The accuracy of MS proteoforms identified in both analyses performed with an MS resolving power of 15K and 45K was revealing. Unmodified VP1, VP2, and VP3, were generally more accurately detected using a resolving power of 45K, with all unmodified VPs detected within a mme of ±10 ppm. With a resolving power of 15K accuracy varied depending on column temperature, with unmodified VP identifications having a mme ranging from 1 ppm to > 20 ppm. However, using a resolving power of 15K provided more accurate identification of the A211(Ac)-VP3 variant with separations performed at 25°C and 45°C providing detection within 1 ppm mme. For separation performed at 60°C, the mme was 9 ppm. With a resolving power of 45K, A211(Ac)-VP3 was identified with a mme of 14.7 ppm in separations performed at 25°C, the only column temperature where A211(Ac)-VP3 was identified at this resolution. Accurate identification of oxidized VP proteoforms was more difficult to ascertain. However, an MS resolving power of 45K provided more accurate results. A potential reason for this is that peptide mapping revealed oxidation not only on Met residues, but also on Trp residues. When Met oxidation occurs, the oxidized form is expected to elute after the unmodified form when separation is performed on HILIC . However, as shown in Figure , deconvolution in BPF shows oxidized proteoforms of VP3 (VP3-Ox) eluting over a broad range including before and after unmodified VP3. This suggests that we are seeing oxidation at different sites on VP3 that cannot be differentiated by the HILIC separation and that some of these oxidised sites are potentially at Trp instead of Met residues.