Development of Coulometric Mass Spectrometry for Absolute Chemical Quantitation

Abstract

In the past decades, mass spectrometry ( MS )‐based absolute quantitation has become a powerful tool to facilitate advancement in both biomedical and clinical fields. The main advantage of MS‐based quantitation is the accurate and simultaneous quantitation of multiple analytes with high sensitivity. However, a reference material (e.g. authentic target analytes or isotope‐labeled peptide standards) is indispensable for those quantitation methods to build a calibration curve for each analyte, which might not be available or difficult to synthesize especially for some drug molecules with complicated structure or proteins/peptides with post‐translational modification s ( PTM s). To tackle this issue, our group recently developed a standard‐free absolute quantitation approach based on the combination of electrochemistry ( EC ) and MS, involving the coulometric measurement of analyte oxidation/reduction current as well as mass spectrometric measurement of the redox reaction yield. We named the method as coulometric mass spectrometry ( CMS ). Although the combined EC/MS technique is a quickly growing research field in analytical chemistry with numerous distinct applications, the quantitation‐centered application has not been systematically reported. In this review, the principle, apparatus, and various applications of this emerging EC/MS hybrid quantitation method are presented and discussed in detail. An overview of the capabilities of CMS for absolute quantitation across a variety of modalities including small molecule metabolites, peptides, proteins, large molecule biotherapeutics, and PTMs as well as the role of CMS for drug impurity quantitation is provided. Simultaneously, the limitations of the method, which need further optimization and improvement, as well as promising future applications in drug development and proteomics are presented and evaluated.