# basic dilution question - (Feb/19/2009 )

I have a question on how to calculate my original stock concentration from a diluted sample.

My DNA sample concentration is very high and my spectrometer has some limit to it. So I diluted my sample 1/20 in TE, measured the concentration again, and it was 120 ng/mL.

How do I calculate my original concentration from this information? There must be a formula but I don't remember.

claritylight on Feb 19 2009, 12:29 PM said:

My DNA sample concentration is very high and my spectrometer has some limit to it. So I diluted my sample 1/20 in TE, measured the concentration again, and it was 120 ng/mL.

How do I calculate my original concentration from this information? There must be a formula but I don't remember.

I think u stock concentration might be 2.4ug/ml... Well this is how i calculated, if 1/20 gives 120ng/ml, then 1 should give, (1 x 120) / (1/20) which is 120x20 = 2400ng/ml, which is 2.4ug/ml.. I hope I am right... Please recheck with others as well...

Good luck...

Yea the 2.4 ug/ml is right. When you dilute your sample 1/20, that means your stock is 20 times as concentrated as your dilution. So multiply the concentration of the diluted sample by 20 to get the concentration of the stock. 120ng/ml x 20 = 2400ng/ml = 2.4 ug/ml

thanks!

unless you made the dilution by adding 1 to 20, then you would multiply by 21 if you want to be exact.

so it could be

1 ul sample

and 19 ul solvent