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# basic dilution question

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### #1 claritylight

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Posted 19 February 2009 - 12:29 PM

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.

### #2 molecular_medicine

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Posted 19 February 2009 - 12:53 PM

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.

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...

### #3 sara27

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Posted 19 February 2009 - 03:43 PM

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

### #4 claritylight

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Posted 20 February 2009 - 06:40 AM

thanks!

### #5 mdfenko

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Posted 20 February 2009 - 07:03 AM

unless you made the dilution by adding 1 to 20, then you would multiply by 21 if you want to be exact.
talent does what it can
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### #6 Felipillo

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Posted 23 February 2009 - 08:19 PM

so it could be

1 ul sample
and 19 ul solvent
Chance favors the prepared mind
Louis Pasteur.