[ScardyBob]

As the title says, I've run into a problem using data from a paper because they specify concentrations in % and ppm, but don't say whether its by mass or by mole. My understanding is that different fields use different conventions when the basis isn't specified, so I'm hoping someone with experience in this area will point me in the right direction.

The paper in question is here: http://pubs.acs.org/doi/abs/10.1021/ie50496a058

It's an old article (from 1951) on the oxidation of propanal to propionic acid. My initial intuition is that its likely by mass, but since they use both grams and moles in the article, I can't be sure they didn't presume everything on a by mole basis.

Any thoughts?

[Babcock_Hall]

That is a vexing question, and I would defer to others here with greater knowledge of analytical chemistry.  However, if I were forced to make a decision about a solution of a solid into a liquid solvent, I would assume that a number in percent meant grams of solid in 100 mL of solution.  Mileage may vary, so let's hear what others have to say.

[discodermolide]

Usually it is weight %, that is w/w.
 

[ScardyBob]

w/v does sound reasonable for a solid in solution, so that may just be what I assume. They also give the amount of water used as a % of the aldehyde input (no basis specified), which I'm inclined to assume as w/w.

Thanks for the *delete me*

[AWK]

% refers always to w/w as a default for solids and liquids. The only exception is for ethanolic solutions for which v/v is a default. Also for gaseous mixtures v/v is a default. ppm is derived from mass fraction, and only for diluted water solutions  volume and mass of solution are numerically approximately equal.

[Arkcon]

When people find themselves vexed by this sort of problem, I often tell them:  Compute it both ways.  Do the calculations as w/w, and then as w/v.  Heck, even try v/v, or v/w if appropriate.  Or in your case, mole/mol. Then compare exactly how much is there in each case.  Maybe its not significant, for the application at hand.  Maybe the possible differences are with the typical errors of the measurement, so it likewise doesn't matter.