Electrospray ionization mass spectrometry of 5-methyl-2′-deoxycytidine and its determination in urine by liquid chromatography/electrospray ionization tandem mass spectrometry

The behaviour of 5‐methyl‐2′‐deoxycytidine (m5dCyd, claimed to be a potential marker for leukaemia) during the electrospray process was studied. In particular, considerations concerning the effect of solution chemistry (e.g. analyte concentration, pH, etc.) on electrospray ionization mass spectra were drawn. Furthermore, a procedure using liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI‐MS/MS) for the determination of urinary m5dCyd is described. The method is simple, sensitive and highly specific. The pre‐treatment procedure gave an average recovery of 79% (relative standard deviation (RSD) of 3%). Method performance was evaluated on spiked urine samples covering the concentration range from 50 ng/mL to 10 µg/mL, the same as that of an existing inhibition ELISA method. Contrary to findings based on this immunoassay technique, urinary m5dCyd in healthy individuals was not detectable and did not increase in the presence of the malignant disease. Copyright © 1999 John Wiley & Sons, Ltd.