Polarimetric Detection in Liquid Chromatography: An Approach to Correct Refractive Index Artefacts

Abstract

The study of factors influencing the quality of polarimetric signals from chromatographic analysis of mixtures of enantiomers shows that changes in refraction index of mobile phase, analyte concentration, and flow rate of mobile phase can give unacceptable errors that preclude polarimetric measurements to be used in enantiomeric purity determinations. Although, recent advances in polarimetric detectors (enhancing S/N ratio) avoid, in part, this effect, errors arising from quantitative measurements and calibration functions when analyzing compounds having small specific rotations or/and mixtures with small enantiomeric excess may be serious and must be corrected. In this paper, a simple equation was derived to correct deviations arising from refractive index artefacts (RIA effect), effectively useful in mixtures of enantiomers closest to racemic composition and at the extreme of the scale. Styrene glycol and citramalic acid enantiomers were used as examples of the efficacy of the approach to correct the RIA effect.

Keywords:

• Calibration factor
• Enantiomeric excess
• Liquid chromatography
• Polarimetric detection
• Ria effect

ACKNOWLEDGMENT

Contract Grant sponsor: Ministerio de Ciencia y Tecnologia of the Spanish Government. Contract Grant number: CTQ04–07778.

Notes

All signals were plotted against m (µg).