proved to be an easy-to-use and robust technique, allowing analysis of 1000 injections of biological extracts without a need for major maintenance operations. (C) 2007 Elsevier B.V. All rights reserved.