Twelve PTM categories were identified (Table ), and their identifications differed significantly (Pearson's Chi-squared test, χ 2 = 196, p-value <2x10 ) depending on the fractionation method. Two-by-two Chi-squared tests were performed to determine which PTMs had significant deviations in their identification rates (observed PTM / the sum of all other PTMs) as described previously. Monomethylation, half cystines, and monohydroxylation were elevated on CZE-MS/MS, while on RPLC-MS/MS, detection of monoacetylated and trimethylation proteoforms was enhanced. PTM observation frequencies at the proteoform spectral match level followed the same trends in observation biases (Table ). Summarized, these observations substantiate the benefit of the combination of CZE and RPLC derived data from increasing the coverage of the proteoform discovery workflow.