I'm a freshman and I recently learned how to do TLC and column chromatography. I also know a little about other ways to separate things by chromatography, such as affinity chromatography, gel chromatography, ion exchange chromatography, and gas chromatography, but without many details.
I am facing problems in solving a question requiring us to judge how to separate these combinations of substances by chromatography (if there was no such confinement, this will be much easier):
- N-phenylethanamide, N-phenylpropionamide
- methoxymethane, ethoxyethane
- Aβ36，Aβ42 (Aβ is a kind of peptide which is related to Alzheimer's disease, while the number, 36 and 42, refer to the amount of amino acids polymerized in the peptide)
Here are the specific issues I've met：
- I've no idea how to deal with the first combination since their difference seems to not be significant, no matter in polarity, acidity (basicity), or molecular size. Is there any other chromatographic way, or did I get something wrong?
- I think I can deal with the second combination by gas chromatography, since they are both volatile. But I'm not sure if it is a good idea. Is there a better way or not?
- I've found some description for the separation of different Aβ, suggesting that the following ways are usually used: use antibodies (e.g. ELISA) or electrophoretic separation (e.g. PAGE). But seems that neither ways are related to chromatography. It is also said that reverse phase liquid chromatography after CNBr cleavage works, but this way is complex and time consuming. I'm wondering (a) if I can use antibodies or something else to deal with it by affinity chromatogrphy and (b) how CNBr works? (Now I know CNBr is used to cut proteins/peptides at where methionines are, but still not knowing how reverse phase liquid chromatography works.) Also I want to ask if there is a better way as well.