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Hybrid Similarity Search (HSS) Algorithm for Chemistry Searching for Fentanyl-related compounds and other drugs.
Free version: https://www.mswil.com/images/NIST/NIST17/GCMS-Hybrid-Search-AnalChem-2017.pdf

This is a news from NIST back in March (https://www.nist.gov/news-events/news/2018/03/free-software-can-help-spot-new-forms-fentanyl-and-other-illegal-drugs ) and found with the NIST RSS channel of the Chemical Substances Miner http://www.minerazzi.com/chemsubstances/spp.php

It is a nice example of Information Retrieval applied to Chemistry. They used a modified cosine similarity function. I see possible applications to topic analysis.

Original Source:
Anal. Chem., 2017, 89 (24), pp 13261–13268 DOI: 10.1021/acs.analchem.7b03320

“A mass spectral library search algorithm that identifies compounds that differ from library compounds by a single “inert” structural component is described. This algorithm, the Hybrid Similarity Search, generates a similarity score based on matching both fragment ions and neutral losses. It employs the parameter DeltaMass, defined as the mass difference between query and library compounds, to shift neutral loss peaks in the library spectrum to match corresponding neutral loss peaks in the query spectrum. When the spectra being compared differ by a single structural feature, these matching neutral loss peaks should contain that structural feature. This method extends the scope of the library to include spectra of “nearest-neighbor” compounds that differ from library compounds by a single chemical moiety. Additionally, determination of the structural origin of the shifted peaks can aid in the determination of the chemical structure and fragmentation mechanism of the query compound. A variety of examples are presented, including the identification of designer drugs and chemical derivatives not present in the library.”