Validation of an LC–MS–MS method for analysis of 58 drugs of abuse in oral fluid and method comparison with an established LC–HRMS method

Liquid chromatography-mass spectrometry (LC-MS) methods for detection of multiple drugs of abuse (DoA) in oral fluid (OF) samples are being implemented in many clinical routine laboratories. Therefore, there is a need to develop new multianalyte methods with simple sample pretreatment and short analysis times. The purpose of this work was to validate a method detecting 58 DoA to be used with two different OF sampling kits, the saliva collection system (SCS) from Greiner Bio-One and Quantisal from Immunalysis, using the same sample pretreatment and analytical method. A set of 110 samples collected with the SCS kit was further compared to an high-resolution mass spectrometry (LC-HRMS) method in another laboratory. The method was successfully validated, with precision and accuracy of ≤15% and z-scores of <2 for external controls. Using a sensitive LC-MS-MS instrument, the detection limits were <1 µg/l in neat oral fluid. In the comparative study between the LC-MS-MS and LC-HRMS methods using SCS samples, a good agreement was observed. Discrepancies were limited to lower concentration ranges, attributable to differences in cut-off thresholds between the methods. This work contributes to the development of LC-MS multianalyte methods for OF samples, which are suitable for clinical routine laboratories.