Conformation and molecular weight distribution

Questions about Multi-Angle Light Scattering coupled with Size-Exclusion Chromatography or Field-Flow Fractionation

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Does conformation affect the molecular weight determination by MALS, and why? Do you assume that the protein/polymer must be spherically shaped? If not, how good is the fit with the MALS method?
The peptides, proteins or polymers do NOT need to be spherical for their molecular weight to be determined by MALS.

Molar mass is determined from the relationship between light scattering intensity, concentration and scattering angle. Regardless of conformation, the angular dependence of the intensity of scattered light P(θ) always approaches a value of one as the scattering angle θ approaches zero:


In MALS analysis, the data across multiple scattering angles is extrapolated to θ = 0 in order to determine the molecular weight accurately and with no dependence on conformation. For most proteins and smaller polymers, it is even easier: Rg/wavelength(lambda) is so small that extrapolation is not necessary, and P ~ 1 for all angles.

[answer provided by Vincent Hsieh, Ph.D., Wyatt Technology]
Daniel Some, Ph.D.
Principal Scientist
Wyatt Technology Corp.
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