Dilute and shoot: analysis of drugs of abuse using selected reaction monitoring for quantification and full scan product ion spectra for identification

Abstract

Our objective was to develop a "dilute and shoot" liquid chromatography-tandem mass spectrometry confirmatory procedure that uses full scan product ion spectra to identify drugs that are present above cutoff values as determined by isotope dilution relative to a deuterium-labeled internal standard. Deuterium-labeled internal standards are added to urine which is then diluted prior to analysis. Full scan product ion spectra were obtained in the data-dependent mode using a linear ion trap (ABI 4000 Qtrap). Identification was based on a purity fit of greater than 70. Ninety-seven urine specimens were analyzed by the method described, and results were compared to values obtained from a reference laboratory using selected reaction monitoring (SRM). The ion trap provided about 30-fold increase in signal-to-noise ratio as compared with the same instrument operated in a traditional full scan product ion mode. The assays were linear to at least 10 times the cutoff. Selecting appropriate triggers for obtaining full scan product ion spectra minimized space charging for specimens that contained high concentrations of drugs. There was 100% concordance between the full scan identification and the SRM results for identification of amphetamine, methamphetamine, benzoylecgonine, morphine, codeine, hydrocodone, and hydromorphone. The ability to "dilute and shoot" reduces the turnaround time for results. The data acquired with SRM and full scan product ion spectra provide accurate quantification and a high degree of specificity.