Correlation function analysis can be split into algorithms that only give the central moment and a measure of the width of the distribution (cumulants analysis (Koppel 1972)) and algorithms that attempt to model the complete particle size distribution by first deconvoluting the autocorrelation function using inverse Laplace transformation and then obtaining the central moment and dispersity from the modelled distribution, e.g. For the sake of simplicity, this algorithm will be further referred to as ‘frequency analysis’. 1992), which is based on the analysis of the power spectrum (the Fourier transform of the autocorrelation function), has been implemented by commercial manufacturers for evaluation in the frequency domain. Presently, only the algorithm outlined by Trainer and colleagues (Trainer et al. These algorithms can be grouped based on whether the evaluation of the measurement signal is performed in the time domain (correlation function analysis) or the frequency domain.
1992), but only a limited number have been implemented by commercial instrument manufacturers.
Many different mathematical algorithms to retrieve particle size and size distribution information from raw DLS data have been developed and proposed (Finsy et al. It is based on the analysis of the time-dependent fluctuations of intensity due to the interference between scattered and reference light caused by the Brownian motion of the light-scattering particles. The results also show that the conversion of intensity-weighted results to volume-weighted results increase the between-laboratory standard deviation, confirming the theoretical expectations that conversion increases the variation significantly.ĭynamic light scattering (DLS) has become one of the most widely used technique to determine the size of nanoparticles, mainly because of its rather simple and straightforward instrument operation and because it provides results within a short time. The results obtained from the cumulants method usually show the best repeatability and the lowest between-laboratory standard deviation. Also, precision, both within-laboratory (repeatability) as well as between-laboratory standard deviations (reproducibility), differs between the algorithms investigated, especially for the more polydisperse silica materials. The results show that the average particle diameters from different algorithms differ significantly and that these differences increase with an increasing polydispersity of the material. Particles have been measured in the size range of 10 to 200 nm. This assumption was tested using results obtained by cumulants analysis, CONTIN and Non-Negative Least Squares fitting (NNLS) of distributions, and frequency analysis on near-spherical silica and polystyrene latex particles obtained in one laboratory and results on near-spherical silica obtained in other laboratories. Users often implicitly assume that the various algorithms yield the same mean value and deliver results of the same precision. Different manufacturers of dynamic light scattering (DLS) instruments implement various evaluation algorithms.