During the past decade, mass spectrometry, notably LC/MS, has become a major approach to identify and quantify proteins in patient samples. It includes analysis before treatments to find the proper biomarkers for cancers diagnostics, and monitoring of the arising of the anti-drug antibodies in human plasma after therapies. Despite the fact that MS has pretty high sensitivity and specificity, research in biotherapeutics requires even more. Immunocapture, and so specific protein enrichment, offer an interesting immunoassay solution. Here, we present simple to use and efficient reagents to improve the immunocapture and thus the output of the MS technology.