Waters ACQUITY UPC2, Overview And Maintenance Manual, Page: 63 / 84

Spectral contrast theory 59
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
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°.
Spectral contrast angle: 3.0°
Compound A
Compound B
Wavelength (nm)
Normali
zed abso
rb
ance