Experimental values of molecular masses (MB, MA), IMS drift times (tD) and collisional cross-section (Ω) for dimer and trimer.

Molecular masses (MB, MA), drift times (tD) and collisional cross-section (Ω) values corresponding to dimeric (upper table) and trimeric (lower table) forms detected before (columns 2–5) and after (columns 6–10) reaction with HRP and H2O2. Species are denoted by their charge state z (column 1) assigned by the analysis of the isotopic envelope peak spacing. This allowed a direct calculation of the molecular mass of the species (column 3 and 7) from the average m/z (columns 2 and 6). HRP/H2O2 reaction results in di-Tyr and tri-Tyr covalent cross-link formation with concomitant molecular mass loss of 2 Da per each bond formed. This is illustrated by the observed loss of the mass of the oligomeric form after reaction (column 10). The presented results are mean values from two independent experiments. The maximum difference for m/z (columns 2 and 6) was ±0.025, corresponding to the largest difference of mass values of ±0.175 Da (columns 3 and 7). The largest difference in drift time values was 0.11 for dim8+ signal (dt 6.28) which corresponds to the difference of CCS values of 1.1%. In all other cases the discrepancy between two replicate measurements was lower than 0.9%.