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# Dilution question

3 replies to this topic

### #1 biobegin

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Posted 13 March 2013 - 11:42 AM

Hi Everyone,

I am new to this forum and to the world of Bio!
Can anyone help me with this dilution-I am asked to do a 2-fold serial dilution of mixing a bacteria (from a bacterial stock) and to a final volume of 75 ul. How is this dilution different than 10-fold dilution? What formula can I use to solve this dilution problem? Please helppppppppp me!

Thanks

### #2 pcrman

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Posted 14 March 2013 - 10:34 AM

2-fold dilution is a bit confusing, a better way of describing dilution is ratio. for example, 2 fold dilution equals to 1:2 dilution. since you mentioned serial dilution, you do this by first mixing an equal volume of bacteria and water (whatever used for dilution), and then mix an equal volume of the first mixture and water.

for 10 fold serial dilution, you do the above 10 times. If you don't mind the intermediate steps (for example you don't need serial concentrations), you can jump to the final dilution by omitting the middle ones, and do this by calculation.

For example, if you want to have 75 ul 10-fold diluted bacteria, the volume of original bacteria needed is x,

x = 75 ul /10 fold = 7.5 ul

you take 7.5 ul bacteria and add 62.5 ul water to make 75 ul final solution.

### #3 leelee

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Posted 14 March 2013 - 06:19 PM

Actually, if you are talking about a ratio, then a two fold dilution is 1:1
That is, one part bacteria to 1 part diluent.
1:2 means 1 part bacteria to 2 parts diluent (or a 3 fold dilution).

Often scientists use this ratio notation incorrectly, so quite often, people will still know what you mean, but I can't help myself from pointing out it is wrong..... I can be a know-it-all sometimes

Edited by leelee, 14 March 2013 - 06:20 PM.

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### #4 mdfenko

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Posted 15 March 2013 - 05:14 AM

and 62.5+7.5=70 (i really am a nitpicker)

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