calculate the molarity of the TEA using the information on the bottle

Molarity = percent concentration (g/g) X density (g/ml) X 1000 (ml/L) divided by the molar mass (moles/g).

take appropriate amount of TEA and adjust the pH using acetic acid. Since you would be adding methanol, you have to the pH may change.

Reposting again:

take appropriate amount of TEA and adjust the pH using acetic acid. Since you would be adding methanol to this buffer, add appropriate amount of methanol and then adjust the pH

So you mean I prepare the buffer separately then add the mobile phase later? I have never prepared a buffer before, sorry for the bothering. So when you adjust the pH, I will be stirring and a pH measuring device in the mixture?

Hello,

I Just want to add some information on your question.As Sharad sir has already added answer. But, generally it is not advisable to adjust the pH of final mobile phase with organic component in it. Because if organic proportion in your mobile phase is very high pH meter will show fluctuations in pH values and it will not be stable.

The general practice is to adjust the pH of your aqueous buffer phase as per method or procedure. In your case i think it will be acetic acid and if pH becomes acidic and you need to adjust pH to basic side in that case adjust the pH using dilute solution of TEA.

After preparation of buffer add organic component, in your case it is methanol. Mix both the phases by stirring ensure proper mixing of both the phases, degas it and then use it.

Thanks.