Peak® Classical Least Squares (CLS)
CLS is often used for the analysis of complex mixtures of gases (vapor phase samples), for instance combustion processes. CLS requires spectra of pure compounds of known concentrations, known as a 'standard' or 'calibration' spectrum. In some cases you may need only one standard for a given compound, if the concentration vs. absorbance curve is linear. Often, however, the absorbance will fall off at higher concentrations, so the calibration curve is not linear. In this case, for a more accurate measurement, it is necessary to provide more calibration spectra at a range of concentrations.
Peak® Spectroscopy Software's CLS implementation is based on the 'multi-band weighting' technique combined with standard-bracketed interpolation, providing robust and sensitive concentration measurements.
A manual is available here: Peak_CLS.pdf
The C3F8 CLS method referenced in the manual can be downloaded: c3f8_cls_method.zip