Hello everybody,

I need to prepare such a buffer buffer. Its composition is:

20 mM citrate/ 20 mM phosphate/20 mM Tris pH 3.5 and the same with pH 7.

Should I prepare this my doing the following steps:

1. Add 20 mmol/L of Sodium citrate dihydrate 

2. Add 20 mmol/L of sodium phosphate dibasic (heptahydrate) 

3. Add 20mmol/L of Trizma base

4. And then adjust pH to 3.5 and pH 7 for the second buffer with HCL and NaOH respectively and add water to 1L?

Or maybe I oversimplified and to make 20mM phosphate I have to mix sodium phosphate monobasic and dibasic in the correct ratio the same way as when making phosphate buffer, then prepare citrate buffer by mixing sodium citrate dihydrate with citric acid and then prepare Tris, and mix them but then which base or acid to use to adjust pH?

Any ideas will be appreaciated. 

Regards