need dilution help - urgent (Dec/06/2010 )

If I have a sample that reads 280ng/ul and I only have 3ul left of the stock DNA, how do I make 10ng/ul dilution with final volume of 200ul from the stock?

Its not possible to get a 200ul dilution at 10ng/ul from 3 ul of your stock DNA. 200ul at 10ng/ul means you have a total of 2000ng, while you only have 3ul at 280ng/ul, or 840 ng total DNA to start with. if you dilute your sample to a total of 84ul (add 81ul) then you will have 10ng/ul, but only 84 ul of it.

sara27 on Tue Dec 7 01:31:16 2010 said:

Thanks. I would like a bit more volume than 84ul. I can also bring the final concentration down to between 4-5ng/ul. I have tried this math:

Ideally, I would like the following:
using C1V1 = C2V2 formula
C1 = 280ng/ul
C2=10ng/ul
V1 = x
V2 = 200ul
V1 = 10*200/280
V1 = 7.14ul stock DNA + 192.8ul water
Where (7.14ul/200ul)*280 = ~10ng/ul

Since I don't have 7.14ul stock DNA, I entered in what I have left:
(3ul/200)*280 = ~4.2ng/ul...this will be ok, I will have 4.2ng/ul at 200ul final.

But does this math look right to you? Does it make sense?

claritylight on Tue Dec 7 04:53:34 2010 said:

yep the math looks right to me.

thanks for checking. one last question, how do I use your method to make up the amount that I did? I know what you had done (3ul/84ul)*280ng/ul = 10ng/ul, but couldn't figure out how you got 81 in the first place. What formula did you use?

claritylight on Tue Dec 7 11:59:42 2010 said:

there was no formula. the equation will give you the total volume (84ul). since you already have your DNA in a total of 3ul volume, you need to add 81ul to make the 84ul final volume. (84ul-3ul=81ul)