Laser-based optical activity detector for high performance liquid chromatography
The identification of chromatographic peaks is simplified when multiple detectors are used, particularly those that monitor entirely different physical properties. A concept that has recently been demonstrated is detection based on the rotation of polarized light by optically active molecules. One can make use of the presence or absence of optical activity, the sign of the optical rotation, as well as the wavelength dependence of the rotation, to aid in the identification of peaks. The working system is based on the use of a laser and high quality optics. A detection limit approaching that of the conventional UV absorption detector can be achieved in a small volume flow cell. Three specific applications will be discussed. In human urine, the determination of various sugars, except glucose, has been a problem. The detector based on optical activity is ideal in this case. The other optically active components can be separated by the use of a heavy-metal ion exchange column. In human plasma, the determination of the lipid profile is of interest. While some success has been reported using far UV absorption, interference between triglycerides and free cholesterol is a problem. Furthermore, important species like cholestanol has no convenient absorption bands. The optical activity detector once again can be used to overcome these problems;Also, chromatograms are obtained for various saturated fractions of shale oil, having different particle sizes and from different sources. Separation is accomplished by reversed-phase high performance liquid chromatography and the eluate is monitored by the optical activity detector. The chromatograms show an abundance of optically active components, which may be good fingerprints for the various shale oils.