The scattering of light from dilute polymer solutions is based on classical or Rayleigh light scattering, named after Lord Rayleigh III (1842–1919), who had discovered that the intensity of light scattered by small particles in air is proportional to the 4th-power of the wavelength of the incident light (1). The only required parameters that must be known beforehand are the refractive index of the mobile phase and the specific refractive index of the polymer solution, two easily measured quantities. Moreover, molecular size (radius of gyration) can also be obtained. This method requires no column calibration because the relationship between the intensity of scattered light and molecular weight is based on first principles. When primary polymer standards are unavailable, the most reliable way to obtain accurate molecular weight data from SEC is the use of light scattering detection. Regardless of the procedure used, columns still require frequent calibration to correct for flow rate drift and column deterioration. Also, these procedures assume that universal calibration is valid for samples that are being analyzed. For improved accuracy, universal calibration can be utilized with online viscometry nevertheless, calibration with secondary standards is still required.

Alternatively, although less reliable, universal calibration can be employed using secondary standards however, Mark-Houwink coefficients of both the sample and secondary standards used for column calibration must be known.

To obtain accurate results, columns must be calibrated with primary standards that are chemically and structurally equivalent to samples being analyzed. Size-exclusion chromatography (SEC) is used primarily for determining the molecular weight distribution and statistical molecular weight averages of polymeric samples.

Light scattering intensity equation