Waters ACQUITY UPLC Operator's, Overview And Maintenance Manual page 78

Spectra with a small spectral contrast angle
Spectral contrast angle: 3.0°
Compound A
Compound B
Wavelength (nm)
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
the next figure, 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°.
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