Zetasizer APS Specifications DLS Minimum Size Limit

The Zetasizer APS, the minimum size specification (rad) is a peak mode of 0.3nm with a minimum size of 0.15nm. This note contains the method and results obtained from measurements of sucrose solutions to demonstrate these specifications

Introduction

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.

Experimental

Materials

  • Sucrose (food grade)
  • Deionized water
  • Whatman Anotop 10 syringe filters 20nm pore-size
  • Syringes
  • 96-well plate

Method

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.

Results

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.

Figure 1: Intensity size distributions obtained from 3 repeat measurements of 20% w/v sucrose solution
mrk1533 fig1
Figure 2: Volume size distributions obtained from 3 repeat measurements of 20% w/v sucrose solution
mrk1533 fig2

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).

Figure 3: Correlation functions obtained from 3 repeat measurements of 20% w/v sucrose solution
mrk1533 fig3
Figure 4: Volume size distributions obtained from 3 repeat measurements of 20% w/v sucrose solution
mrk1533 fig4

The overplot of the three correlation functions (figure 3) shows the repeatability of the data, which translates into the repeatability of the result.

Conclusions

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.

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