By Chris Pook
The 2020 version of the NIST library has now been installed on the Metabolomics virtual machine. The library contains a significant increase in spectra, doubling the size of the MS/MS library and adding another ~40,000 spectra to the electron impact library. You can find more details and example spectra on the NIST website.
One of the newest features in the latest NIST Search program is the Hybrid Similarity Search function, described in this paper. The Hybrid search scores spectral matches based on structural similarities by weighting the scores of spectra from compounds that differ by one specific moiety.
Head-to-tail plot comparing mass spectra of 8-chlorocaffeine (top) with caffeine (black and gray peaks in bottom spectrum). The hybrid spectrum corresponds to the black and red peaks in the bottom spectrum. The mass shift from gray to red peaks is DeltaMass (Δm), the nominal mass difference between 8-chlorocaffeine and caffeine. Select shifts highlighted with arrows. From Moorthy et al, 2017.
This new function offers to improve the annotation of unknown features in mass spectrometry datasets by proposing identities for structurally related compounds. MaSH researchers are currently testing this new capability out to see how it can help us assign identities the many features evident in modern mass spectrometry datasets.