You can possibly consider a citric acid / sodium citrate buffer to attain a pH 3.0 aqueous solution; the following internet site may assist you preparing this solution:

http://www.sigmaaldrich.com/life-science/core-bioreagents/biological-buffers/learning-center/buffer-reference-center.html#citric2

Hi Carlos,

Thanks a lot. 

Hi, I need another pH 9 buffer. Carlos? 

Dear Monokesh Sen:

While suggesting a protocol for dissolving azocasein, I have included that of preparing a Na2CO3 / NaHCO3 aqueous buffer solution of pH ≈ 9.2 (20 ºC): https://www.researchgate.net/post/how_does_azocasein_dissolve_in_water

Thanks a lot Carlos. 

Hi, how can I get pH 14 buffer. Carlos? 

thank you