Dialysate samples were continuously collected with microvial changes every 3 h after portable syringe pump connection on post-operative day 0. At least 24 h after surgery, the microvial was changed pre-temozolomide ingestion and then 1, 2, 3, 4, 6, 8, 10, 12, 14, 16, and 18 h after temozolomide intake on post-operative day 1 and 2. For temozolomide stabilization each microvial was prefilled with 6–12 µl of acetic acid. Microvials containing dialysate samples were stored on dry ice until all microdialysis samples were collected from the patient. Thereafter, the dialysate samples were stored at or below − 70 °C until LC–MS/MS analysis.