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### How to convert % to ug/ml or ppm or vice versa?

Posted: Mon Apr 27, 2020 5:14 am
If a solution contains 70% Ethanol, how much would this equate to in ug/ml or ppm.

Or if a solution contains 5000 ug/ml of ethanol, how much would that be in %?

### Re: How to convert % to ug/ml or ppm or vice versa?

Posted: Mon Apr 27, 2020 2:12 pm
It's a trick question. You need to specify if the % is w/v or w/w or v/v

That's why concentration should never be given in % or ppm.

### Re: How to convert % to ug/ml or ppm or vice versa?

Posted: Mon Apr 27, 2020 3:03 pm
tom jupille wrote:
It's a trick question. You need to specify if the % is w/v or w/w or v/v

That's why concentration should never be given in % or ppm.

V/V

### Re: How to convert % to ug/ml or ppm or vice versa?

Posted: Tue Apr 28, 2020 7:59 pm
Your second question is easier -- but the answer may not be meaningful.
5000 ug/mL = 5 mg/mL = 0.005g/mL
To get V/V, you need to convert that 0.005 g to mL, so you divide by the density of ethanol (0.8 g/mL) which gives you 0.006 = 0.6% . At that low a level, any volume contraction on mixing will be negligible (see next paragraph).

The first question is more complex because of the volume contraction when you mix ethanol and water. If you ignore that, the calculation is simply the reverse of the one above. Each mL of solution contains 0.7 mL of ethanol. Multiply by the density, and that gives you about 0.6 g per mL. Note that all of these are one-significant-figure calculations. If that's all you need, you're fine; the volume contraction will only be a few percent. If you need more precision, then you have to factor in that volume change on mixing, which means that you need to know whether the "70%" refers to the volumes mixed or to the volume fraction in the final mixture.