The example in Figure demonstrates the potential of IRIS-based identification of known unknowns, based on the inherent sensitivity of an IR spectrum to chemical structure. Not only is the correct metabolite ranked best (known unknown identification), but the search also assigns high scores to entries that are structurally similar. This inherent link between structure and spectroscopy provides venues towards the identification of unknown unknowns. Searching the entire IR library with an adduct constraint, but releasing the constraint on chemical formula (i.e., on exact mass), should assign high spectral similarity scores to compounds with high structural similarity to the unknown, even if the elemental composition is not the same.