Nonlinear retention relationships in reversed-phase chromatography

Recent experimental studies of retention and selectivity patterns of different reversed-phase columns demonstrated that the commonly used assumption of a linear relationship between the logarithm of the retention factor and the solvent composition is a simplification. Due to the difficulties associated with this assumption, a new simple equation was developed that permits the description of curvature in this relationship. The equation can be integrated and used as a general model for the interpretation of retention data in gradient chromatography. In this paper, we present the new equation and discuss its implications in detail, including a few examples where it serves better than the classical linear equation.