The linker fragment ion ([ 70 A-K 87 ]+71) 2+ was additionally fragmented more efficiently than ( 1 Z-K 16 )+98) 1+ probably because it is a doubly-charged ions with more availability of mobile protons. Considering the favorable cleavability of the hydrolyzed thiosuccinimide linker, when multiply-charged precursor ions are fragmented the number of protons attached to the resultant P+71 and C+98 linker fragment ions could not be evenly distributed and in consequence their relative fragmentation efficiency could be different.