A Liquid Chromatography Mass Spectrometry system comprises: a chromatograph; a mass spectrometer configured to ionize separated fractions of a sample received from the chromatograph; and a programmable processor operable to repeatedly execute the steps of: (i) causing the mass spectrometer to perform a data-independent analysis of the precursor ion species using a mass analyzer of the mass spectrometer; (ii) calculating one or more degree-of-matching scores that relate to detection of an internal standard; and (iii) if each of the degree-of-matching scores meets a respective degree-of-matching condition, performing a quantitative tandem mass spectrometric analyses of both the internal standard and the analyte; the programmable processor further operable to calculate a quantity of the analyte in the sample by comparison between intensities of one or more mass spectral signals generated by the quantitative tandem mass spectrometric analyses of the analyte and the internal standard.