Hello Aroona Razzaq

You will have to make 20mM stock solution instead of 100μM, if you need to adjust the DMSO concentration to 0.1% and below for the following working solutions.

From 20mM stock solution, make 1:100 dilution to give 0.2mM diluted stock.

Then,

From 0.2mM diluted stock make 1:10 dilution to give 20μM working solution. (DMSO concentration 0.1%).

From 0.2mM diluted stock make 1:20 dilution to give 10μM working solution. (DMSO concentration 0.05%).

From 0.2mM diluted stock make 1:40 dilution to give 5μM working solution (DMSO concentration 0.025%).

From 0.2mM diluted stock make 1:200 dilution to give 1μM working solution (DMSO concentration 0.005%).

So, all your working solutions (20μM, 10μM, 5μM and 1μM ) will contain DMSO concentration at 0.1% and below.

But if you use 100 μM as stock solution, then the DMSO concentration in

20 μM working solution will be 20%,

10 μM working solution will be 10%,

5 μM working solution will be 5% and

1 μM working solution will be 1%.

In this case, all your working solutions (20μM, 10μM, 5μM and 1μM ) will contain DMSO concentration at 20% and below (till 1% for the final dilution).

So, you may prepare a 20mM stock solution instead of 100μM.

Best.