Method and apparatus for mass spectrometric immunoassay analysis of specific biological fluid proteins

A method for quantifying the relative amount of one or more specific protein species present in a specimen, comprising the steps of:

• a. combining said specimen with a known amount of internal reference species (IRS) if the specimen does not already contain one;
• b. capturing and isolating at least one of creatine kinase muscle and creatine kinase brain and said IRS, wherein said capturing and isolating step comprises a substep of combining said IRS containing specimen with an affinity reagent;
• c. quantifying at least one of the creatine kinase muscle and creatine kinase brain in which said quantifying step comprises using only mass spectrometric analysis to resolve distinct signals for at least one of the creatine kinase muscle and creatine kinase brain and said IRS to determine the amount of at least one of the captured creatine kinase muscle and creatine kinase brain relative to the IRS.