LC-MS-based quantification of intact proteins: perspective for clinical and bioanalytical applications

Bioanalytical LC-MS for protein quantification is traditionally based on enzymatic digestion of the target protein followed by absolute quantification of a specific signature peptide relative to a stable-isotope labeled analog. The enzymatic digestion, nonetheless, limits rapid method development, sample throughput and turnaround time, and, moreover, makes that essential information regarding the biological function of the intact protein is lost. The recent advancements in high-resolution MS instrumentation and improved sample preparation techniques dedicated to protein clean-up raise the question to what extent LC-MS can be applied for quantitative bioanalysis of intact proteins. This review provides an overview of current and potential applications of LC-MS for intact protein quantification as well as the main limitations and challenges for broad application.