Light scattering has become one of the most important techniques for the characterization of macromolecules and nanoparticles in solution. Depending on the analytes, different light scattering techniques can or have to be used. When compared to many other characterization methods, the light scattering techniques show a high precision, have a fast response time and are noninvasive. Once the light scattering technique is set-up properly, absolute measurements of molar mass and particles size can be performed without the use of standards. Beside Laser Diffraction, the most commonly used light scattering techniques are Static Light Scattering (SLS) and Dynamic Light Scattering (DLS):
Light scattering can be done in Batch Mode and or in Flow Mode. Batch Mode analysis is easy to perform, but in case of crude complex sample mixtures with a broad and or multi-modal distribution, this approach has significant limitations, as it is difficult to calculate the correct molar mass and particle size distribution with light scattering only. A solution to overcome this limitation is the combination of a separation technique, such as Field-Flow Fractionation or Chromatography, with online light scattering detection (Flow Mode). Field-Flow Fractionation and Size Exclusion Chromatography provide high resolution fractions of the polymers/particles under investigation. After the separation, the eluting monodisperse sample fractions can be ideally sized online by light scattering. Thus the combination of a separation technique and a light scattering detection technique provides a very powerful characterization tool, which exceeds the performance of the single separation or the single detection technology when used alone. An additionally advantage is that sample fractions can be recovered for further subsequent analysis with other techniques after leaving the detector.
The scientific attractiveness of light scattering is based on the unique
combination of high sensitivity, high resolution, easy handling and fast
analysis times. Other techniques, which can be seen more as complementary
than competing, are Analytical Ultracentrifugation, Mass Spectroscopy and
membrane Osmometry. Analytical Ultracentrifugation for example shows high
resolution, but is much more expensive and complicated and has longer run
times. Mass Spectroscopy has become very famous in the last decade, but this
technique also requires a big investment and does not reach the same upper
molar mass range as light scattering does. Membrane Osmometry is another
suitable technique, but it is not possible to use this technology as online
detector and the resolution and molar mass range is much more restricted
than what can be expected from light scattering.