Comparison of isocratic and gradient elution reversed-phase behaviour of high-molecular-mass polystyrenes in dichloromethane and acetonitrile

Isocratic and gradient elution of high-molecular-mass polystyrenes were compared in a dichloromethane-acetonitrile mobile phase and C₁₈ bonded phase on a variety of different pore size silicas. Plots of the capacity factor versus the solvent composition were drawn from which solvent strength parameters, S, were determined for different molecular masses. Linear gradient elution data were also used to estimate S values using a graphical procedure. It was found that S depended on gradient rate and that only gradient rates of less than 2% /min gave constant values of S. Only molecular masses less than 50 000 gave good agreement with isocratic values. Plots of log S against log molecular mass were different for isocratic and gradient determined values of S.