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

Converting
spectra to their first
or second derivatives
The first derivative
Use Derivative in the Process menu to convert the selected spectra to their first or
second derivatives. The first derivative is useful for revealing peaks that appear as
shoulders in the original spectra. Use the second derivative to find the exact
location (center) of shoulders in the original spectra.
The original spectra can be in any units when you use Derivative; however, the
derivative operation is usually applied to absorbance, Kubelka-Munk or
photoacoustic spectra.
The first derivative shows the rate of change across the entire spectrum. This means
that in the first derivative, shoulders become narrower and thus are easier to see. It is
important to remember that the maximum and minimum and minimum points in the
first derivative curve are the points of maximum rate of change and not the
maximum and minimum points of the original peaks. The maximum and minimum
points of the original peaks have a Y value of zero in the first derivative.
The following illustration shows a spectrum with the first derivative above it.
The second derivative
The second derivative shows the change in the rate of change across the spectrum.
This curve is more complex than the first derivative, with significantly narrower
bands. The second derivative is useful for finding exact peak locations since peaks
in the second derivative appear at the same locations as peaks in the original
spectrum.
The following example shows a spectrum with the first derivative above it and the
second derivative at the top.
222 Thermo Nicolet