Hello, welcome to part 2 of our three part video series on Zeta Potential analysis.
Today we’re going to be discussing how to make a measurement and also discussing some
other practical concerns as well.
Our discussion today is going to be centered around a Malvern Zeta Sizer Nano ZS instrument
which is a very popular choice in both industry and academic labs.
Instruments from other manufacturers operate on similar principles and should follow fairly
similar procedures for testing as well.
By far the most important thing to consider in your quest for good zeta data is sample
preparation.
In preparing a sample for zeta potential analysis, you need to consider size, conductivity, ionic
strength, and sample concentration.
According to Malvern, the ZetaSizer Nano can detect particles with diameters between 3.8
nm and 100.0 um for Zeta Potential analysis.
There is a very strong relationship between the diameter of a particle and the intensity
of light scattered from it, so concentration requirements will vary.
This table provided by Malvern shows the recommended sample concentrations of different size ranges.
Note that the table is modeled after polystyrene latex which has a density of around 1 g/cm3,
so your sample needs may vary proportionally.
When a sample has insufficient signal, the resulting measured Zeta Potential value is
low in magnitude.
Low signal is indicated by Mean Count Rates that are below 100 thousand counts per second.
This can happen due to a sample that is too dilute, or a sample that is overly concentrated
due to a phenomenon called multiple scattering.
At high electrolyte concentration, the electrodes inside the zeta cell will begin to corrode.
For this reason the instrument reduces the applied voltage to the cells and only an average
zeta potential is obtained, rather than a full distribution.
Malvern refers to this as monomodal analysis mode and it is applied to all samples with
conductivity values over 5 mS/cm.
Although measuring materials Zeta Potential in high salt media is often necessary as it
pertains to certain applications, it is best minimized for routine analysis if possible.
To monitor cell degradation, be sure to check a reference standard frequently when making
multiple measurements of highly conductive samples.
We will be performing this demo with Malvern’s most commonly used consumable product for
zeta analysis, the folded capillary cell, part number DTS1070.
Firstly, be sure to use some DI water to rinse the cell of any dust, residual sample, or
contaminants from previous uses.
After rinsing, give the cell a light shake and a tap to make sure that the water has been cleared out of
the cell.
For sensitive measurements, it can be a good idea to condition the cell by filling the
cell with a small volume of sample, allowing it to incubate for a couple minutes, and then
disposing it and refilling it with fresh sample for testing.
We find that sample volumes of 700 to 800 microliters to be most convenient for filling
these cells.
If you try to use much more than then what happens is the sample is going to overflow
when you go to fit it with the stopper caps.
When you are ready to fill the cell, make sure to carefully and slowly uptake the sample into
the pipette.
Insert the pipette tip into one of the two open ports of the zeta cell and dispense
the sample slowly and evenly
making sure to keep an eye out for any bubbles or voids it makes
along with way.
To that end, it can be helpful to tilt the cell slightly when adding your liquid.
Visually examine the zeta cell for bubbles and other voids and be sure to
tap and flick the cell as necessary to dislodge them as they will impede the flow of
sample during measurement.
Plug each end of the two ports with plastic plugs.
If using a Malvern disposable capillary cell, note that the cells are not symmetrical and
be sure to place it in the instrument with the Malvern logo facing out.
When inserting the cell into the instrument, be sure to do so slowly and carefully so that you can physically feel
the leads on the cell contacting the electrodes in the instrument.
If a sample measures with extremely low zeta potential, conductivity, and count rate,
this contact is the first thing to check.
Within the instrument’s software suite, navigate to the SOP of interest or manually
configure the measurement as necessary, and press Start to begin your measurement.
Measurements can often take more than a few minutes, so be sure to return and clean the
zeta cell afterward by draining it of sample and then rinsing with deionized water.
While the sample is measuring, pay attention to the signal, or count rate, attenuator setting,
conductivity and quality factor.
We’ll cover this and more in part 3.
Well, that concludes part 2 of our zeta potential video series on how to make a measurement.
For more information about zeta potential theory or data interpretation, be sure to check
out the other two videos of our zeta series.
For information about submitting a sample of your own for zeta potential analysis, please
check out our characterization services landing page.
Thanks for watching and I hope to see you in more characterization videos.