We have an amino acid in the form of a salt with trifluoroacetate, and the side chain is not charged. We do not presently known the identity of the impurities. We are planning to try chromatography on Dowex-1 in the acetate form, but for a related molecule that we are also working on, we think that Dowex-based resins would be a poor choice. Therefore, we are looking at alternatives. We have some C18-silica with a 40 µm particle size. We also have a few C18-TLC plates that could be used for method development, but I have never run a gravity or flash column with this solid phase before. Would it be reasonable to try a column-based approach? Does anyone have a recommendation for a book which discusses this technique? I checked Advanced Practical Organic Chemistry (Leonard) and Practical Organic Synthesis (Keese), but I did not see anything.
If not, what should we be using, Dowex-50, and eluting with HCl? We want to avoid the classical method of elution from Dowex-50, in which the amino acid is eluted with ammonia. Some years ago we worked out a way to purify amino acid derivatives with charged side-chains using a volatile buffer and Sephadex-based matrices near pH 8, but I don't see that method being useful in this instance, owing to the lack of a charged side chain.