Converting Gradient Retention Times to Isocratic Retention Times in Reversed Phase Liquid Chromatography

Abstract

Various methods of converting gradient retention times in reversed phase liquid chromatography to isocratic retention times are compared. The two main methods investigated were the analytical solution to dV m = dV'/k, and the numerical solution to dV m = dV/(1+k). Other methods investigated involved using a quadratic expression for the dependence of log retention factor on mobile phase composition instead of the usual linear function and also inclusion of a correction for extra gradient delay due to void volume of the column. No method gave a good agreement between isocratic retention times estimated from gradient data and experimental isocratic retention times. The method which gave the best agreement was the numerical integration of dV m = dV/(1+k) using the usual linear relationship between log of retention factor and mobile phase composition. A modern spreadsheet was used for all calculations.