OPTIMIZED CALIBRATION CURVE FOR SIZE-EXCLUSION CHROMATOGRAPHY APPLIEDTO POLY(VINYL CHLORIDE)

The problem of using a polystyrene-standard-based calibration curve fo r other polymers has been overcome by developing an algorithm based on the concept of parameter estimation and optimization. The algorithm m odifies the regression coefficients of the polystyrene-standard-based calibration curve by interactively using the chromatographic output an d the absolute number-average molecular weight of the experimental pol ymer. Analytical expressions have been derived for calculating the dir ectional derivatives, which ensure rapid convergence of the objective function. The algorithm, applied to commercial poly(vinyl chloride), o ffered a number-average molecular weight of 32 037 whereas that measur ed by membrane osmometry is 32 000. The polymer characterization param eters calculated from the optimized calibration curve closely matched those obtained from the universal calibration curve and Q-factor value s. The algorithm needs no narrow standard of the experimental polymer, and holds for homopolymers, copolymers and polymer blends. It can be easily incorporated into commercial size exclusion chromatography data -reduction software packages.