Evaluation of intact mass spectrometry for the quantitative analysis of protein therapeutics.

Implementation of modern analytical techniques, such as intact mass spectrometry, may allow for more detailed quality assessments of protein therapeutics. The complexity of the protein therapeutic manufacturing process as well as the sensitivity of these drugs to different storage conditions can lead to the presence of several undesired products, including truncations, degradation products, byproducts, and differentially modified protein variants that are difficult to detect by peptide mapping. Intact mass spectrometry can be used to identify the intact protein composition, inclusive of post-translational modifications (PTMs) but can also generate a chemical fingerprint of the different protein species present in a given sample. In this work, we systematically evaluated the influence of multiple charge states, multiple isotopes per charge state, and operating resolution on the suitability of intact mass spectrometry for quantitative analysis using insulin and somatotropin as model systems. Standard curves could be generated using absolute intensity data or using the relative ratio between the analyte and internal standard. These methods demonstrate the validity of quantitative intact mass spectrometry for the analysis of protein therapeutic drugs, thus providing a foundation for future comparative methods.