Quantifying the Unquantifiable with Mass Spectrometry

Mass spectrometry is a commonly employed platform for quantifying analytes. For polymers and complicated mixtures, the lack of standards and the difficulty in representing the large intact molecule make quantitation difficult if not impossible.

In this presentation, the quantitation of previously unquantifiable analytes will be described. These analytes include polysaccharides, large protein mixtures and their posttranslational modifications, and complicated mixtures such as oligosaccharides in human milk.

Polysaccharides are digested by a chemical enzyme and the resulting oligosaccharides are used to quantitate the intact polysaccharide using LC-MS and dynamic MRM methods. Human milk oligosaccharides are quantified using a selected number of standards and interpolating the abundances of those without standards to obtain the absolute abundances of nearly a hundred analytes.

Protein mixtures are quantified using total protein quantification method while further employing these values with selected protein standards to obtain absolute quantitation of hundreds of proteins in bovine milk. Additionally, quantitation of glycan modification on proteins using dynamic MRM monitors the glycosylation of individual sites on proteins in serum.

Presenter:  Carlito Lebrilla, Ph.D. (Professor of Analytical Chemistry, University of California at Davis)

Dr. Carlito B. Lebrilla is a Distinguished Professor at the University of California, Davis in the Department of Chemistry and Biochemistry and Molecular Medicine in the School of Medicine. He received his BS degree from the University of California, Irvine and Ph.D. from the University of California, Berkeley. He was an Alexander von Humboldt Fellow and a NSF-NATO Fellow at the Technical University in Berlin. He returned to the UC Irvine as a President’s Fellow and has been at UC Davis since 1989. He has served as Chair of the Chemistry Department. His research is in Analytical Chemistry, primarily mass spectrometry with applications to clinical glycomics and biofunctional food. He has nearly 400 peer-reviewed publications. He is also Co-Chief editor of Mass Spectrometry Reviews and has been on the editorial board of Molecular and Cellular Proteomics, Mass Spectrometry Reviews, Journal of American Society for Mass Spectrometry, European Mass Spectrometry, and International Journal of Mass Spectrometry.