Quantification of N, N’ N’’-triethylenethiophosphoramide, N, N’ N’’-triethylenephosphoramide, cyclophosphamide, and 4-hydroxy-cyclophosphamide in microvolume human plasma to support neonatal and pediatric drug studies

•Two LC-MS/MS assays were developed based on the same analytical platform.•A Poroshell PFP column was used enabling a high flow rate and shorter run time (4.5 minutes).•Stabilizing reaction of 4OHCP with semicarbazide is instant even at 4 °C.•The micro-elution solid-phase extraction plate is adopted for small volume samples.•The assays were used for pediatric studies with only 10 µL plasma samples.