# Preparing an extraction buffer with PMSF and 2-mercaptoethanol

1. Jan 16, 2012

### samzorz

1. The problem statement, all variables and given/known data

We have a 100 mL of 10 mM Tris-HCl, 1 mM EDTA, pH = 7.4

We're supposed to add PMSF to a final concentration of 1 mM and 2-mercaptoethanol to a final concentration of 1 mM. The stock solution of PMSF is .10 M PMSF in absolute ethanol. The 2-mercaptoethanol is also in the hood, it is 14.3 M.

We're trying to find the volume of .10 M PMSF needed and the volume of 2-mercaptoethanol needed

2. Relevant equations

M1V1=M2V2?

3. The attempt at a solution

Not sure how we can use the equation if we have 2 concentrations

2. Jan 17, 2012

### Staff: Mentor

Two ways of approaching the problem.

1. Calculate both volumes to be added assuming volume of the "main" solution doesn't change. Especially if you start with 2-mercaptoethanol that will be very close to correct.

2. Add first solution (say - PMSF) and calculate how much 2-mercaptoethanol to add assuming your volume is now sum of volumes of the "main" solution and PMSF solution.

3. Jan 19, 2012

### epenguin

You will do a 100X dilution of the PMSF, so the change of volume due that too is insignificant.

You may need to or find it practically convenient to dilute the mercaptoethanol in two stages.

More refined calculations are IMO pointless here - I suspect for what you are going to do even a 100% error would probably make no difference and you will have a teacher/lab supervisor chomping for you to get on with it!

Last edited: Jan 19, 2012
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