[ygul]

How can I determine the purity of a compound (small molecule ~300 Da) I have purified?

[Arkcon]

That would depend greatly on the general physical and chemical properties of the pure substance you believe you have.  You really can't expect a useful answer without giving us some of that information.

[ygul]

That would depend greatly on the general physical and chemical properties of the pure substance you believe you have.  You really can't expect a useful answer without giving us some of that information.

It is vicine. Density, 2.18. Melting point, 242-244 ºC.
UV detectible at specific wavelengths in acid, base, and neutral buffer and I know the related extinction coefficients.

 http://www.chemblink.com/products/152-93-2.htm

[Arkcon]

When I'm confronted by a large organic molecule, often with nitrogenous rings, of the sort that usually have a biological effect, such as this one, I immediately think -- "analysis by reverse-phase HPLC."  A quick Google for "vicine HPLC" gave me these two references: 

http://pubs.acs.org/doi/abs/10.1021/jf00082a020
http://www.ncbi.nlm.nih.gov/pubmed/7659704

How do those two work for you?  You've mentioned some physical stats that can't really be used to identify and quantify slightly similar impurities in a mixture.  So I don't know what your plan is.

[tomek]

Melting point can also give you some information. If it's sharp you can infer you substance is reasonably pure, if it's broad then there is probably something wrong. Simple TLC should also provide answer if there's impurity present. Also don't forget about NMR which is great quantification tool if used properly.

[Arkcon]

Yep, like tomek: said, if you just want to know if your compound is pure, melting point is a good way to go.  UV-Vis doesn't really give good information in that regard, it can't differentiate between similar compounds, usually.  And of course, TLC is much less expensive than HPLC.

[ygul]

When I'm confronted by a large organic molecule, often with nitrogenous rings, of the sort that usually have a biological effect, such as this one, I immediately think -- "analysis by reverse-phase HPLC."  A quick Google for "vicine HPLC" gave me these two references: 

http://pubs.acs.org/doi/abs/10.1021/jf00082a020
http://www.ncbi.nlm.nih.gov/pubmed/7659704

How do those two work for you?  You've mentioned some physical stats that can't really be used to identify and quantify slightly similar impurities in a mixture.  So I don't know what your plan is.

That would depend greatly on the general physical and chemical properties of the pure substance you believe you have.  You really can't expect a useful answer without giving us some of that information.

It is vicine. Density, 2.18. Melting point, 242-244 ºC.
UV detectible at specific wavelengths in acid, base, and neutral buffer and I know the related extinction coefficients.

 http://www.chemblink.com/products/152-93-2.htm

first reference could help