MDZ was incubated at 10 µM for 60 and 120 min with primary human hepatocytes in suspension at 0.05% final DMSO and 0.60% final ACN concentration. Control samples were prepared by quenching the metabolism at 0 min and by performing an incubation at 0 µM followed by spiking after quenching. The final hepatocyte density was 10 6 cells/ml. Two sample preparation procedures were performed. The first approach involved quenching 40 µl incubation volume with two volumes of DMSO. The second involved quenching the same amount of incubation sample with two volumes of ACN/HCOOH 90:10 [v/v]. In both cases the sample was centrifuged for 10 minutes at 4000 rpm. The supernatant was used for LC-MS and LC-IRIS analysis.