The RP-LC-MS Protein Standard is a LC-MS platform standard that is intended to test LC-MS system suitability and intact protein mass measurement. The proteins in MSRT2 are chosen to represent an elution profile for complex proteomic samples. The proteins have been selected based on UV and electrospray response, and are readily observed by both modes of detection. After reconstitution, MSRT2 is an injection-ready standard. MSRT2 can be utilized in studies such as in top-down proteomics.