An optical rotation detector can be used for selective detection of optically active materials.
The sugar in black and lemon teas were analyzed using a combination of optical rotation detector (OR) and refractive index detector (RI).
Figure 1 Chromatogram of a standard sample. Meso-erythritol is optically inactive and can only be detected by refractive index.
Figure 2 chromatograms of sugar-free black tea and lemon tea.
Figure 2, Limonene and Carvone have very similar UV spectra, but show differences in the IR. Co-elution in the chromatogram detected using UV as shown in figure 3 and 4 illustrates the inability of using UV to trigger fraction collection.
Figure 5 shows IR chromatograms at two different wave number ranges and the fractions collected using those chromatograms. A Carvone standard and Spearmint oil were separated using HPLC and fractions 1 and 2 were compared to confirm the separation and purity as seen in Figure 6.