Analyte Molecular ion (m/z) Daughter ions (m/z) ADMA 203 46*, 70, 88, 116, 158 d6 ADMA 210 46*, 77, 71, 88, 165 SDMA 203 70*, 116, 88, 165 d5 SDMA 209 70*, 77, 116, 94, 60, 49, 30 NMMA 189 70*, 57 Arginine 175 70*, 60, 43 13C6 Arginine 181 74*, 61, 44, 74 Citrulline 176 159*,70,113 13C5 Citrulline 181 164*,75,118

Table 1: MS spectral characteristics following collision induced disassociation (CID) of arginine metabolites. Following ESI/MS in positive mode, MS spectrum was obtained for each arginine metabolite. The molecular ion and major daughter ions following CID are represented. *represents the most intense daughter ion that was chosen for MRM transition monitoring for quantification.