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6.3.4. SEC
‘universal’
calibration
The effective hydrodynamic volume (volume per particle) can be expressed as
the product between the intrinsic viscosity (volume per gram) and the
molecular weight (gram per mol):
v
h
' = [
η
]M/
N
Avo
This is the basis for the so-called universal calibration. According to this
theory all polymers – irrespective of shape and extension – should follow the
same plot when log (
[η]
M) is plotted as a function of V. The theory has been
shown to hold for many synthetic polymers in organic solvents. For
biopolymers examples exist, but any tendency to non-specific (reversible)
adsorption (non-SEC mechanisms), which are quite common, makes this a
risky business and is not recommended, at least as a precise method.
In cases where the ‘universal calibration’ truly applies, the calibration can be
established on the basis of a single polymer system, for example dextran
standards (often used by biochemists). For another polymer, the peak position
(V) corresponds to a certain
[η]
M. If the intrinsic viscosity is measured
separately, M is obtained directly.