Optimized IMAC−IMAC Protocol for Phosphopeptide Recovery from Complex Biological Samples

Immobilized metal ion affinity chromatography (IMAC) is widely used for phosphopeptide enrichment. However, the robustness, efficiency, and specificity of this technique in large-scale phosphoproteomics studies are still disputed. In this study, we first compared three widely used IMAC materials under three different conditions. Fe(III)−nitrilotriacetic acid (NTA) IMAC resin was chosen due to its superior performance in all tests. We further investigated the solution ionization efficiency change of the phosphoryl group and carboxylic group in different acetonitrile−water solutions and observed that the ionization efficiencies of the phosphoryl group and carboxylic group changed differently when the acetonitrile concentration was increased. A magnified difference was achieved in high acetonitrile content solutions. On the basis of this concept, an optimized phosphopeptide enrichment protocol was established using Fe(III)−NTA IMAC resin and it proved to be highly selective in the phosphopeptide enrichment o...