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ScottyMcGeester's avatar

Dilution factor problem?

Asked by ScottyMcGeester (1002 points ) September 28th, 2012

So I did these dilutions – 1:2, 1:4 and 1:10

I’m doing these in microliters. So for example, the 1:2 dilution was 500 microliters of this protein I’m using and 500 microliters of buffer. (Or also .5ml and .5ml, get it? Because each dilution is supposed to be 1ml total)

1:4 was 750 microliters and 250 microliters, then 1:10 was 900 microliters with 100 microliters.

So that went well and all. But now I need to do dilutions of 4:10, 325:100, and 175:100

And to this I say “What the hell?”

How many microliters then is that for the protein vs buffer for each?

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4 Answers

dxs's avatar

Just make a proportion. Four tenths is what fraction of a milliliter? Four tenths equals how many microliters over one thousand microliters?
(Ignore the dots please)
4 ....... x μL
— =....—
10….1000μL
Cross Multiply so that 4000μL=10xμL. Now just make it so that x is on one side of the equation and you’ll get the amount of the protein in the dilution.

LostInParadise's avatar

I think you are misinterpreting what is meant by dilution factor. By your reasoning, a dilution factor of 325:100 would give a resulting concentration of over 3 times the original. That can’t be right. It should be that, for example,1:2 means 1 volume of protein to 2 volumes of buffer. That would give ⅓ ml of protein and ⅔ ml of buffer. The other protein concentrations would be 4/14 ml, 325/425 ml and 175/275 ml.

ScottyMcGeester's avatar

@LostInParadise Well, technically this a serial dilution. I should have made that clear in the question. I see your problem as I’m trying to do what @dxs told me. Although, what you’re saying about 1:2 confused me – my boss directly told me what to do, and he told me that it was .5ml of protein and .5ml of buffer for the 1:2 dilution. He gave me a hint as to the 4:10, something about it being 80% of the 1:2 dilution . . .

Unless. . . . oh crap, I’m sorry. 1:2 is a ratio. I mean ½ dilution. So meaning half a dilution of the original stock solution.

ScottyMcGeester's avatar

This doesn’t make sense then. Each dilution tells me really how many milliliters I need. For example, ½ = .5 So it’s going to be .5ml and .5ml. ¼ is .25, so the other half will be .75. 1/10 is .1, so the rest will be .9. 325/100 would give me more than 1ml. Since it would be 3.25. As would 175.

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