Added publication Liquid chromatography coupled mass spectrometry (LC-MS) operating in targeted mass spectrometry (MS) including multiple reaction monitoring (MRM) mode is an accurate analytical method. Integrating with nanoelectrospray-tandem MS (NanoES-MS/MS) and immunoprecipitation (IP), it becomes a promising method in detecting pathogen derived antigens which are at extremely low concentrations, such as mycobacterium tuberculosis (Mtb) secreted 10 kDa culture filtrate antigen (CFP-10). We employed an optimum denaturing condition for trypsin digestion and imunoprecipitation of targeted peptides and applied this method in clinical samples.