did you try looking for surfactants used in the synthesis of calcium phosphate? There are several articles and, if you cant' access any other bibliographic source, a google search for sure can give you some feedback.

What I do not understand is the fact you want to measure the zeta potential while keeping the particles separated. The zeta potential is clearly low if the particles agglomerate...

Dear Matteo Leoni, Thanks for help. I want to measure calcium phosphate nanoparticle(CANP) size and zeta potential both. But when Im dispersing the CANP in the distillled water, they agglomerate immediately in the cuvette itself and Im getting wrong particle size or zeta potential. Please let me know if you have any publications or links related to this matter....

@Matteo Leoni & Jyoti Saikia, Sir Thank you very much for help. If you have any idea/Literature about suitable surfactant or dispersing medium for Calcium Phosphate Nanoparticle. Please let me know.

don't go for size analysis with zeta analyzer since its gives bigger size than the actual size, as it calculate the hydrodynamic size of the particle. use TEM for size measurement.

Agree with Mr Arun Karthick

For size measurement, TEM is most preferred. You can use FESEM analysis also using dry powder nano-particle for size measurement. PSA or Zeta potential analysis will give readings of agglomerate size, which will be in micron sizes. Further more, to improve stability of your nanofluid, Mechanical mixing (ultrasonication) or surfactant can be used to reduce agglomeration but still there will be small agglomerated present which will effect your reading.

Thank you very much dear Arun Karthick and Suhaib Ilyas for help and valuable suggestions.......

How did you solve this problem? I also have this problem