Handbook of Size Exclusion Chromatography and Related ...

is often found in the literature when referring to the square root of the mean square
radius (r.m.s. radius).
From the theoretical summaries above, we see that light scattering
measurements and their interpretation depend simply on two fundamental
principles: 1) the intensity of light scattered by a sample is directly proportional to
the product of the molar mass and concentration (that is, measure the
concentration and then read off the molar mass!), and 2) the variation of the
scattered light intensity with angle is proportional to the molecules’ average size.
These are somewhat simplified versions of the following more exact statements.
1) The scattered light flux per unit solid angle about a direction u, in excess
of that scattered by the solvent, divided by the incident light intensity is directly
proportional to the product of the weight-average molar mass and the molecular
concentration. This means that R(u, c) / Mwc in the limit as c and u ! 0. 2) The
variation of scattered light flux with respect to sin 2 u=2 is directly proportional to
the average molecular mean-square radius in the limit as c and u ! 0.
Equivalently, dR(u, c)=d( sin 2 u=2) / kr2 gl in the limit as c and u ! 0.
A more detailed review of the theory and its interpretation may be found
in Ref. 14.
4 INSTRUMENTATION
Figure 1 is a schematic of the MALS measurement showing a light source
(generally a laser) producing a fine beam incident on the sample. The sample may
be contained in a cuvette of a flow cell. The scattered light from the sample is
collected over a range of angles with respect to the forward direction. Most MALS
measurements are made with light polarized perpendicular to the plane of
measurement. In recent years, solid-state lasers have replaced the formerly used
© 2004 by Marcel Dekker, Inc.
Figure 1 Schematic of an MALS measurement.