Patent ID: 7939331

Claim:
A method for quantifying one or more polypeptides comprising: providing at least one sample having one or more polypeptides of interest to be quantified; selecting at least a first polypeptide of interest from said one or more polypeptides of interest; providing a copy of the first polypeptide of interest, the copy made or replicated using recombinant expression and said copy having at least one isotope having a mass different than that of naturally occurring isotopes of the polypeptide of interest; quantifying the copy polypeptide of interest; introducing a known quantity of the copy polypeptide into the sample; analyzing the sample by mass spectrometry; and comparing obtained mass spectrometry peak pairs resulting from the first polypeptide of interest, or one or more fragments thereof, and the copy polypeptide, or one or more fragments thereof, to determine the quantity of the first polypeptide of interest in said at least one sample; wherein the sample is not subjected to an affinity step prior to the analyzing step.