HIGH RESOLUTION TANDEM MASS SPECTROMETRY IN THE MODERN CLINICAL LABORATORY - DEVELOPMENT AND VALIDATION OF A MULTIRESIDUE METHOD FOR THE QUANTIFICATION OF PSYCHOTROPIC DRUGS IN HUMAN PLASMA

Therapeutic drug monitoring (TDM) plays a crucial role in optimizing pharmacological therapies, especially for drugs with narrow therapeutic windows or high inter-individual pharmacokinetic variability. By combining high sensitivity, selectivity, and multi-analyte capabilities, high-resolution mass spectrometry (HRMS) addresses critical challenges in managing TDM in the clinical lab. In this study, a novel multi-residue analytical method was developed and validated for the quantification of 47 psychoactive drugs, belonging to the therapeutic classes of antiepileptics, antipsychotics and antidepressants, in human plasma. The method combines the use of a small sample volume, a simple protein precipitation protocol with liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS) employing an Orbitrap mass analyzer, which ensured accurate mass measurements and enhanced selectivity. The bioanalytical method demonstrated excellent linearity (r² > 0.99) across clinically relevant concentrations (range: 0.30-3720 ng/mL for antidepressants; 0.03-117 ug/mL for antiepileptics; 0.30-1632 ng/mL for antipsicotics), with lower limits of quantification (LLOQ) ranging from 0,41 – 39,89 ng/ml for antidepressants, from 0,95 – 94,94 ng/ml for antipsychotics and 0,01 – 30,50 ug/ml for antiepileptics. Precision (intra-day and inter-day CV ≤ 6%) and accuracy (bias ± 10 %) met international guidelines for bioanalytical method validation. The Orbitrap-based approach enabled confident identification of analytes through exact mass, isotopic pattern, and high resolution fragmentation spectra (MS/MS). This multiresidue strategy offers a unified, robust and efficient solution for routine TDM in the clinical lab, with potential to support personalized therapeutic interventions and improve patient outcomes