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#1
10-24-2009, 12:22 PM
 mara Guest Posts: n/a
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
#2
10-24-2009, 09:34 PM
 Mrs X can't count, can't spell! Join Date: Feb 2006 Location: New Zealand Posts: 2,412 Rep Power: 12
Re: mg/ml to volume fraction

Quote:
 Originally Posted by mara 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.
#3
10-25-2009, 04:38 AM
 mara Guest Posts: n/a
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.
#4
10-25-2009, 05:02 AM
 JohnS Moderator Join Date: Dec 2007 Location: SE Michigan, USA Posts: 9,439 Rep Power: 19
Re: mg/ml to volume fraction

Quote:
 Originally Posted by mara 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 µL of a solution with concentration 10 mg /mL, you only need to know that 1 mL = 1000 µL
Thus 10 mg/1000 µL * 50 µL = 0.5 mg of the solute.
#5
10-25-2009, 10:53 AM
 Mara Guest Posts: n/a
Re: mg/ml to volume fraction

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

Thanks
#6
10-25-2009, 11:09 AM
 JohnS Moderator Join Date: Dec 2007 Location: SE Michigan, USA Posts: 9,439 Rep Power: 19
Re: mg/ml to volume fraction

Quote:
 Originally Posted by Mara 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.
#7
10-25-2009, 05:29 PM
 Mrs X can't count, can't spell! Join Date: Feb 2006 Location: New Zealand Posts: 2,412 Rep Power: 12
Re: mg/ml to volume fraction

Quote:
 Originally Posted by mara 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?
#8
11-07-2013, 10:41 AM
 Unregistered Guest Posts: n/a
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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