To further confirm the identity of NISTmAb RM 8671, data from its tryptic digest were submitted for peptide identification. Calculation of the sequence coverage for each tryptic digest produced the same results as those described previously for PS 8670 and lot 14HB-D-001 . For all materials analyzed, sequence coverage of 96.89% was achieved for the heavy chain and 100% for the light chain. This included full coverage of the complementarity-determining regions (CDRs). All post translational modifications identified for the three RM 8671 lots were consistent with those previously reported for PS 8670 . The mass spectrometry results indicated nearly complete pyroglutamination of the N-terminus, moderate levels of the loss of C-terminal lysine, and low levels of glycation, oxidation, and deamidation as previously reported . The similarity of the TIC and UV peptide maps of PS 8670 and RM 8671 as well as the matching peptide identifications confirmed the identity of RM 8671 as conforming to PS 8670.