Fig. 2. Examination of the CMCT/D₃-CMCT labelling reaction. Extracted-ion chromatogram and fragment ions of (A) CMCT labelled U, (B) D₃-CMCT labelled U, (C) CMCT labelled m⁵U, and (D) D₃-CMCT labelled m⁵U. The mass transitions 496.3 → 252.2 for CMCT labelled U, 499.3 → 255.2 for D₃-CMCT labelled U, 510.3 → 252.2 for CMCT labelled m⁵U, and 513.3 → 255.2 for D₃-CMCT labelled m⁵U were used for the detection in MRM detection mode.