The NC is a product purified to a lesser degree and contains various impurities next to the non-GalNAcconjugated FLP. Fig. shows the obtained TICs together with 19 EICs of the [M-2H] 2-or [M-2H] 3-ions of different components that could be discerned in the sample. For IP-HILIC-MS, one peak eluted after the NC peak at 14.1 min showing a deconvoluted mass of 5145.62 Da. The difference of 16 Da with the NC (5162.58 Da), suggests the peak at 14.1 min corresponds to a PO impurity. Interestingly, as for the DA-NC, this PO impurity was not separated from the NC peak by IP-RPLC-MS (Fig. ). Most peaks observed had shorter retention times than NC and all revealed masses smaller than the NC, differing 300 Da (i.e. the approximate mass of one nucleotide) or more. These most probably are shortmer impurities, which indeed exhibit shorter retention in both IP-HILIC and IP-RPLC. For IP-HILIC, peaks at 13.0 min and 12.6 min could be assigned tentatively to N-1 (4832.56 Da; loss of dG) and N-2 (4503.53 Da; -loss of 2 dG) impurities, respectively. Tentative assignment of the other observed peaks was not attempted; most likely the underlying species are resulting from two or more failures and/or degradations. Overall, Fig. shows that retention in both IP-HILIC and IP-RPLC increases with ON size, but some specific differences in separation selectivity can be observed. Most essential difference, as indicated above for the DA and PO impurities, is that IP-HILIC is capable of separating impurities that comprise the same number of nucleotides. At the same time, IP-HILIC provides satisfactory separation of the other components, facilitating impurity assignment by MS.