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]