Fig. 3.

Sandoz filgrastim drug product (Zarzio®), a biosimilar filgrastim, was subjected to oxidation with (a) 0.1 % and (b) 0.5 % final concentration of H₂O₂, separated on a RP C18 column and electrosprayed into an Exactive mass spectrometer. Peak assignment was performed by detection of diagnostic ions following HCD fragmentation at 35 eV. Peaks labeled in brackets indicate missing fragment ions due to low abundance. The HCD spectra of peaks labeled in red are shown in Fig. 4. The site of Met oxidation can be unambiguously assigned in peaks as low as 0.70 % of total peak area (M138ox + M127ox)