For the Zetasizer Nano S or the Zetasizer Nano ZS instrument, the minimum concentration specification for size measurements is 0.1 ppm of 60 nm NIST traceable polystyrene latex and 0.1 mg/mL of a lysozyme solution. This article contains information about the experimental procedures and results achieved from measurements of a NIST traceable 60 nm polystyrene latex standard as well as from a 0.1 mg/mL lysozyme solution to demonstrate these minimum concentration limits.
- From the Thermo Scientific Duke Standards NIST traceable 3000 series (part number 3060A), 60 nm (diameter) polystyrene latex is supplied at a 1% w/v concentration
- Lysozyme from Fluka (catalog number 62970)
- 10 mM NaCl
- 100 mM KCl + 10 mM BisTris
- Syringe filters
- DTS0012 disposable sizing cuvettes
- Whatman Anotop 10 Plus 20 nm pore size filters (catalog number 6809–1102)
The 60 nm polystyrene latex standard was prepared in 10 mM NaCl at 0.1 ppm concentration.
Next, the lysozyme was prepared in 100 mM KCl with 10 mM BisTri solution at 0.1 mg/mL concentration. The resultant solution was filtered through the Whatman Anatop 20 nm pore size filter and the protein concentration was verified by measuring the absorbance at 280 nm on a UV/Vis spectrophotometer. The concentration was measured using an extinction coefficient of 26.4 m2/mol at a wavelength of 280 nm.
All measurements were taken at 25 °C.
Table 1 shows the results acquired from three repeat measurements of a 60 nm polystyrene latex in 10 mM NaCl at a concentration of 0.1 ppm. The table demonstrates the polydispersity index values and the z-average diameter (in nanometers) for each measurement, along with the standard and mean deviation values. Figure 1 depicts the intensity particle size distributions obtained from the measurements.
Table 1. Summary of the 3 repeat measurements of a traceable 60 nm polystyrene latex prepared at a 0.1 ppm concentration in 10 mM NaCl.
||z-Average Diameter (nm)
Figure 1. Intensity particle size distributions obtained from 3 repeat measurements of a traceable 60 nm polystyrene latex prepared at a 0.1 ppm concentration in 10 mM NaCl.
The polydispersity index values and z-average diameters are all within specification and the repeatability of the values gives assurance in the results obtained.
Figure 2 shows a plot of the mean size of peak 1 from the intensity particle size distributions acquired from measurements of lysozyme as a function of protein concentration. Each point demonstrates an error bar which is one standard deviation of a set of 5 repeat measurements. At 0.1 mg/mL, while the error in the measurement of size is more than at higher concentrations, the mean value is in the expected size range for lysozyme.
Figure 2. A plot of the mean size of peak 1 from the intensity particle size distributions obtained from measurements of lysozyme as a function of protein concentration.
At 0.1 mg/mL, the z-average size or cumulants analysis is not suitable as the baseline noise influences the calculated mean size, and this is more effectively explained using the largest peak from the protein distribution analysis.
In this article, the above results prove that the minimum concentration limit for size measurements with the Zetasizer Nano S and ZS instruments is 0.1 ppm and 0.1 mg/mL lysozyme.
This information has been sourced, reviewed and adapted from materials provided by Micromeritics Instrument Corporation.
For more information on this source, please visit Micromeritics Instrument Corporation.