Hello, we are studying on electrophoretic ceramic coating. We performed zeta potential analyzes using zetasizer to decide whether the ceramic slurry prepared is suitable for the EPD method. We encountered the error of “RESULT DOES NOT MEET QUALITY CRITERIA- Sample concentration may be inappropriate (too high or low)” in zeta measurements made with a suspension containing 50% w/v water. We used disposable capillary cell (DTS1070) during measurement. What should be the concentration of ceramic slurry for zeta potential measurement? Which cell is suitable for measurement?
Esma Akci
Most importantly, the suspension should be stable during measurement. For electrophoresis technology it should be as concentrated as possible. Therefore, select a concentrated stable suspension and measure the zeta potential.
Thank you for your answer. I performed measurements by preparing suspensions with different concentrations until the analysis results met the quality criteria. The zeta potential measurement of the suspension with very high water content (100ml water + 0,5g RTU) met the quality criteria (as shown in figure). However, I am not sure of the accuracy of the results as the concentration difference between the sample suspension and the EPD suspension is very high.
Hello Esma Akci the concentration depends on the sample properties. In your case, the sample was probably too turbid, so there was not enough light making it through the cell to be able to get good statistics. There are two possible ways around that:
- dilute the same
- use a smaller path length cell
You managed to get good data with the lower concentration. Here you have to keep in mind how to dilute to avoid influencing your sample. In principle, only the supernatant of the spun down sample should be used to make sure, the diluent remains the same. There is an application note you might find interesting https://www.malvernpanalytical.com/en/learn/knowledge-center/application-notes/AN101104HighlyConcentratedCMPSlurry.html and you may also find this blog on zeta deviation relevant Version:https://www.materials-talks.com/blog/2017/09/05/what-is-the-zeta-deviation/
Esma Akci
No system measures zeta potential (ZP) directly - mobility in an electrical or acoustic field is measured and then converted by appropriate algorithm to zeta potential.
At high concentrations then you can get hindered mobility (the apparent slower movement increasing the apparent particle size or decreases the magnitude of the ZP) obtained in conversion or multiple scattering (thus reducing the apparent size). A mobility can always be made, but the conversion to ZP or size may be problematical. Thus measurements are normally made in fairly dilute (with the mother liquor) suspensions although a concentration ladder is recommended by the international standards (ISO22412:2020; ASTM E2490-09(15)). If you dilute correctly in the mother liquor (never in DI water) then the particles are in the same ionic medium that it started with and just more separate.
As Ulf states, you need to get light in and out of the system to effect a measurement. This may be more difficult in a 90 degree system in a square cuvette rather than in a back-scatter mode. Which instrument do you have?
Thank you for your answer. I have Zetasizer Nano ZS and I use disposable capillary cell (DTS1070) for the zeta potential measurement. The zeta potential measurement of the suspension with very high water content (100ml water + 0,5g RTU) met the quality criteria. However, is not the difference between the sample suspension and the EPD suspension very high? Can I obtain more accurate results by using high concentration zeta potential cell zen1010? Alan F Rawle
Esma Akci
You are not measuring zeta potential - the instrument is measuring mobility. Accuracy is always defined against a known certified reference material. I assume you’ve run the transfer standard? A dilution ladder is obligatory. Dilution must be with the mother liquor and not with DI water. Concentrated systems may have hindered movement.
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