Dear Chidi, Can you clarify your question as 10ug in 30uL=333ug/mL which is more concentrated than your stock solution of 20ug/mL? Do you want to get 30uL of a 10ug/mL solution? In any case what is the purpose of it? Quantitative analysis? Semi-quantitative? What analytical glassware/hardware (e.g. micropipette) is available?

Yea from my stock of 20ug/ml i need 7 concentrations diluted in halfs 10...5...2.5....1.25....... I am using it for drug test in a 96well plate and I need these concentration in small volume  (30ul)...I have micropippette

An acceptable approach would be to pipette to the 1st well (or to each of the 1st row of wells) 30uL of the stock solution and then pipette 30 uL of the solvent. Homogenize the mixture by aspiring/dispensing several times. Now you have 60uL of a 10ug/mL solution in the 1st one.

To the 2nd well (or 2nd row of wells) pipette 30 uL from the 1st well and then pipette 30 uL of the solvent. Homogenize the mixture by aspiring/dispensing several times. Now you have 60uL of a 5ug/mL solution in the 2nd one.

To the 3rd well (or 3rd row of wells) pipette 30 uL from the 2nd well and then pipette 30 uL of the solvent. Homogenize the mixture by aspiring/dispensing several times. Now you have 60uL of a 2.5ug/mL solution in the 3rd one.

...

...

To the 7th well (or 7th row of wells) pipette 30 uL from the 6th well and then pipette 30 uL of the solvent. Homogenize the mixture by aspiring/dispensing several times. Now you have 60uL of a 0.15625 ug/mL solution in the 7th one.

Finally remove 30uL from the 7th well and discard them.

You end up with 30uL in each of the 7 wells with the following concentrations: 10, 5, 2.5, 1.25, 0.625, 0.3125, 0.1565 ug/mL.

You should be aware that this procedure is very practical from the experimental standpoint but suffers from the fact that the concentrations are not independent (the 7th solution is obtained by diluting the 6th one which in turn is obtained by diluting the 5th one which...) which requires proper statistical analysis. Any error in obtaining any intermediate solution will propagate to the subsequent ones. Proper care (read extra care) should be taken.

Hope it helps (if so, please upvote)

Thanks Luis this really helps can simply make these concentrations as directed in an ependorff tube ? Cos I have to seed the plates with test cells before adding the concentrations

Yes Chidi. In that case I would suggest to start with 45uL stock + 45 uL solvent, and then take 45uL to the 2nd, add 45uL solvent,.... instead of 30 + 30....

This way you can always be able to draw 30uL from the eppendorf to the well.

Many thanks Luis well appreciated