For the Zetasizer APS instrument, the minimum size specification (radius) is a peak mode of 0.3nm with a minimum size of 0.15nm. This technical note contains details of the experimental procedures and results obtained from measurements of sucrose solutions as demonstration of these minimum size specifications.
A 20% w/v solution of sucrose was prepared (20g of sucrose made up to 100g with deionized water) and the sample filtered through the 20nm pore-size filter into a suitable cuvette.
The measurements were taken at 25°C using a viscosity of 1.74mPa.s.
The intensity size distributions obtained from 3 repeat measurements of a 20% w/v sucrose solution are shown in figure 1 with the corresponding volume size distributions shown in figure 2. As described in the application note MRK1120, and the published paper MRK1034, the second peak in the intensity plot, and also seen as the 'bump' in the right of the correlation function (figure 3), is ascribed to collective diffusion of the sucrose molecules.
In terms of a volume distribution, there is only one peak with a mode of 0.6nm diameter as the larger peak is insignificant when the Mie transformation to volume is applied. This 0.6nm peak has a width with a distribution extending down to 0.3nm diameter (figure 4).
The overplot of the three correlation functions (figure 3) shows the repeatability of the data, which translates into the repeatability of the result.
The results reported in this technical note confirm that the minimum size capability (radius) of the Zetasizer APS is a peak mode of 0.3nm with a minimum size of 0.15nm.