Asymmetrical flow field-flow fractionation coupled with multi-angle light scattering and refractive index detections for characterization of ultra-high molar mass poly(acrylamide) flocculants

The molar mass distributions of ultra-high molar mass polyacrylamide-based flocculants were measured using asymmetrical flow field-flow fractionation (AFFFF) coupled with multi-angle light scattering and refractive index detectors. The mass load onto the separation channel was found to be critical in obtaining a good size separation. The detailed investigation with ultra-high molar mass polyacrylamides found that the injected amount should be ≤1 μg to ensure separation according to AFFFF mechanism. As a consequence of the limited sample mass load, the signal-to-noise ratio (S/N) of the detector responses was low. To overcome this limitation and thereby to obtain more accurate and precise molar mass and radius information, each sample was injected 10 times and the resulting signals were averaged before calculating the molar mass and radius. In addition, the channel was equipped with a slotted outlet to increase the concentration of sample passing through the detectors. After implementing the above strategies, it was possible to perform separation of polymers having molar mass and size as high as 108 g mol−1 and root-mean-square radius of ∼250 nm, respectively. The resulting weight-average molar mass of the highest MW sample was in excess of 18 × 106 g mol−1.