A method for quantitation using data from a mass spectrometer, comprising: acquiring a plurality of full calibration product ion mass spectra for each of a plurality of known quantities of a precursor; determining from the plurality of full calibration product ion mass spectra a plurality of calibration ions that identify the precursor and, determining, for each calibration ion of the plurality of calibration ions, a linear range over which an intensity of each calibration ion of the plurality of calibration ions varies linearly with quantity and a linear function for the linear range; acquiring a plurality of full sample product ion mass spectra for an unknown quantity of the precursor; measuring a sample intensity for each sample product ion of a plurality of sample product ions from the full sample product ion mass spectra; after acquisition of the plurality of the full sample product ion mass spectra for an unknown quantity of the precursor and after measuring a sample intensity for each sample product ion of a plurality of sample product ions from the full sample product ion mass spectra, selecting one or more sample product ions from the plurality of sample product ions that correspond to one or more calibration ions of the plurality of calibration ions such that a sample intensity of each selected sample product ion of the one or more sample product ions is within a linear range of a corresponding calibration ion; and calculating the unknown quantity from one or more sample intensities of the selected one or more sample product ions and one or more linear functions of the one or more calibration ions corresponding to the one or more sample product ions. acquiring a plurality of full calibration product ion mass spectra for each of a plurality of known quantities of a precursor; determining from the plurality of full calibration product ion mass spectra a plurality of calibration ions that identify the precursor and, determining, for each calibration ion of the plurality of calibration ions, a linear range over which an intensity of each calibration ion of the plurality of calibration ions varies linearly with quantity and a linear function for the linear range; acquiring a plurality of full sample product ion mass spectra for an unknown quantity of the precursor; measuring a sample intensity for each sample product ion of a plurality of sample product ions from the full sample product ion mass spectra; after acquisition of the plurality of the full sample product ion mass spectra for an unknown quantity of the precursor and after measuring a sample intensity for each sample product ion of a plurality of sample product ions from the full sample product ion mass spectra, selecting one or more sample product ions from the plurality of sample product ions that correspond to one or more calibration ions of the plurality of calibration ions such that a sample intensity of each selected sample product ion of the one or more sample product ions is within a linear range of a corresponding calibration ion; and calculating the unknown quantity from one or more sample intensities of the selected one or more sample product ions and one or more linear functions of the one or more calibration ions corresponding to the one or more sample product ions.