Thermonicolet Omnic Software User's Guide 6.1 (PDF) - Charles E ...

Searching a
spectral library
Note
Use Search in the Analyze menu (or the Search button in the Library Setup dialog
box) to identify an unknown material. Search compares the unknown sample
spectrum with each reference spectrum in the libraries selected using Library
Setup and finds the spectra that most closely match the unknown. (See “Setting up
a spectral search or QC comparison” for complete information on selecting
libraries and setting the search parameters.)
If you just want to verify the composition of a sample, you can use QC Compare
in the Analyze menu. See “Performing a QC comparison” for details. ▲
You can include the entire unknown spectrum in the search or just certain spectral
regions. The searched regions are determined by three things:
• Which regions you have specified for the library using the Search Regions tab
in the Library Setup dialog box. See “Specifying the regions for a search or
QC comparison” for details.
• Which region of the unknown spectrum you have displayed or selected in the
spectral window.
• Which regions were not blanked when the library was created. See “Creating
a user library” for more information.
Only those portions of the spectrum which are within the selected region (or
displayed region if no region is selected) and within any of the regions you specified
for the library using the Search Regions tab will be included in the search.
The way the search results are displayed after the search depends on how you set
up the search using the Search Results tab in the Library Setup dialog box. For
example, if you specified that the search expert be used, the list of library matches
does not appear unless you click the View Match List button.
If the list of matches is displayed, it shows for each match the library index
number, a match value between 0 and 100, the compound name and the name of
the library that contains the match. The match value tells you how well the library
spectrum matches the unknown. A match value of 100 indicates a perfect match.
The closer the value is to 100, the better is the match.
You can use the Info button to see information about one or more matches in the
list. When you choose Info, a dialog box shows information about the first
selected match. To see information about the next selected match, choose Next.
To see information about the previous match, choose Previous. When you are
finished viewing the information, choose Close.
If you use the search expert, comments about the search results appear in the
lower portion of the Search window.
If you want to change how the search results are displayed, choose Modify
Display. You will be able to specify the number of found library spectra to display
at one time, specify that match values be displayed in the spectra’s panes, or
change the number of compounds shown in the list.
When an exact match is not found, several library spectra may resemble the
unknown spectrum to a similar degree. You can compare the best matches visually
with the unknown spectrum before deciding which is the closest match.
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