Ionomer and protein size analysis by analytical ultracentrifugation and electrospray scanning mobility particle sizer.

By combining analytical ultracentrifugation (AUC) in liquid phase and scanning mobility particle sizer (SMPS) in the gas phase, additional information on the particle size and morphology has been obtained for rigid particles. In this paper, we transfer this concept to soft particles, allowing us to analyze the size and molar mass of the short side chain perfluorosulfonic acid ionomer Aquivion® in a dilute aqueous suspension. The determination of the primary size and exact molar mass of this class of polymers is challenging since they are optically transparent and due to the formation of different aggregate structures depending on the concentration and solvent properties. First, validation of AUC and SMPS measurements was carried out using the well-defined biopolymers bovine serum albumin (BSA) and lysozyme (LYZ) to confirm the reliability of the results of the two unique and independent classifying methods. Then, the ionomer Aquivion® was studied using both techniques. From the mean molar mass of 185 ± 14 kDa obtained by AUC, a mean hydrodynamic diameter of 7.6 ± 0.5 nm was calculated. The particle size obtained from SMPS (7.1 nm) agrees very well with the results from AUC showing that the molecule was transferred into the gas phase without significantly changing its structure. In conclusion, the Aquivion® is molecularly dispersed in the used aqueous buffer solution without any aggregate formation in the investigated concentration range (< 2 g l-1).