Retention behaviour of amylopectins in asymmetrical flow field-flow fractionation studied by multi-angle light scattering detection

Asymmetrical flow field-flow fractionation (FFF) with multi-angle light sca ttering (MALS) detection was applied for the fractionation of amylopectins from four different sources. Samples originated from genetically modified p otatoes and waxy maize. Amylopectins were dissolved in a I mol l(-1) sodium hydroxide solution or water. With an injected mass of 0.2 mug, well below overloading conditions, a decrease of the apparent hydrodynamic radius with increasing inlet flow-rate was observed. Moreover, a decrease of the radiu s of gyration with increasing elution volume was recorded by the MALS detec tor. Steric/hyperlayer effects are a feasible explanation for this behaviou r. The observed radius of gyration at the steric inversion point was in the order of 0.3 mum, which is smaller than the theoretically calculated inver sion point. Apparently, the amylopectin behave as macromolecules with a lar ger hydrodynamic radius than expected on basis of their radius of gyration and are subjected to significant lift forces. The results were confirmed by four fractionations with varying flow-rates but constant ratio of cross to outlet-flow. In contrast to the normal mode operation, the retention of th e amylopectins depended strongly on the applied flow-rates and was close to that of a much smaller 10 kDa dextran. Apparent molar masses in the order of between 10(7) and 10(9) g mol(-1) were obtained. The results are contras ted with enzymatically degraded and oxidised starch samples that were fract ionated in the normal mode. (C) 2001 Elsevier Science B.V. All fights reser ved.