Patent ID: 8628977

Claim:
A method for identifying or quantifying a plurality of small molecule analytes, the method comprising: providing a control sample comprising known quantities of a plurality of small molecule analytes, each analyte comprising a different reactive functional group; providing an experimental sample comprising a plurality of said small molecule analytes; dividing the experimental sample into first and second experimental subsamples; adding an amount of the control sample to the first experimental subsample; contacting a first isotopic variant of a labeling reagent with each said analyte in the control sample to yield a plurality of first isotopically labeled analytes, wherein the labeling reagent is covalently linked to the analytes at the different reactive functional groups; contacting a second isotopic variant of the labeling reagent with each said analyte in each of the first and second experimental subsamples to yield first and second experimental subsamples each comprising a plurality of second isotopically labeled analytes, wherein the first and second isotopically labeled analytes are chemically equivalent yet isotopically distinct; adding equal amounts of the control sample to each of the first and second experimental subsamples to yield first and second combined samples; subjecting each of the first and second combined samples to mass spectrometric analysis; and comparing peak intensities generated by the first and second combined samples to identify or quantify the plurality of analytes in the experimental sample.