I checked all the page on internet and in research gate. But my doubt is about the molarity. I was thinking in make up the two dillutions of 10nM of sodium acetate and 10nM of acetic acid and mix them to have the same molarity. But I dont know how many of each one I should use. (I supose that use it until get pH4 but I think it will change the molarity because is more water so my idea was make a solution concentrated of sodium acetate and acetic acid and when the pH be 4 add more water), but I am not sure if that will change he molarity of the acid later or not. I think that not... but I want to be sure, because each place I visited internet say something different and that was my idea since the begining but I prefer an answer of an expert mind that mine
I would suggest you prepare it in that way ,it won't affect the molarity of the solution.
You can also prepare by Using sodium acetate trihydrate (MW=136.09g/mol)
-Dissolve 13.61g of sodium acetate trihydrate in 800ml of DI water and mix using a magnetic stirrer with the pH meter to check the pH.
-Adjust the pH by adding glacial acetic acid to adjust pH until pH 4.
-Then transfer into 1L volumetric flask and adjust 1000ml with DI water.
or you can prepare 1M of sodium acetate and 1M of acetic acid then adjust the pH until pH 4.Then from that you can prepare 10mM of acetate buffer(10ml of 1M sodium acetate buffer pH 4+ 990ml of DI water to make up 1L).Check pH of your final solution after preparation .
NB-Buffer consists of a conjugate acid and conjugate base.