Applied Biosystems cleavable ICAT(TM) light 227.126983642578125 227.2599945068359375 330.13616943359375 330.399993896484375 Applied Biosystems cleavable ICAT(TM) light C C 10 H 17 N 3 O 3 C 13 H 22 N 4 O 4 S 1 ICAT-C MOD:00480 PSI-MOD Unimod:105 artifact icatlight modification from Unimod Isotopic label isotope tagged reagent derivatized residue