Representing Spectra As Vectors - Waters ACQUITY UPLC Operator's, Overview And Maintenance Manual

Comparing spectra of two compounds
0.40
0.20
0.00
344.5063 nm, 0.4595 AU

Representing spectra as vectors

The spectral contrast algorithm uses vectors to quantify differences in the
shapes of spectra, converting baseline-corrected spectra to vectors and then
comparing the vectors. Spectral vectors have two properties:
• Length – Proportional to analyte concentration.
• Direction – Determined by the relative absorbance of the analyte at all
wavelengths (its absorbance spectrum). Direction is independent of
concentration for peaks that are less than 1.0 AU across the collected
wavelength range.
Vector direction contributes to the identification of a compound, since the
direction is a function of the absorbance compound's spectrum. The ability of
spectral vectors to differentiate compounds depends on the resolution of
spectral features. As both wavelength range and spectral resolution increase,
the precision of a spectral vector for the resultant spectrum increases. A
detector-derived vector can include absorbances in the range of 190 to 500 nm.
To enhance spectral sensitivity, set the bench resolution to 1.2 nm.
62
245 nm
257 nm
Compound A
220.00 240.00 260.00
Compound A:
Compound B:
Compound B
280.00 300.00 320.00
nm
Ab
245
-------------- - = 2.2
Ab
257
Ab
245
-------------- - = 0.7
Ab
257
340.00