Chromatography Forum

How do you determine if a compound is polar or non polar?

If the compound is known, you can tell from its structure.

If the compound is unknown, you can qualitively determine its polarity chromatographically. Among many ways, you could try following:

1. Inject the compound (of course properly diluted first) to a RP C18 column in MeCN/phosphate buffer, pH7 v/v 50/50.

2. Inject the same compound to a RP C18 column in MeCN/phosphate buffer, pH3 v/v 50/50

In my opinion, if the compound can be retained sufficiently (e.g. k'>2) in either case, it is non-polar. Otherwise, it is somewhat polar.

3. To further evaluate its polarity, you can use higher organic solvent and higher aqueous content in the mobile phase. In general, the compound that requires higher than 90% aqueous in the mobile phase is considered highly polar.

Polarity is not the only factor guiding adsorption.
Polarity of a compound is a clearly defined property, check into dipole moment and maybe also polarizabilty in physical chemistry texts, the internet, . . .

some software, I believe, also makes estimations. I think ACD labs sell such stuff, but I have never used it.