Manual inspection of the spectral comparisons revealed that higher-energy conformers and tautomers occur in about 10-15% of cases. Including these higher-energy geometries by using a tolerance on relative energy (that can be set in the spectral scoring procedure) improved the performance by assigning geometries that were not considered before. However, as a trade-off, for metabolites that match well, the inclusion of more candidates reduces the correct identification rate. An intermediate energy cut-off of about 10 kJ/mol was found to yield optimal results. Isomeric mixtures have not been addressed, but experiments involving LC, IMS or 2-color laser spectroscopy are expected to reduce such cases. The utility of the in silico IR spectral library was demonstrated in the identification of a human plasma metabolite as 3-hydroxyhexanoic acid.