Isolation, identification and determination of cyclophosphamide and two of its metabolites in urine of a multiple sclerosis patient by high pressure liquid chromatography and field desorption mass spectrometry

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Abstract
The off‐line combination of high pressure liquid chromatography and field desorption mass spectrometry has been used for the simultaneous isolation, identification and determination of cyclophosphamide and two of its metabolites, 4‐ketocyclophosphamide and carboxyphosphamide in urine from a patient suffering from multiple sclerosis. Cyclophosphamide and its metabolites were separated using reverse phase liquid chromatography. Field desorption mass spectrometry was employed for identification and quantification. The technique applied needs no derivatization for analysis. The limits of detection by field desorption mass spectrometry for 1, 2 and 3 are a factor of about 4 × 103−105 lower than those of a common variable ultraviolet detector. Quantitative determination was carried out using the method of stable isotope dilution with deuterated analogues of 1, 2 and 3. In a pilot study, the ratio of 1:2:3 was determined to 1:0.02:0.6. One ml of urine is sufficient for simultaneous analysis of the three compounds. The typical analysis time, including separation by liquid chromatography and field desorption measurement, is about 30 minutes.

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