LC-atmospheric pressure chemical ionization-MS/ MS analysis of multiple illicit drugs, methadone, and their metabolites in oral fluid following protein precipitation.

A quantitative LC−APCI-MS/MS method for simultaneous determination of multiple illicit drugs, methadone, and their metabolites in oral fluid was developed and validated. Sample pretreatment was limited to acetonitrile protein precipitation. LC separation was performed in 25.5 min, with a total analysis time of 35 min. Identification and quantitation were based on selected reaction monitoring. Calibration by linear regression analysis utilized deuterated internal standards and a weighing factor 1/x. Limits of detection and lower limits of quantitation (LOQ) were established between 0.25 and 5 ng/mL and 0.5−10 ng/mL, respectively. Linearity was obtained with an average correlation coefficient (R2) of >0.99, over a dynamic range from the LOQ up to maximum 500 ng/mL. The method demonstrated good accuracy, intra- and interbatch precision, recovery, and stability for all compounds. No oral fluid matrix effect was observed throughout the chromatographic run. Protein precipitation provided a fast and simple sampl...