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Threshold angle
In addition to computing spectral contrast angles, the spectral contrast
algorithm also computes a threshold angle. The threshold angle is the
maximum spectral contrast angle between spectra that can be attributed to
nonideal phenomena.
Comparison of a spectral contrast angle to its threshold angle can help
determine whether the shape difference between spectra is genuine. In
general, a spectral contrast angle less than its threshold angle indicates that
shape differences are attributable to nonideal phenomena alone and that no
evidence exists for genuine differences between the spectra. A spectral
contrast angle greater than its threshold angle indicates that the shape
differences arise from genuine differences between the spectra. When
automating the spectral contrast comparison, the maximum absorbance of the
spectra must not exceed 1 AU.
Effects of pH on the absorbance spectrum of p -aminobenzoic acid:
Effect of pH
pH 6.9
pH 5.1
pH 3.1
Wavelength (nm)
Abso
rbance