Question

I have a tricky dilution question. You have a stock solution of methylene blue at 1g/100ml. Make 250ul of methylene blue at a concentration of 150ug/100ml with as little waste as possible (have as little excess as possible). So I have the dilution formula C₁V_{1 =} C₂V₂. That means (1g/100ml)V₁ = (150ug/100ml)(250ul). I converted C₁ to ug and got 10⁶ug/100ml which reduces down to 10⁴ug/1ml. Please correct anything I may have wrong. Next I cnverted V₂ to ml to keep units the same and got 0.25ml. From here I multiplied 1.5ug(0.25ml) and got 0.375ug/ml. Next I divided the left and right side by 10⁴ug/ml and got 3.75 x 10^-5ug/ml. I'm stuck trying to figure out how to do it from here because that volume is much to small to be measured by a pipette. I'm thinking I'd have to dilute the stock solution or a portion of it, but again am stuck. Thanks for your help

Answer 1

The initial concetration is 1g/100ml. So you have to prepare 250ul (0.25ml) at a concentration of 150ug/100ml. (0,15mg/100ml).

Now, if we take 0.15ml of initial solution and we add water unitl to make 1L (or you can take 1,5ml and add water until to make 10L), you get:

If you take 0.25ml, 100ml or 1ml of this final solution the concentration will be 0.0015mg/ml.