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Abstract

The determination of continuous size distributions from dynamic light scattering measurements requires data of extremely high accuracy. The ill-conditioned nature of the inversion of experimental data is illustrated. It is shown that large differences in size distributions are only poorly expressed by the corresponding autocorrelation functions and thus difficult to extract, even from relatively low noise data. A high statistical accuracy of data is a prerequisite, but often may not suffice. It is demonstrated with data of high statistical accuracy from calibrated polystyrene latex particles that baseline errors of less than 0.1% ca distort the resulting size distribution and mimic non-existent side peaks. Using a new method, where the characteristics of normalization errors are incorporated into the inversion algorithm, and which fits for the relative baseline error as additional parameter, these distortions can be avoided. This technique is applied to determine size distribution of phospholipid vesicles prepared by gel filtration and sonication using a newly synthesized phospholipid. The results indicate that both methods yield small vesicles of essentially the same size, the average radius of which is about 10 nm. In a second application, two stages of a crystallization experiment are investigated with dynamic light scattering and electron microscopy and the results compared. There is a very good agreement in the particle sizes determined from the two methods, which confirms the ability of the extended inversion algorithm to provide stable and reliable solutions, and hence also to discern fine details of such particulate suspensions.