Compound Name Precursor Ion Product Ion Dwell Frag-mentor Collision Energy Cell Accelerator Voltage Polarity Retention time (min) Adenine 136.1 92 50 380 10 5 Positive 2.9 Adenine-15N1 137.1 92 50 380 10 5 Positive 2.9 Adenine-15N1 137.1 93 50 380 10 5 Positive 2.9 Adenine-15N2 138.1 93 50 380 10 5 Positive 2.9 Adenine-15N2 138.1 94 50 380 10 5 Positive 2.9 Cytosine 112.1 69 50 380 5 5 Positive 1.6 Cytosine 112.1 69 50 380 5 5 Positive 1.6 Cytosine-15N1 113.1 69 50 380 5 5 Positive 1.6 Cytosine-15N1 113.1 70 50 380 5 5 Positive 1.6 Cytosine-15N2 114.1 70 50 380 5 5 Positive 1.6 Cytosine-15N2 114.1 71 50 380 5 5 Positive 1.6 Guanine 152 135 50 380 10 5 Positive 3.3 Guanine-15N1 153 135 50 380 10 5 Positive 3.3 Guanine-15N1 153 136 50 380 10 5 Positive 3.3 Guanine-15N2 154 136 50 380 10 5 Positive 3.3 Guanine-15N2 154 137 50 380 10 5 Positive 3.3 Guanine-15N3 155 137 50 380 10 5 Positive 3.3 Guanine-15N3 155 137 50 380 10 5 Positive 3.3 Thymine 127.1 110 50 380 14 5 Positive 4.2 Thymine-15N1 128.1 110 50 380 14 5 Positive 4.2 Thymine-15N1 128.1 111 50 380 14 5 Positive 4.2 Uracil 113 70 50 380 13 5 Positive 2.3 Uracil-15N1 114.1 70 50 380 13 5 Positive 2.3 Uracil-15N1 114.1 71 50 380 13 2 Positive 2.3 Adenosine 268.1 136.1 50 380 13 2 Positive 2.4 Adenosine-15N1 269.1 137.1 50 380 13 2 Positive 2.4 Adenosine-15N2 270.1 138.1 50 380 13 2 Positive 2.4 Guanosine 284.1 152 50 380 9 2 Positive 3.3 Guanosine-15N1 285.1 153 50 380 9 2 Positive 3.3 Guanosine-15N2 286.1 154 50 380 9 2 Positive 3.3 Guanosine-15N3 287.1 155 50 380 9 2 Positive 3.3 Cytidine 244 112 50 380 2 5 Positive 1.6 Cytidine-15N1 245 113 50 380 2 5 Positive 1.6 Cytidine-15N2 246 114 50 380 2 5 Positive 1.6 Thymidine 243 127 50 380 2 5 Positive 4.2 Thymidine-15N1 244 128 50 380 2 5 Positive 4.2 Thymidine-15N2 245 129 50 380 2 5 Positive 4.2 Uridine 245 113 50 380 2 5 Positive 2.3 Uridine-15N1 246 114 50 380 2 5 Positive 2.3

Table 1: Details of the Single Reactions Monitoring (SRM) scanning technique on a triple quadrupole mass spectrometer in electrospray ionization positive ion mode.