Therapeutic monoclonal antibodies (MAbs) are inherently heterogeneous due to a wide range of both enzymatic and chemical modifications, such as oxidation, deamidation and glycosylation which may occur during expression, purification or storage. For identification and functional evaluation of these modifications, stability studies
are typically performed by employing stress conditions such as exposure to chemical oxidizers, elevated pH and temperature.
To characterize MAbs, a variety of analytical techniques are chosen, such as size exclusion chromatography and ion exchange chromatography. However, due to the large size of the intact MAbs, these methods lack structural resolution. Often, the chromatographic peaks resolved by SEC and IEC methods are collected and further analyzed by peptide mapping to obtain more detailed information. Peptide mapping, in which antibodies are cleaved into small peptides through protease digestion followed by LC–MS/MS analysis, is generally the method of choice for detection and quantitation of site-specific modifications. However sample preparation and lengthy chromatographic separation make peptide mapping impractical for the analysis of large numbers of samples. In contrast to peptide mapping analysis, the middle-down approach offers the advantage of high-throughput and specificity for antibody characterization.