Accuracy in Multiangle Light Scattering Measurements for Molar Mass and Radius Estimations. Model Calculations and Experiments

Abstract

Multiangle light scattering (MALS) is a well-established technique used to determine the size of macromolecules and particles. In this study, different extrapolation procedures used in MALS were investigated with regard to accuracy and robustness in the obtained molar mass and rms radius. Three different mathematical transformations of the light scattering function referred to as the Debye, Zimm, and Berry methods for constructing the Debye plot were investigated for two idealized polymer shapes, homogeneous spheres and random coils, with radii from 25 to 250 nm. The effect of the angular interval used for the extrapolation was investigated, as was the robustness of the different transformations toward errors in the measured light scattering intensity at low angles. For an rms radius less than 50 nm, the relative error in molar mass due to extrapolation was less than 1% independent of the method used. For larger radii, the error increased and the extrapolation procedure became more critical. For random coil polymers, the Berry method was superior in terms of accuracy and robustness. For spheres, the Debye method was superior. The Zimm method was inferior to the others. The different extrapolation methods were evaluated and compared on experimental data from a size exclusion chromatography-MALS analysis of an ultrahigh molar mass poly(ethylene oxide) (PEO). The PEO data qualitatively verified the calculations and stressed the importance of optimizing the extrapolation procedure after careful evaluation of the experimental data. A discussion of how to detect erroneous data in an experimental Debye plot is given.

Size Separation Techniques for the Characterisation of Cross-Linked Casein: A Review of Methods and Their Applications

“…The light scattering data obtained from MALS can be fitted by different approaches, the most prominent one represented by the Zimm equation, allowing the evaluation of both M W and R g . With respect to the type of the macromolecules, different models have been developed for fitting the light scattering data [199].…”

Rheological properties of a polysaccharide isolated from Adansonia digitata leaves

“…The value of the parameter ν gives information about the conformation of the polysaccharide macromolecules. It has a value of 0.33 for spheres and 0.5-0.6 for random coils (Andersson, Wittgren, & Wahlund, 2003). Figure 1b shows the conformation plot for Adansonia digitata polysaccharide in aqueous solution.…”

Quantitative analysis of virus‐like particle size and distribution by field‐flow fractionation

“…Astra V software (version 5.3.1.5, Wyatt Technology Corporation) was used for data acquisition and correction for both inter-detector delay and band broadening. Algorithm used by the software for calculation of r.m.s radii was has been described (Sun, 2004;Tanford, 1961;Wyatt, 1993) and uses the Zimm fitting method (Andersson et al, 2003). HPLC grade toluene filtered through 0.02 mm Anotope filters (Whatman, Middlesex, UK) was used to calibrate the MALS system.…”