preparing buffer - (Mar/23/2005 )

This is my stock:
1M Tris-HCl
1M CaCl2
1M MgCl2

This is what I want in my 10X reaction buffer:
50mM Tris-HCl pH 2.5
10mM CaCl2
10mM MgCl2

I want the total volume of my buffer to be between 3-5mL so if I mess up when using the buffer, I'd still have some left over.

I found the dilution factors for each, so for example, for the Tris-HCl:
1000mM/50mM = 20.
Then I took the total volume/dilution factor to find out how much Tris-HCl I would need: 5mL/20mL = 1/4 mL Tris-HCl

For CaCl2: 1000/10 = 100 fold dilution factor
5mL / 100mL = 1/20mL CaCl2 (same amount for MgCl2)

Then, I added them up and subtracted by 5mL to find how much water I needed to add:
1/4 + 1/20 + 1/20 = 7/20 reaction solutions
5- 7/20 = 93/20 mL H2O

Would doing it this way get me the 10X buffer I need?

yep you're right

There is a short cut to calculating the amounts required. If you are starting with a 1 M stock and want 50 mM final, you need 50 uL per mL of final volume. For 10 mM, you need 10 uL per mL of final volume. So for 5 mL, you need 5 x 50 uL of 1 M Tris and 5 x 10 uL of 1 M CaC2 (and MgCl2) respectively.