Simultaneous analysis of five antidepressant drugs using direct injection of biofluids in a capillary restricted-access media-liquid chromatography–tandem mass spectrometry system

Direct analysis, with minimal sample pretreatment, of antidepressant drugs, fluoxetine, imipramine, desipramine, amitriptyline, and nortriptyline in biofluids was developed with a total run time of 8 min. The setup consists of two HPLC pumps, injection valve, capillary RAM-ADS-C18 pre-column and a capillary analytical C18 column connected by means of a six-port valve in backflush mode. Detection was performed with ESI-MS/MS and only 1 μm of sample was injected. Validation was adequately carried out using FLU-d5 as internal standard. Calibration curves were constructed under a linear range of 1–250 ng mL−1 in plasma, being the limit of quantification (LOQ), determined as 1 ng mL−1, for all the analytes. With the described approach it was possible to reach a quantified mass sensitivity of 0.3 pg for each analyte (equivalent to 1.1–1.3 fmol), translating to a lower sample consumption (in the order of 103 less sample than using conventional methods).