12
Spectrum identification
ZaIR 3.5
allows for identifying compounds by their IR spectra, name or other data by
searching the spectrum libraries (libraries are not part of the system and are supplied
separately). Click on the
Spectrum Search
button or press
F5
to start searching an open
spectrum. In case of multiple open spectra, the first one is used. The search time depends on
the number of search libraries and computer capacity and does not usually exceed two
seconds. The button remains clicked during the search. If you unclick it before the search
finishes, the search will be suspended at the current phase.
The search results are displayed in the list on the left with the higher degree of similarity
to the searched spectrum at the top {the similarity degree is displayed in the
Rate
column).
While viewing the search results, the found spectra open as a second {red) curve.
Instead of search by a full spectrum, you can search by a part of it using the
Search
bandwidth
button. Clicking on it covers the spectral image with dark "curtains" that hide the
out of search spectrum sections. You can pick and move the curtains by dragging their edges.
Additional parameters are displayed in the
Search Settings
window that pops up after
you click the button with the same name. The
Spectrum
tab shows the maximum number of
the recordings to be selected and the minimum percentage of match rate. Peak positions and
heights to be considered are also set as a percentage of the maximum possible values. The
initial values are 85 and 25%, i.e. the peak positions are considered to a significantly greater
degree than their height, which helps identify spectra recorded under different conditions.
The
Acceleration
option involves all the CPU cores and multiplies the search speed almost by
the number of the cores. The
Reset to initial values
button restores the default values
applicable to ordinary tasks.
The other parameters under the tab refer to searching by mixtures. The command itself
is in the menu that drops down on clicking the side arrow to the right of the search button (in
other words, the button menu). Searching mixtures involves the ordinary search by spectrum.
The first entries of the search response, if their match rate is less than the preset value, are
searched again after substracting the spectrum from the query spectrum. As a rule, the preset
number of entries for a mixture search is smaller than that for an ordinary search (3–7) and
the rate is bigger {50–80%).
Note that a correct subtraction requires that the query spectrum be within the
absorption spectrum and reduced to it if it was in a different scale. Additionally, the spectrum
sections outside the absorption bands should be close to zero, otherwise the base line needs
adjustment. If it is not done manually, you should turn on the
Subtract base line
option. Note
that after an adjustment (including automatic) the spectrum is deemed changed and you will
be prompted to save the spectrum when closing it.
Turn on the
Only mixtures
option only in case you are sure that your sample is not a
pure substance. To eliminate results with single dominating substances, you can set the
minor component minimum content (the
Component
parameter).
Fig. 5 shows an example of mixture search for a mixture of two drugs. The search results
start with the spectra that are a linear combination of the library curves. Such an "artificial"
spectrum is marked with a"+" sign in front of the match rate. Click the sign to open the current
line for the other lines to display links to its substance components (the list on the left).
