I am working on a toxicity test and I want to set the pH of EPA medium to 5, 6, 7, 8, 9.

I am planning to use zwitterionic buffers in powder form (MES, MOPS, etc.) to set these specific pH's as they have less biological interference and metal complexity.

But I am unable to understand how. I know the pKa values of these buffer compunds, how can I make an EPA-buffer system of the desired specific pH values.

Please let me know if anyone has used such buffer systems before, would really appreciate the help.