Of the five metrics summarized in Table , two are new to this version of the ILSA: the average spread and Low Fragmentation Protonated Molecule (LFPM) Isotope Ratio Difference (IRD). For a given spectral comparison, peaks from the library spectra are matched to a corresponding peak in the mixture. The spread between the largest and smallest m/z differences between library peaks and their corresponding peak in the mixture is recorded for each spectral comparison, and the average spread is the arithmetic mean of the spread for all available comparisons. The LFPM-IRD, which we colloquially refer to as the IRD, is the difference between the calculated relative intensity isotope ratio between the reference protonated molecule and its major isotope and relative intensity isotope ratio observed with corresponding peaks in the low fragmentation mixture mass spectrum.