How do you create serial dilutions of a pure compound while maintaining a 0.1% DMSO concentration in each solution?

Question

I need to test various concentrations of a compound however it is only soluble in DMSO. My compound is in pure powder form (I only have 900mg available, and it will be dissolved in 100% DMSO first). It will be diluted again with culture medium upon exposure to cells. How am I going to create these concentrations: 0.96%, 0.48%, 0.12%, 0.06% (2-fold dilutions) in each series but still maintaining a 0.1% DMSO concentration?

Answer 1

What is the final volume of solution that the cells will be exposed to?  This will ultimately determine how the dilutions are to be done.  Thus, for example, since you will be adding 100% DMSO, and you want the final concentration of DMSO to be 0.1%, this means you need a 1:1000 dilution of the DMSO solution.  If your final incubation volume is, say, 1 ml (containing the cells), then you will have to add 1 ul of the drug/compound solution. This will give you a 0.1% final DMSO concentration.  If you are not planning to dilute the DMSO prior to adding it to the cells in culture, you will run into a problem. That problem is that diluting the DMSO 1:1000 means that you will also have to dilute your compound 1:1000, and this won't be possible based on the amount you have, and presumably, on the solubility.  Why do I say this? To get a FINAL concentration of 0.96%, e.g. after diluting 1:1000 would mean an initial concentration of 9.6 g/ml DMSO. This is unreasonable.

 

So, the final incubation volume becomes critically important.  If it is 1 ml as assume in the above discussion, you will not be able to prepare such solutions without first diluting the DMSO stock solutions.  I hesitate to suggest possibilities without first knowing the final incubation volume, and also knowing what is the smallest volume you are able to measure.  Can you, e.g. measure 1 ul reliably?