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  #1  
Old 10-24-2009, 12:22 PM
mara
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Default mg/ml to volume fraction

Hi,

Can someone tell me as to how I can convert mg/ml of protein solution to volume fraction?

Thanks
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  #2  
Old 10-24-2009, 09:34 PM
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Default Re: mg/ml to volume fraction

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Originally Posted by mara View Post
Hi,

Can someone tell me as to how I can convert mg/ml of protein solution to volume fraction?

Thanks
Volume fraction is finding out how much space one compound takes up in the final dispersion or solution, and is often given as %v/v.

It is quite hard to see why you would need to do this for a protein, so i might be misunderstanding what you are asking? If you have some sort of density value for your protein, then work out the volume of protein divided by the total volume.

Please post back if this is not what you need to know.
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  #3  
Old 10-25-2009, 04:38 AM
mara
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Default Re: mg/ml to volume fraction

I don't have the density value of my protein. But, say I have prepared 10mg/ml protein and use only 50 ul of that solution, how can I find the volume fraction? I came across a paper (Langmuir 2007, 23, 5498-5505) where they convert the concentration of a protein to its volume fraction. I am not sure how they did it. Would finding the volume of one protein molecule and solving from there be a possible or valid way?

Thanks.
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  #4  
Old 10-25-2009, 05:02 AM
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Default Re: mg/ml to volume fraction

Quote:
Originally Posted by mara View Post
I don't have the density value of my protein. But, say I have prepared 10mg/ml protein and use only 50 ul of that solution, how can I find the volume fraction? I came across a paper (Langmuir 2007, 23, 5498-5505) where they convert the concentration of a protein to its volume fraction. I am not sure how they did it. Would finding the volume of one protein molecule and solving from there be a possible or valid way?

Thanks.
If you use 50 L of a solution with concentration 10 mg /mL, you only need to know that 1 mL = 1000 L
Thus 10 mg/1000 L * 50 L = 0.5 mg of the solute.
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  #5  
Old 10-25-2009, 10:53 AM
Mara
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Default Re: mg/ml to volume fraction

Yes, true, that gives the mass (weight), but how can I get the volume fraction?

Thanks
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  #6  
Old 10-25-2009, 11:09 AM
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Default Re: mg/ml to volume fraction

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Originally Posted by Mara View Post
Yes, true, that gives the mass (weight), but how can I get the volume fraction?

Thanks
You'd have to have a density figure for pure protein, out of solution. I'm not sure that makes sense.
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  #7  
Old 10-25-2009, 05:29 PM
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Default Re: mg/ml to volume fraction

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Originally Posted by mara View Post
Would finding the volume of one protein molecule and solving from there be a possible or valid way?

Thanks.
There may be a problem looking at it this way, PARTICULARLY with proteins. The volume of a single molecule might not be the same as several molecules added together. They may not fit together perfectly, OR they might fit more closely togther than what the volume of one molecule would suggest they do.

Is there any other way you can approach the problem? For example, can you add a known volume of water to a known weight of protein, and measure the volume of the resulting mix?
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  #8  
Old 11-07-2013, 10:41 AM
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Default Re: mg/ml to volume fraction

Typical protein density might be taken as 1.451 g/cm^3 at 20oC

if in doubt, you can measure the density of your protein solution to back calculate the protein density... Solution density = water% x 0.998 + protein % x protein density...
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