Handbook of Size Exclusion Chromatography and Related ...

educed viscosity, h r, to be computed at each instant, without any calibration
factor, according to
h r(t) ¼
V(t) V(0)
V(0)c(t)
The intrinsic viscosity [h] is related to h r according to
h r ¼ [h] þ kH[h] 2 c þ kH,2c 2 þ O(c 3 ) (6)
where kH is 0:4 for neutral polymers, and kH,2 has no generally accepted
theoretical form for coil polymers, although empirical expressions exist (30). [h]
measures the hydrodynamic volume VH, per unit mass according to
[h] ¼ 5VH
2M
Shear rates in the capillary viscometer were of the order 500s 1 .
1.3 Heterogeneous Time-Dependent Static Light Scattering
(HTDSLS)
Recently, HTDSLS was introduced as a detection and analysis technique, in order
to permit the simultaneous characterization of solutions containing co-existing
populations of polymers and colloids (31). Such solutions occur in many contexts:
(1) bacteria that produce or degrade natural products, such as proteins and
polysaccharides, (2) microgels and microcrystals that form inside polymer
reaction solutions, aggregates of proteins, and other polymers in otherwise
homogeneous solutions, (3) solutions containing “dust” and other optical
contaminants that would normally have rendered the solution uncharacterizable by
classical light-scattering techniques. Other scenarios also exist.
The main notion of HTDSLS is to make a very small scattering volume Vs
(of the order of nanoliters, as opposed to the total sample volume, which is
typically tens of microliters) and to use a flowing sample, so that each time a
colloid particle passes through the scattering volume a large scattering spike is
produced. It has been shown (31) that the “clear window time,” CWT, that is, the
fraction of time no large scatterers are in the illuminated scattering volume, has the
limiting form
(5)
(7)
CWT ffi exp( nVs) (8)
where n is the number density of large particles. In the meantime, the average
scattering level within the scattering volume is a result of the polymeric
population. Built-in algorithms then allow for discriminating and counting the
spikes due to colloids, while simultaneously measuring the baseline scattering due
to the polymer. Thus, absolute molecular mass and size characterization, and its
© 2004 by Marcel Dekker, Inc.