6x(13)C labeled 4-sulfophenyl isothiocyanate derivatized residue modified L-lysine residue 6x(13)C labeled 4-sulfophenyl isothiocyanate derivatized lysine (12)C 1 (13)C 6 H 5 N 1 O 3 S 2 (12)C 7 (13)C 6 H 17 N 3 O 4 S 2 220.9900054931640625 220.9912109375 349.086181640625 349.089996337890625 4-sulfophenyl isothiocyanate (Heavy C13) K MOD:01335 PSI-MOD SPITC:13C(6) Unimod:464 artifact modification from Unimod Chemical derivative -