Waters 2996, Operator'S Manual

Page: 68 / 84

46 Spectral Contrast Theory
5
Figure 5-4 Spectra with a Small Spectral Contrast Angle
Differences Between Spectra of the Same Compound
Small but significant differences between absorbance spectra can occur because of factors
other than those due to the absorbance properties of different compounds. For example,
multiple spectra of the same compound may exhibit slight differences because of detector
noise, photometric error, high sample concentration, or variations in solvent conditions.
The spectra in Figure 5-5, for example, show how instrument noise can affect the shape of
an absorbance spectrum of one compound. This effect is most likely to occur at low
concentrations where the signal-to-noise ratio is low. Note that the Spectral Contrast angle
between these absorbance spectra of the same compound is 3.4°.
N
orm
al
iz
ed
Abs
orb
anc
e
Wavelength (nm)
Compound A
Compound B
Spectral Contrast Angle: 3.0°