Brent G. Pautler, Richard Lee & Joe DiMartino
When performing any type of screening assay, one of the most significant analysis challenges lies in the identification of unknown components. While high resolution and high mass accuracy enables greater precision when predicting elemental composition, these estimates lack structural information. When faced with a true unknown, even the fragment ion analysis has limitations and can only highlight particular functional groups at best.
In this work, we present a workflow that utilizes the available analytical information, such as predicted elemental formula, fragment ions and the inclusion/exclusion of known fragments to refine a mass-based local library search (PubChem & ChemSpider). Combining these parameters provides an accumulative filter that reduces search results to a manageable number, or best case scenario, a single structure. The workflow highlighted in this paper uses an unknown pharmaceutical sample as a test case but the software may be applied to samples from any number of sources such as food & beverages, formulated products, metabolomics, and environmental analyses.
Experimental
The pharmaceutical sample was analyzed by HPLC-FTMS (Thermo Fisher Scientific Orbitrap equipped with an electrospray ionization source). The datasets were then loaded into ACD/Spectrus and processed using MS Structure ID. Local versions of the PubChem and ChemSpider databases were used for the mass search. (Note that the ChemSpider library has been curated to include only those chemicals not found within PubChem.) Additional confirmation of the results was then performed.
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