has_metric_category single value ID based metric single run based metric ion source metric MS2 metric median MS2 precursor charge in identified spectra MS2 known precursor charges fractions MS:4000176 MS2-PrecZ-more Median MS2 precursor charge in identified spectra. The used type of identification should be noted in the metadata or analysis methods section of the recording file for the respective run. In case of multiple acceptance criteria (FDR) available in proteomics, PSM-level FDR should be used for better comparability. MS2-PrecZ-1 MS MS2-PrecZ-4 MS2-PrecZ-5 MS2-PrecZ-2 MS2-PrecZ-3 Higher charges may indicate inefficient ionization and/or e.g. preference for longer peptides in relation to identifiability.