Zetasizer Blue Sensitivity – how much polymer?

Recently, we published a blog on Zetasizer red sensitivity. That post was specifically for the Zetasizer Red series. So how about the Blue series? What are the minimum polymer concentration requirements for the Zetasizer Blue? Therefore, let’s discuss the Zetasizer blue sensitivity of the Zetasizer Advance series.

What impacts light scattering sensitivity?

Light scattering systems have varying sensitivity levels. The main apparent influences are:

• overall optical setup efficiency (detection angle, fiber optics or pinholes, optical filters, detection losses).
• detector sensitivity or detection efficiency (avalanche photo diode detector or photo multiplier tube, quantum efficiency at specific wave length).
• laser source (wave length, beam quality, divergence, TEM00 mode Gaussian profile, output power).

In the Zetasizer Advance series, the first two points are equal for the respective model variants. For example, the red Ultra and the blue Ultra have the same optical setup and photodetection design. All systems contain fiber optic detection for optimal alignment. And every model has an APD detector. Everything else equal, the main difference between the red and the blue series is the laser. While the red series uses a 10mW HeNe laser, the blue series contains a 4mW HeNe light source for the system. So this means a different factor for the Zetasizer blue sensitivity.

How to use the sensitivity calculator?

The first input box in the sensitivity calculator is for the molecular weight of an example polymer. We used polystyrene in THF as a model system. Simply enter the expected molar mass of your polystyrene molecule in kilo Dalton [kDa]. Once you enter a number in the molecular weight box, the sensitivity values then update on-screen. We selected polystyrene in THF because it is a common standard in chromatography. And it has a known dn/dc refractive index increment or “contrast”.

Why different sensitivity values?

There are basically two versions of sensitivity, one for size and the other for zeta:

• DLS or size sensitivity. This is the minimum concentration for performing dynamic light scattering or size measurements. For instance, there are different values for different single scattering angles. (backscattering at 173°, side scatter at 90°, forward scatter at 13° ). However, yet another value for performing MADLS (for combining back, side, and forward to obtain higher resolution).
• ELS or zeta sensitivity. This is the lowest concentration for performing electrophoretic light scattering or mobility measurements. Zeta measurements are always at a forwarding angle, so provide a single blue sensitivity value.

Hope this calculator leads you to the correct minimum concentration for your blue Zetasizer Blue model! Thanks for using the Zetasizer blue sensitivity and size calculator for polymers.

Previously

• Sensitivity Calculator for the Red Zetasizer Series
• Description of the Zetasizer Advance series, in bullet points
• How to get technical support for your instrument

Have any questions? Please email me ulf.nobbmann@malvern.com – Thanks! Opinions are those of the author. Our editorial team modifies them occasionally.