Abstract: Method for precursor identification from mass spectroscopic data as a function of mass to charge ratio, retention time as well as of ion mobility, using a database of reference precursor data for retrieval of a region of interest for at least three reference peptide precursors in the mass to charge ratio, the retention time as well as in the ion mobility dimension. In a first step for at least three reference precursors, from the database, said data is analysed in the precursor region of interest of mass to charge ratio, retention time as well as ion mobility dimension, and from that analysis empirically an adjusted center in the ion mobility dimension is determined and an ion mobility extraction width window is determined, and in a second step for the identification of further peptide precursors, said extraction width window is used.