MadSci Network: Biochemistry |
Blimey, Shaun, that's a really technical question! You have two options, one based on theory and one based on making measurements. I'm going to recommend the latter. In theory, you could find the pKa of each vitamin. The pKa is the pH at which a compound is half-acidified. Now, pKa's are often available in texts but you would have to establish values for each vitamin and correct the values for temperature and salt concentration. Done that? No, I wouldn't have thought so; especially as you now have to calculate how much buffer to add by finding the pKa's of the buffer components and using an equation first derived by Henderson and Hasselbach (quite a well-known one that I won't quote here). I hope that I have put you off the theoretical method! I would get myself a pH meter, measure the pH of a vitamin sample, and add buffer until the required pH was obtained. You might need to do this for each new vitamin mixture but soon you should have a good book of recipes for making the solutions correctly. If you are lucky, the manufacturers of the vitamin and buffer vials should be able to give you recipes - after all, their products are designed for this sort of use, so why not ask them how to do it? I hope that this is helpful - I know it's not the answer you were after but I spent many years making up solutions to a given pH and found that the only reliable method is to use a pH meter. Calculations are always going to give approximate results anyway. Do get back to me if there are any other points you need answering! Ewen McLaughlin
Try the links in the MadSci Library for more information on Biochemistry.