# Serial Dilutions HelpWatch

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#1
I have been provided with a sample containing 20ug/ul of DNA. The values for Tube 1 have been provided: CONC. OF DNA = 20ug/ul, VOL. OF WATER ADDED = 0ul, FINAL VOLUME OF DNA = 100ul, FINAL VOLUME IN TUBE = 100ul. Tube 2 is a dilution of Tube 1. The values for Tube 2 that have been given are: CONC. OF DNA = 2ug/ul, FINAL VOLUME IN TUBE = 100ul. I need to find the volume of water added and the final volume of DNA but I don't know how. Can anyone help?
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1 year ago
#2
10 microlitres of DNA and 90 microlitres of water
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#3
(Original post by BobbJo)
10 microlitres of DNA and 90 microlitres of water
How did you work this out?
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1 year ago
#4
(Original post by SultanOE)
How did you work this out?
For 20 ug/ul -> 2 ug/ul, the concentration goes down by 1/10. Hence you need 1/10 as much DNA

so only 10 uL of DNA is needed. you add 90 uL on water to make volume to 100 uL. this 100uL contains only 1/10 the DNA in the original tube. so the concentration is 1/10 the original which is 2 ug/ul which is exactly what we want
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#5
(Original post by BobbJo)
For 20 ug/ul -> 2 ug/ul, the concentration goes down by 1/10. Hence you need 1/10 as much DNA

so only 10 uL of DNA is needed. you add 90 uL on water to make volume to 100 uL. this 100uL contains only 1/10 the DNA in the original tube. so the concentration is 1/10 the original which is 2 ug/ul which is exactly what we want
and what if for tube 3, the DNA conc is 1ug/ul?
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