1. A method for performing a mass analysis of a subset of ions generated from a sample, the subset of ions comprising a restricted range mass-to-charge (m/z) ratios of the generated ions, the method comprising the steps of (i) performing a survey mass analysis using a mass analyzer of a mass spectrometer so as to identify the restricted range of m/z ratios and to measure a flux of ions having m/z ratios within said restricted range and (ii) performing a dependent mass analysis of an optimal quantity of ions having m/z ratios within said restricted range, said optimal quantity of ions collected for a time period determined by the measured ion flux, the method CHARACTERIZED IN THAT: the time period is determined using a corrected ion flux that is calculated from the measured flux of ions, wherein the correction accounts for, during the dependent mass analysis, one or more of: (a) imperfect restriction of collected ions to the range of m/z ratios, (b) the use of different mass analyzers for the survey and dependent mass analyses, and (c) one or more ion pathways that differ from those used during the survey mass analysis; and wherein the correction accounts for ion collection that includes ions within the range of m/z ratios that are undetected by the survey mass analysis, wherein the survey mass analysis is performed by an electrostatic trap mass analyzer.