On-line coupling of flow field-flow fractionation and multi-angle laser light scattering

Abstract This paper describes the first successful coupling of a flow field-flow fractionator with a multi-angle laser light-scattering photometer in order to carry out absolute measurements of even high molar mass and radius of gyration distributions. Two standards with broad molar mass distributions, polystyrene particles and coil-shaped dissolved dextrans were investigated in order to establish the efficiency of this experimental apparatus. The distribution functions of molar mass and radius of gyration were determined for the samples. The results calculated for the dextran sample from the distribution functions were a weight-average molar mass of 2 730 000 g mol and a z-average radius of gyration of 47 nm. Comparison with results obtained from a conventional apparatus, consisting of size-exclusion chromatography and a light-scattering photometer, showed that field-flow fractionation is able to separate molecules in the range where size-exclusion chromatography fails owing to the existence of an exclusion boundary. The polystyrene latex sample gave results of 13 400 000 g mol for the weight-average molar mass and 15 nm for the z-average radius of gyration. In addition, a structure-property relationship in the form of an 〈R2G〉 1 2 versus M relationship was calculated for each substance. For the polystyrene latex standard in water an exponent of 0.33 ± 0.02 was found. The corresponding value for the dextran in 0.1 M sodium nitrate solution was 0.50 ± 0.01.

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