Figure 1: Chromatogram of a typical injection of digested DNA for global methylation using LC-MS/MS. Selected reaction monitoring chromatograms obtained from the LC-MS/MS analysis of human genomic DNA showing deoxycytidine (retention time 1.85 min) and 5-methyl-2’-deoxycytidine (retention time 3.14 min) and their corresponding internal standard peaks. A second peak is observed with identical precursor-product transition as 15N 5-methyl-2’-deoxycytidine which is likely to be uridine (245.1 → 129.1 RT 4.02 min). However this does not interfere with quantitation of 5-methyl-2’-deoxycytidine due to the different retention time. The mass to charge transitions for each analyte are shown alongside the collision energy (in brackets). Abbreviations: RT: Retention Time.