4 replies to this topic

[skr07]

My professor assigned me the task of making 50mM Tris at a pH of 7.45 without using 'base' or 'acid', with the final volume equaling 125 mL, and I cannot perform dilutions to reach this goal. I've been trying to find out a way to adjust the pH without using HCl or NaOH, but everything I find says to do that! Please help!

[bob1]

Use a combination of Tris base and Tris HCl (both powders), you will need to calculate the ratios involved - of search out tables of them.

[phage434]

Make 50 mM solutions of Tris HCl and of Tris Base. Mix them together to achieve the proper pH in sufficient volume to have 125 ml minimum. Throw away the extra after you are done adjusting pH.

[Prep!]

Refer Sambrook (Meniatis)
buffer prep without the need to adjust pH is given in that for whatever volume you need but you have to prepare a stock of the two components first...
It is calculated by the Henderson–Hasselbalch equation which takes into consideration pKa values for the the components and theoritically calculats the needed amount for the desired pH!!!

[Prep!]

phage434, on Oct 29 2009, 08:31 AM, said:

Make 50 mM solutions of Tris HCl and of Tris Base. Mix them together to achieve the proper pH in sufficient volume to have 125 ml minimum. Throw away the extra after you are done adjusting pH.

Alternatively if you dont have a reference, as phage says this is a good approach too!!! i would second him on this (you may have to waset the solutions though if you are not careful enough!!!)