Displaying and Using UV Spectra
Match Factor, Difference Spectra, 1st/2nd Derivatives of Spectra

When two or more spectra are represented on the spectra plot, the similarity of the UV spectra becomes an issue.

The match factor can express the similarity, by forming difference spectra or by representing the first or second derivative of a UV spectrum.

• Select Decorations on the View or context menu and select the Show match check box on the Label tab page. Chromeleon issues a value for each represented spectrum, expressing the match degree relative to the main spectrum (0 = no match; 1000 = perfect match).

• On the Analysis tab, define whether the difference spectrum or the first or second derivative of a spectrum is displayed in a second window in addition to the actual spectra.

In the case of the match factor and the difference spectrum, the question which UV spectrum is considered a main spectrum is especially important, as this is the basis of comparison or the basis for all calculations.

Usually, this is the peak spectrum extracted at the retention time. If there is no peak spectrum, distinguish two situations: If you select the Spectra/I-t Plots Tool to extract the single UV spectra from the chromatogram, the first spectrum that is extracted is the main spectrum. If spectra are extracted automatically at different peak heights, the spectrum with the "oldest" retention time is considered the main spectrum. When representing difference spectra, the Difference to entry indicates the basis of calculation.