*3.1. Reagents*

Standards of fluoxetine (FLU) and mianserin (MNS) as well as internal standards (IS, nortryptyline and doxepin) were obtained from Sigma-Aldrich (Pozna ´n, Poland), while paroxetine (PAR) and sertraline (SER) were gifts from the National Drug Research Institute, Warsaw, Poland. All the drugs were of high purity grade (>90%). The standard stock solutions of all compounds were prepared in methanol at concentrations of 1 mg/mL and stored at −20 ◦C. Working solutions were prepared ex tempore by dilution of the stock solutions with the culture medium. IS working solution (500 ng/mL) was prepared ex tempore by dilution of the stock solution with acetonitrile. The solvents, namely HPLC gradient grade methanol, MS grade acetonitrile (LiChrosolv) and formic acid 98%, were provided by Merck (Darmstadt, Germany). Ultrapure water was obtained from a Millipore water purification system (Milli-Q water). The pH-dependent octanol-water partition coe fficients (log D) were calculated with logD predictor (https://disco.chemaxon.com/apps).
