Charge variant analysis (CVA) of monoclonal antibodies (mAbs) using cation exchange chromatography is routinely used as a fingerprint of the distribution of posttranslational modifications present on the molecule. Traditional salt or pH based eluents are not suited for direct coupling to mass spectrometry due to nonvolatility or high ionic strength. This makes further analysis complicated when an alteration in the charge variant profile or the emergence of an additional peak is encountered. Here, the use of pH gradient elution using volatile, low ionic strength buffers is reported with direct coupling to high-resolution Orbitrap mass spectrometry. The development of a universal method based on pH elution was explored using a number of mAb drug products. Optimized methods facilitated the separation and identification of charge variants including individual glycoforms of the mAbs investigated using the same buffer system but with tailored gradient slopes. The developed method represents an exciting advance for the characterization of biopharmaceuticals as intact entities through the combination of native charge variant separations with high-resolution native mass spectrometry.
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