Application of mobile phase additives to reduce metal-ion mediated adsorption of non-phosphorylated peptides in RPLC/MS-based assays

Metal-ion mediated adsorption in liquid chromatography has been identified as a contributing factor in poor peak shape, tailing, and diminished recovery of compounds prone to cation exchange-like interaction with metal-based activity sites. Peptides that exhibit negative charge-bearing amino acids such as aspartic acid and glutamic acid are particularly sensitive to metal-ion mediated adsorption in RPLC/MS-based separations when using weak acids (e.g. formic acid) as mobile phase additives. Citric acid and medronic acid as metal complexing mobile phase additives were evaluated for their ability to mitigate metal-ion mediated adsorption in RPLC/MS-based peptide mapping assays. In this study, chromatographic performance was stabilized with peak tailing for peptides of interest reduced by as much as 40% in the presence of a chelator at a mobile phase concentration of 1 ppm. Performance gains were observed to be stable over a 67-hour time study with an average USP tailing factor of 1.00, % RSD = 0.64. The stabilizing effect of the chelator improved peptide mapping assay robustness with relative peak areas for target impurities calculated at 2.28% (% R.S.D. = 2.36) and 2.40% (% R.S.D. = 2.37). Collectively this study demonstrates that chelators as mobile phase additives offers a means to improve chromatographic performance for biomolecules sensitive to metal-ion mediated adsorption under formic acid-based RPLC conditions.