Question

Given 200ul of a 0.5mg/ml stock solution of BSA, how much do you pipet into a test tube so that you are adding 10ug of BSA to the test tube? 4ug?  

Answer 1

200 μl of stock solution = 200 microlitre of stock solution = (200 x 0.001 ) ml = 0.2 ml of stock solution

And, 10 μg of BSA = 10 microgramme of BSA = (10 x 0.001 ) mg = 0.01 mg of BSA

Now, 0.5 mg of BSA is present in 1 ml of stock solution

So, 0.01 mg of BSA is present in (1 x 0.01)/0.5 ml = 0.02 ml of stock solution

   =  20 μl  of stock solution

Again, 4 μg of BSA = 0.004 mg of BSA is present in (1 x 0.004)/0.5 ml = 0.008 ml of stock solution

   = 8 μl  of stock solution

Answer 1:  0.02 ml or 20 μl  of stock solution has to be pipeted into a test tube so that you are adding 10 ug of BSA to the test tube.

Answer 2:  0.008 ml or 8 μl  of stock solution has to be pipeted into a test tube so that you are adding 4 ug of BSA to the test tube.

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