Patent ID: 8321153

Claim:
A non-transitory computer readable medium having computer executable code stored thereon which, when executed, causes a computer to perform a method comprising: determining a probabilistic model of an isotopic cluster; finding isotopic clusters from mass spectra; and determining monoisotopic masses of the isotopic clusters, using the probabilistic model, wherein the step of determining the probabilistic model of an isotopic cluster comprises: approximating an intensity (I k ); determining an intensity of a k th peak in the isotopic cluster (I k ), a ratio (I k+1 /I k ) of two peak intensities, and a ratio product ( I k - 1 ⁢ I k + 1 I k 2 ) of two ratios obtained from three peaks, using probabilistic equations; and determining maximum, minimum and average functions (R max (k, M), R min (k, M) and R avg (k, M)) for the k th ratio of a polypeptide having a mass of M, and maximum, minimum and average functions (RP max (k, M), RP min (k, M) and RP avg (k, M)) for the ratio product of the k th ratio of the polypeptide having the mass of M, wherein I k+1 is an intensity of a peak with a mass 1 Da larger than I k , and I k−1 is an intensity of a peak with a mass 1 Da smaller than I k .