FT-ICR MS spectra of a peptide from a digest of BCCL1 cross-linker treated CA. The un-fractionated reaction (top) and eluted fraction (bottom). Accurate mass measurement of the un-oxidized (m/z = 1266.44365, 6+) and completely oxidized (m/z = 1282.43711, 6+) hanging peptides were in an excellent agreement with the calculated monoisotopic masses (m/z = 1266.44640, 6+ and m/z = 1282.43771, 6+, respectively).