How do make a complex solution

Question

If you want to make a chemical solution with a final volume of 1 ml containing

10 mM Tris-HCL (pH 8)

50 mM NaCl

0.5 mM EDTA

1.0 mM DTT

How do you calculate this?

Thank you!

Lisa

Answer 1

Since all concentrations are given in mM units, recognize that mM is mmoles per liter. This is equivalent to micromoles per ml.

mmol / L x 1000 umol / mmol x 1 L / 1000 ml = umol / ml

So, this tells us that for 1 ml, we need....

10 umol Tris-HCl

50 umol NaCl

0.5 umol EDTA

1.0 umol DTT

Since these are in umoles, it is very unlikely that in practice you'll be able to weigh out these amounts unless you have an incredibly sensitive balance. If this is simply an exercise and not meant to be done in practice, then just multiply the umol figures by the molar mass of each in micro grams (instead of grams), and you'll have your masses (in micro grams) to dissolve in a total volume of 1 ml.

In actual practice, what one typically does is to make each stock solution say 10, 100 or 1000 times more concentrated and then use 1/10, 1/100 or 1/1000 of a ml of each and make up the difference with water to make a total volume of 1 ml. For example, if you made each stock soln 100x more concentrated, you'd then use 10 ul of each and 960 ul of water/buffer to make a final volume of 1.0 ml.

If you need additional help on how to do that, let me know and I'll be glad to assist.