Solvent modulation in liquid chromatography: general concept and theory

Abstract

A novel solvent delivery method, called solvent modulation, Is described as an alternative to premixed mobile phases in liquid chromatography. In solvent modulation, Individual solvent zones are Introduced onto the chromatographic column In a varying or repeating sequence. Because the solvents are of constant composition and the zones are spatially separated from one another, solute retention should be controlled Independently In each zone. Thus, the overall retention of the solute Is a readily predictable, linear combination of the capacity factors In the Individual solvent zones It encounters. In this paper, the general concept and theory of solute retention are developed and possible deviations from Ideal behavior are discussed. The extent of solvent zone dispersion by the chromatographic column, and the resulting imprecision In solvent zone length, Is shown to be a primary contribution to Imprecision In solute retention. Based on this Inherent limitation, the experimental conditions suitable for solvent modulation are examined. Under these conditions, solvent modulation is shown to offer a simple, versatile, and accurately modeled means to control and predict solute retention.

Parametric Modulation in Liquid Chromatography: Multivariate Optimization of Mobile Phase Composition and Temperature

“…To overcome this problem, a new approach has been developed for univariate and multivariate optimization called parametric modulation. ,− The fundamental strategy of this approach is that chromatographic retention may be accurately predicted if the solute is constrained to undergo interactions independently within each environment of mobile phase, stationary phase, temperature, etc. This strategy is implemented by maintaining each of these parameters in discrete and separate zones along the chromatographic column, as illustrated schematically for modulation of mobile phase and temperature in Figure .…”