Dependence of the capacity ratio on the composition of the mobile phase in liquid adsorption chromatography

Abstract

In order to investigate the effects of multicomponent mobile phase on liquid adsorption chromatographic separation, a LSC retention of solute molecules was modeled for the binary and ternary mobile phase systems using Snyder``s theory. From this simple model involving solute-solvent interactions, the relationship between sample capacity ratio and mobile phase composition was derived. The relationship for binary mobile phase system between the reciprocal of sample capacity ratio and the mobile phase composition was described by a simple second order equation. $$1/K``_b = a_bx_c^o + b_bx_c^{o^2}$$ For the analysis of ternary mobile phase system, the iso-line method was used. The relationship between the reciprocal of sample capacity ratio and the mobile phase composition was expressed as $$1/K``_t = a_{tA} + b_{tA}x_c^o + c_{tA}x_c^{o^2}$$ for constant mole fraction of diluent. $$1/K``_t = a_{tB} + b_{tB} + c_{tB}x_c^{o^2}$$ for constant mole fraction of semi-polar solvent. $$1/K``_t = a_{tC}+ b_{tC}x_B^o$$ and for constant mole fraction of polar solvent. The experimental results which obtained for the binary and for the ternary mobile phase systems were well fitted to the theoretical model equations. Although the experimental results for the ternary mobile phase system show a nonideality of solution, each coefficient in the equation could be seen as constant for each curve which obtained by iso-line method. The capacity ratio of the sample having short retention time was affected largely by the mobile phase composition. While the sample retention was affected largely when a mobile phase was polar. Form the result for the variations of mobile phase flow rate, the sample retention time decreased as the mobile phase flow rate increased, but the sample capacity ratio remained constant upon the mobile phase flow rate.