Typical online PLSanalysis of the sulfur concentrations. The plot shows Raman predicted values vs. the measured laboratory values. The standard error of prediction for the PLS model with outliers removed was 2.45 ppm.
A histogram of the distribution of differences between the laboratory and Raman predictions for an independent validation set of spectra that are not included in the PLS model. The standard error of prediction for the validation set (370 samples) with 3 outliers removed was 3.09 ppm.
An ad hoc trend of total sulfur measurements comparing online Raman with online UV fluorescence. Excellent agreement is observed with the two different techniques.