Antibodies are used in a broad range of research and diagnostic applications for the enrichment, detection, and quantitation of proteins and their modifications. Hundreds of thousands of antibodies are commercially available against thousands of proteins and their modifications. Unfortunately, many antibodies are poorly characterized, resulting in wasted time and cost as well as potentially flawed research conclusions. To verify the performance and specificity of Thermo Scientific antibodies, we have created a comprehensive workflow to assess antibody specificity using immunoprecipitation combined with mass spectrometry (IP-MS). In preliminary experiments, we screened more than 500 antibodies to nearly 100 key cancer signaling proteins expressed across 12 cultured tumor cell lines. Approximately 70% of antibodies previously validated for immunocapture could be used to capture and identify the intended target, interacting proteins, and off-targets, and ~40% of antibodies not previously validated for IP were positive by IP-MS. To demonstrate the efficacy of these antibodies, we used a set of these antibodies to simultaneously immunocapture twelve proteins in the Akt/mTOR pathway, and then quantified the proteins and their phosphorylation in four IGF-stimulated cell lines using MS-based targeted quantification. Benchmarking of these multiplexed IP-MS assays showed moderate correlation to quantitation with more traditional Western blotting, ELISA, and Luminex assays.