|Unique similarity searches allow to approach structures of compounds
having no reference in the libraries. The search of hypothetical structures
(or of a similar structure found on a hitlist if no structure input is
available) gives the most relevant (closest) spectra back from the libraries.
The careful comparison of these reference spectra with the unknown spectrum
serves to verify, falsify or modify the hypothetical structure.
|The MassLib searches are especially designed to be insensible against
minor distortions of the spectra. This allows to search most efficiently
spectra of every vendors spectrometers in the commercial general purpose
libraries. MassLib searches do also handle the nasty problem of many duplicates
and poor quality of library entries. These spectra do not stay in front
but they remain viewable and searchable.
|MassLib allows the easy inspection of duplicates and isomers to a hit
found on search lists.
|MassLib searches may get restricted for identity using a retention
index window, provided the user calibrates his analysis for retention index
using MassLib's retention index tools.
|MassLib searches standard spectra (fragment masses and intensities):
|The SISCOM Search for Identical
and Similar Compounds is not a retrieval search!
It provides various rankings:
Identity (regrouped) recognises binary mixtures (if both components
are in the library) and switches over automatically to similarity if no
identical spectra are found.
Similarity combines visual identity and Characteristic Ion based
Related (used if no very similar references were found) provides
the library spectra matching best with respect to the Characteristic Ions.
|See a search example !
Neutral Loss Masses (mass
differences to M+) are used with ease to verify the molecular ion region.
Here a tool has a comeback every mass spectroscopist used before getting
computerised: indeed, neutral loss masses are useful to sort out interesting
entries in fragment mass search hitlists to find structurally close entries.
Two tool buttons are actually provided: the one with a ‘n’ marked ‘distance’
is used to draw mass differences in between two peaks and the one showing
two interleaved arrows is used to revert the direction of the mass scale
and to align M+ peaks in multiple spectra displays.
|Have a look at the neutral loss display
|MassLib searches neutral losses (mass differences to M+):
|As frequently neutral masses contain complemental information to fragments,
this search is able to provide complemental structure information quite
frequently. Interestingly enough it does sometimes work also if applied
to prominent peaks other than M+. Here now fragment masses serve to recognise
most important hitlist entries (important with respect to structure).
|MassLib searches structures edited using MassLib's structure
|imported as Molfile.
Also structures stored in libraries may get searched.
The vast hitlist contains normally 200 entries and provides the very
best spectra of the libraries for comparison to an unknown spectrum (potentially
not present in the libraries). This is most useful if the structure searched
was the result of the combined structural information gathered using the
spectrum searches (fragments and neutrals) discussed above.
As the structure search also finds spectra of very poor quality (e.g.
just eight basepeaks), more spectra of large libraries become useful: Good
as these are for comparison purposes they do normally not show up
in spectrum searches.
These spectra of good or poor quality allow to learn how differences in
structure influence the spectrum (structurally closely related to the structure
of the unknown!).
These spectra allow to discard or to modify the hypothetical structure
of the unknown.