The size heterogeneity and monomeric purity of NISTmAb RM 8671 were analyzed under non-denaturing conditions by SEC with UV detection according to the qualified protocol . The resultant chromatograms for all three RM 8671 lots were consistent in all salient features to that observed previously with PS 8670. The parameters considered were monomeric purity (main peak relative area), high molecular weight (HMW) relative area (RA), and low molecular weight (LMW) RA. Figure 4 and Table S7 (see ESM) present results for PS 8670 during method qualification  compared to the results during value assignment for RM 8671. The CV for monomeric purity is approximately 0.1% in each of the individual lots as calculated from the results listed in ESM Table S7. Standard deviation calculated for intra-vial replicates compared to inter-vial variation on the raw data for main peak purity was also nearly identical (e.g. intra-vial SD = 0.049 vs. inter-vial SD = 0.049 for lot 14HB-D-001 monomeric purity). Collectively this indicates inter-vial homogeneity with respect to monomeric purity was achieved for each individual lot.Fig. 4Homogeneity of RM 8671 lots by monomeric purity (top panel) and high molecular weight relative area (bottom panel), measured by SEC. Error bars represent ±3uc based on ANOVA analysis for each lot (n = 3 for RM 8671 lots) or from intermediate precision data for PS 8670 Qualification 