COMPARISON OF THEORETICAL METHODS FOR EXTRACTING RETENTION FACTORS AND RATE CONSTANTS IN LIQUID CHROMATOGRAPHY

Abstract

In this research, experimental data are used to evaluate theoretical methods that provide detailed information concerning mass transfer processes in liquid chromatography. To this end, a well-characterized homologous series of fatty acids is separated on a polymeric octadecyl silica stationary phase with a methanol mobile phase. These solutes are detected via laser-induced fluorescence to generate characteristic zone profiles as a function of column length and linear velocity. Three theoretical methods are then applied to extract the thermodynamic and kinetic information from the zone profiles. Each method relies on evaluating the shape of the zone profiles. The statistical moments of the profiles are used to calculate the mean and variance, which are related to the retention factor and rate constant, respectively. The profiles are also fit to the exponentially modified Gaussian equation and the Thomas equation. The fitting parameters from these equations are then used to calculate the retention factors and rate constants. These methods are compared and their inherent advantages and limitations are discussed.

Keywords:

• exponentially modified Gaussian function
• kinetic rate constants
• liquid chromatography
• retention factor
• statistical moments
• Thomas model

ACKNOWLEDGMENTS

The authors thank Dr. Lane C. Sander (National Institute of Standards and Technology) for synthesis of the polymeric octadecyl silica stationary phase and Dr. Shu-Hui Chen for derivatization of the fatty acids.

Notes

^a Values for all other parameters (A, B_m, B_s) as given in text.

^a Values for all other parameters (A, B_m, B_s) as given in text.

^a Values for all other parameters (A, B_m, B_s) as given in text.