You have three BSA working solutions: 5ug/ul, 0.5 ug/ul, and 0.05 ug/ul. Each tube contains 500 ul of solution. How much of which concentration(s) would you pipet into three different centrifuge tubes so you end up with 20 ug, 2 ug, and 0.2 ug of BSA in each tube

I would pipet 4 μl of each BSA work solution

Explanation:

To calculate the mass (in μg), we have to multiply the concentration C (in μg/ul) by the volume V (in μl):

C(μg/ul) x V( μl) = mass (μg)

We found the required volume for each solution, as follows:

5 μg/μl x V₁ = 20 μg ⇒ V₁ = 20 μg/(5 μg/μl ) = 4 μl

0.5 μg/μl x V₂ = 2 μg ⇒ V₂ = 2 μg/(0.5 μg/μl) = 4 μl

0.05 μg/μl x V₃ = 0.2 μg ⇒ V₃= 0.2 μg/(0.05 μg/μl) = 4 μl

Therefore, we need to pipet 4 μl of the solutions of concentrations 5μg/μl, 0.5 μg/μl, and 0.05 μg/μl to obtain the masses 20 μg, 2 μg, and 0.2 μg, respectively.