Patent ID: 9558922
Date: 2017-01-31
CPC Classifications: G01N,H01J

Claim:
1. A method for determining the concentration ratio of a target peptide in a sample to a reference peptide present in a known amount in a known amount of the sample, the target peptide and reference peptide each having a known elemental composition, and the reference peptide being chemically identical with the target peptide, but having a different isotopic composition, the method comprising: (a) extracting the target peptide and the reference peptide from the sample; (b) acquiring mass spectra of the extracted target and reference peptides in a mass spectrometer, the mass spectra having ion peak distributions specific to the target and reference peptides, respectively; (c) fitting a first family of superimposed bell-shaped curves to the ion peak distribution of the target peptide and a second family of superimposed bell-shaped curves to the ion peak distribution of the reference peptide by varying parameters of the families to find fitted parameter values that minimize differences between the families and the respective ion peak distributions, wherein, in each family, each bell-shaped curve has a predetermined relative height and the curves have fixed distances from each other, the relative curve heights and inter curve distances in the families for the target peptide and the reference peptide being individually determined from one or both of (i) previously measured peak profiles of target and reference peptides and (ii) the elemental composition of the peptides and the respective isotope abundance distributions of elements composing the target and reference peptides, taking into account the purity of the isotopes used for labeling, (d) determining the concentration ratio from the fitted parameter values found in step (c) for each of the first and second families.