ENHANCED POLARIMETRIC DETECTION IN HPLC USING A REFRACTIVE-INDEX EQUALIZER

Pseudorotation effects in polarimetric detectors for HPLC are investig ated, and a method to actively reduce these distortions is presented. In this method, the refractive index of the eluents is maintained at a constant value by mixing a variable amount of a second, optically den ser phase. To do this, a detector measures the refractive index of the eluents and its signal is fed back to control the pumping rate of the second phase. To demonstrate the method, a prototype instrument using a refractive index detector with a detection volume of 0.1 mu L was c onstructed. It had a total dead volume of 3 mu L and made possible the suppression of refractive index peaks as small as 60 mu L. This instr ument was used to improve the accuracy of a commercial polarimetric de tector in the determination of the enantiomeric excess of (R,S)-1-phen ylethanol samples by canceling the pseudorotation.