Concentration effects and thermodynamic nonideality in gel chromatography

The dependence of the elution volume Ve on the concentration of injected polymer c in gel chromatography is presented for several systems including poly(styrene) and poly(methyl methacrylate) in a number of pure solvents with SiO2‐based gels. The linear dependence of Ve on c and Kav on c (where Kav is the distribution coefficient) is confirmed in the region of very low concentration. The slopes k of the straight lines increase with increasing relative molecular masses M of the polymer injected and with increasing thermodynamic nonideality of the system (as expressed by the second virial coefficient A2). The significance of the slope of the GPC calibration curve for meaningful comparison of the concentration effects in various chromatographic systems is pointed out. A recently found correlation between k and (A2M)γ is confirmed with a γ value of about 0.8. A possible theoretical explanation for the deviation of γ from unity is discussed. Finally, the influence of both the polymer concentration and the thermodynamic quality of the eluent on the resolution index of the chromatographic system is evaluated with the conclusion that thermodynamically poor solvents should be preferred for preparative GPC separations with very high loads.