Static Light Scattering (SLS)
Absolute molecular weight measurement using light scattering.
Molecular weight can be measured using light scattering without the requirement for column calibration. In this technique the total amount of light scattered by the sample is measured by a sensitive detector at a particular scattering angle.
This technique is often called static light scattering or SLS.
The lack of calibration required means that the result is an absolute value, and Malvern Instruments provides two methods of performing this measurement for polymers and proteins in solution.
Size Exclusion chromatography detectors
Two scattering angles are available, and can be combined in a single detector using a single low-volume flow cell.
Right Angle Light Scattering, i.e. 90 degree light scattering (RALS) is optimal for small polymers and biological molecules such as proteins. This angle optimizes the sensitivity for these weakly scattering materials. Low Angle Light Scattering (LALS) is ideal for larger molecules such as polysaccharides and higher molecular weight polymers. The low angle means that the change in scattering as a function of angle does not have to be taken into account, and the molecular weight can be calculated directly.
Being combined with a separation technique enables the calculation of the absolute molecular weight at any point in the eluting chromatogram.
Batch measurement methods
Absolute molecular weight can also be determined by an experimental procedure using a cuvette based detector such as the Zetasizer µV, or one of the Zetasizer Nano series.
In this technique a Debye plot is constructed. This requires the measurement of the light scattered from a number of known concentrations of the analyte, followed by a linear extrapolation to determine the excess scattering at zero concentration.
As this is an ensemble technique, the result calculated is the weight average molecular weight of the sample measured.
Static Light Scattering products
- These systems measure:
- Zeta potential, particle size & molecular weight
- Particle size range:
- 0.3nm to 10µm
- Zeta potential size range:
- 0.38nm to 100µm
- Dispersion type:
- Dynamic light scattering, electrophoretic light scattering & static light scattering
- Equipment environment: