Data Reduction in Multidetector Size Exclusion Chromatography

Abstract

A comprehensive analysis of multidetector size exclusion chromatography (SEC) is presented. The system examined consists of differential refractometer, capillary viscometer, and light-scattering detector combination. New approaches for interpreting multidetector data have been developed. The first one consists in eliminating the concentration chromatogram from the data reduction process. The traces of two molecular-weight-sensitive detectors alone allow calculating molecular weight and intrinsic viscosity distributions of an unknown polymer, assuming the validity of the universal calibration concept for this polymer. This approach can dramatically improve the characterization of polymers with long high-molecular-weight tails, when small amounts of high-molecular-weight fractions are detected by the light-scattering and viscometer detectors, but the concentration is too low to be registered by the refractometer.

Another opportunity discovered is the calculation of the hydrodynamic volume of each fraction of a chromatographed polymer across its distribution, using measured signals from three on-line detectors. This calculation can be performed for any complex polymers, e.g., copolymers or oligomers, even in situations when refractive index increments of molecules depend on retention volume, or columns do not provide full recovery of injected polymer mass. The verification of the universal calibration hypothesis for any unknown polymer is accomplished now by the routine single chromatographic run. The method developed helps to analyze different reasons responsible for the deviation from universal calibration, such as polymer-polymer interactions in solution, band-broadening phenomena, non-steric interactions with a stationary phase or the structural or chemical heterogeneity of a solute. Using triple detection with multiangle light-scattering detector allows, also, to calculate the Flory's viscosity factor across the distribution for polymers with different configurational and conformational structure. The experimental data supporting the theoretical predictions are presented.