Theoretical consideration on polarized photometric detection

Previously, we developed a novel detector, a polarized photometric detector for optically active compounds, where two polarizers are set on either side of the UV-visible absorbance detector flow cell. In this paper, we present theoretical considerations on this method with several equations. If the inclined angle of the second polarizer is defined as alpha (left when alpha > 0 degree), the following equation is obtained: delta Abs = 2 log e.tan alpha.beta, where delta Abs is the change in absorbance and beta (magnitude of beta << alpha) is the angle of rotation of light passing through the cell containing the optically active compound. This equation suggests that delta Abs is proportional to the analyte concentration and that the dextro- and laevorotatory compounds are detected as positive and negative absorbance changes, respectively. The theoretical maximum signal to noise (S/N) ratio is obtained when alpha = 45 degrees (= 0.8 rad) and the smallest detection limit is 5 x 10(-5) degrees (S/N = 3) when the path length of the flow cell is 10 mm. This detector was successfully used in flow injection analysis (FIA) as well as HPLC for optically active compounds.