I am using a cationic amphiphile (similar to benzalkonium chloride) having iodide as counter ion and formulated nanoparticles in 7.4 PBS. Nanoparticles formed are having sizes around 100nm and good PDI. However I am facing problem with measuring zeta potential. When the measurment is going on zeta cell is releasing a dark brown precipitate into the nanoparticle solution and readings are not constant. However when the formulation was made in water, no such pecipitation was observed. Can anyone please explain me why the zeta cell is reacting when formulation is made in 7.4 PBS to give a brown precipitate?
Attached are the photos of the nanoparticle solution having brown precipitate after measuring zeta potential.
You have electrochemical reduction of your organic material. What instrument are you using? Reducing the voltage significantly can help but the barrier method keeps organic material away from the electrodes. See: https://www.malvern.com/en/support/events-and-training/webinars/W110614ProteinZetaPotentialDiffusionBarrierMethod.html
Thank you very much for the suggestion Mr. Alan F Rawle. I am using Malvern Nano ZS.
Then take a look on the Malvern.com website searching out the webinars on diffusion barrier method. There's also a patent which I attach.
Just thought to check if you were able to solve the issue. Did the diffusion barrier method keep your sample monodisperse? Reducing the applied voltage can also help to limit the exposure of delicate samples during the measurement. It is always a good idea to measure DLS size before and after zeta, to check that the sample remains the same after being subjected to the electric field.
http://www.materials-talks.com/blog/2015/11/24/diffusion-barrier-method-the-practical-details/
Hi Pavan.
According to my experience, it could be the following reasons: (1) high salt concentration (> 5mS/cm); (2) electrodes already dirty before measurement. Choosing the desired pH and ion strength are important in zeta potential measurements.
Good luck,
Dongyu
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