Gel permeation chromatography. II. Molecular size separability and the determination of polymer polydispersity

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Abstract
An equation describing the relationship between the GPC determined breadth of the molecular weight distribution, (σn/Mn)G, the true breadth of the distribution, σn/Mn, zone spreading or tailing ΔVe, and the separability employed, K(M), has been derived: magnified image .Here K(M) is the absolute value of the derivative dVe/dM, in which Ve is elution volume and M is molecular weight. The validity of this equation was established through GPC fractionations of blends of narrow molecular weight distribution polystyrenes. Application of the equation to experimental data shows that ΔVe increases with increasing M. The equation indicates that GPC molecular weight data are less in error with polymers of broader molecular weight distributions and with larger values of K(M). The importance of the experimental variable K(M) is that it defines the degree of fractionation, higher values of K(M) denoting more complete fractionation.