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# need dilution help

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### #1 claritylight

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Posted 06 December 2010 - 03:36 PM

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?

### #2 sara27

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Posted 06 December 2010 - 05:31 PM

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.

### #3 claritylight

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Posted 06 December 2010 - 08:53 PM

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.

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?

Edited by claritylight, 06 December 2010 - 08:54 PM.

### #4 sara27

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Posted 06 December 2010 - 09:33 PM

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.

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?

yep the math looks right to me.

### #5 claritylight

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Posted 07 December 2010 - 03:59 AM

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?

### #6 sara27

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Posted 07 December 2010 - 10:26 AM

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?

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)

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