Determination of plasma concentrations of underivatized cyclophosphamide by capillary gas chromatography.

A sensitive method for the clinical determination of cyclophosphamide in 0.2 ml plasma by capillary gas chromatography with nitrogen-phosphorus detection is described. A detection limit of 50 nl/ml is readily obtainable, which is sufficiently low to measure the cyclophosphamide concentrations occurring in clinical practice. The selection of internal standards and the use of the nitrogen-phosphorus detection system is discussed, as well as eventualities for determination of cyclophosphamide metabolites.