Correction of anomalous covariance functions in low-angle quasi-elastic light scattering

The application of low-forward angle quasi-elastic light scattering to characterization of biological systems has been limited by maximal sensitivity of this approach to the transient presence of large Rayleigh or Mie scattering particles which contaminate the scattering volume. These particles result in anomalous autocovariance curves which translate to erroneous estimates of particle diffusion constants and Stokes radii. We have systematically considered two approaches to correct the cause of such anomalies before the autocorrelation step. This work has led to workable methods that allow low-angle quasi-elastic light scattering to provide reliable estimates of particle size. The approaches are useful in correcting errors due not only to 'dust' but also to more rapidly moving scatterers. To illustrate the method, bovine serum albumin and ovalbumin were used as example proteins.