Fig. 7. (a) Site-selective disulfide modification of lysozyme with different functionalities. (b) MALDI-Tof-MS of modified lysozyme with different functionalities: Ly-Ph (calculated: 14 485 [M + H]⁺, found: 14 486 [M + H]⁺), Ly-PEG-Cou (calculated: 14 654 [M + H]⁺, found: 14 653 [M + H]⁺), Ly-PEG-Tz (calculated: 14 694 [M + H]⁺, found: 14 695 [M + H]⁺) (c) MS/MS analysis of the C6 and C127 fragment of Ly-PEG-Tz after trypsin digestion. The expected y and b ions and the zoom-in spectra of the respective fragment ions are given in Section 8.2 in ESI.†.