Mass Frontier uses search algorithms developed by HighChem and NIST. These algorithms are based on the optimized dot-product function together with an additional term, based on ratios of peak intensities.

The query spectrum can originate from Database Manager, Component Editor, or from Chromatogram Processor by selecting a spectral scan in a chromatogram. In addition, the query spectrum can be pasted from the Clipboard to the search dialog window. In this case the spectrum can be copied to Mass Frontier only.

The Search Spectrum option allows you to choose between Identity or Similarity searches. Identity searching is designed to locate a library spectrum that closely matches an unknown. Similarity searching is done to retrieve spectra library entries of similar compounds when the unknown is either not in the library or its spectrum is distorted so badly that a reliable match is not possible.

After a spectrum search has been carried out the search results (hit list) are stored in the Spreadsheet. The usual result of the spectrum search is a hit list of 100 records. After a search has been completed, a match factor column, with the caption “Match”, will be automatically added to the Spreadsheet. The match factor is a number from 1 to 999 that specifies the measure of similarity between the query spectrum and the library reference spectrum. A Match factor of 999 means a perfect match. To draw your attention to a match greater than 930, a “lightning” icon  is displayed in the Match column in the spreadsheet.

If the Identity search does not provide an acceptable match ( i.e. the unknown has not been positively identified) a Similarity Search may be used. In this case the algorithm does not use the high mass peak index, but employs wider abundance ranges. The hit list resulting from a similarity search can be of value in deducing structure, especially in establishing a structural proposal for an unknown spectrum.

To establish a structural proposal for an unknown, you can switch to the Structures page. From the hit list of similar compounds you may recognize some common structural features, which are displayed in the structures grid. You can copy the structures to Structure Editor and put the pieces of the structural “puzzle” together and so create an initial structure. This structure can be pasted back into a Database Manager window to the record holding the unknown spectrum. After this a comparison of the peaks in the spectrum with generated fragments can provide valuable information about the consistency of the proposed structure and unknown spectrum. If the m/z values of the fragments do not match the spectrum, the structure can be modified and this procedure can be repeated. However, if the structures in the hit list are highly diverse and dissimilar, this approach needs to be combined with other methods.