Method and device for the quantification of target ion species
View Patent ↗Disclosed is a method and device for the mass spectrometric quantification of two or more known target ion species, in which a mass spectrometric signal, composed of signal components of the two or more target ion species, which are not mass resolved in the mass spectrum, is weighted with quantification functions and summed, and a quantification parameter is determined for the two or more target ion species from the weighted sums.
1 . A method for mass spectrometric quantification of two or more known target ion species, each of which has a known mass value which is different for at least two of the species, the target ion species being isobaric fragment ion species produced by fragmentation from precursor ion species labeled with isobaric mass tags, the method comprising the steps:
providing a mass spectrum acquired with a mass spectrometric system from a sample material that produces, in the mass spectrum, a composite signal composed of signal components of the two or more target ion species, which are not mass resolved in the mass spectrum,
providing a plurality of predetermined quantification functions that are linearly independent from one another, wherein a total number of said quantification functions is equal to or greater than a total number of said target ion species,
determining weighted sums by summing the composite signal weighted with the quantification functions,
using the weighted sums as an inhomogeneous part of a system of linear equations, and determining a solution of said system of linear equations in the form of at least one quantification parameter that indicates the relative intensities of the signal components of the two or more target ion species; and
outputting the relative intensities, or ratios of the relative intensities, of each of the measured fragment ion species based on the value of the at least one quantification parameter.
2 . The method according to claim 1 , wherein the quantification functions are (a) polynomials of different order, (b) delta functions or rectangular functions, which are all preferably centered near the respective maximum position of the target ion species, (c) step functions, where each step position is preferably near the respective maximum position of the target ion species, (d) harmonic functions of different periodicity, or (e) functions used for a wavelet transform.
3 . The method according to claim 1 , wherein the signal is composed of the signal components of two target ion species.
4 . The method according to claim 3 , wherein the quantification functions comprise a constant function of value one and a mass axis of the acquired mass spectrum, and the centroid of the signal is calculated from the two weighted sums, where the centroid is used as the input value of a lookup table to determine a ratio of the intensities of the two signal components of the two target ion species.
5 . The method according to claim 3 , wherein the composite signal is weighted with delta functions at each of the known masses of the two target ion species, the weighted sums corresponding to interpolated signal values at the maximum positions of the two target ion species, from whose ratio the ratio of the two signal components of the two target ion species is determined by means of a lookup table.
6 . The method according to claim 1 , wherein the precursor species all have a same species of biomolecule and are each labeled with different isobaric mass tags, each of which has a reporter group and a mass balance group, and where the precursor ion species are isolated from other precursor ion species regarding mass, and optionally isolated regarding mobility in addition, before the fragmentation.
7 . The method according to claim 6 , wherein the isobaric fragment ion species have isobaric reporter groups.
8 . The method according to claim 1 , wherein several mass spectra with the signal are provided, where the weighted sums are calculated separately in each case for individual mass spectra or for partially summed mass spectra before being summed separately according to the predetermined quantification functions to determine quantification parameters therefrom.
9 . The method according to claim 8 , wherein the weighted sums are each calculated separately for each mass spectrum and afterwards summed separately, according to the predetermined quantification functions, to determine the quantification parameters therefrom.
10 . The method according to claim 1 , wherein several mass spectra with the signal are provided, where the weighted sums are calculated separately in each case for individual mass spectra or for partially summed mass spectra, and quantification parameters for the individual mass spectra or partially summed mass spectra are determined therefrom.
11 . The method according to claim 10 , wherein first quantification functions are used for a separate calculation of the weighted sums of a first individual mass spectrum or a first partially summed mass spectrum, and second quantification functions are used for a separate calculation of the weighted sums of a second individual mass spectrum or a second partially summed mass spectrum, where the first and second quantification functions are different.
12 . A device for the quantification of two or more target ion species comprising a data processing unit which is designed and configured to execute a method according to claim 1 .