So, I've extracted a small amount of (hopefully) caffeine from coffee via solvent extraction with hexane. Quick note before i go on, I know that this is possibly not the best method - however I am trying to determine the best method of caffeine extraction via experiment. Anyways, to determine what is the best method, I obviously need to know the purity of my sample. I would have thought that a titration would be best? Anyone else got any other ideas? And what could I titrate against. I had thought of HCl or H2SO4, but I'm not sure if there's anything that would indicate to me the the completion of the reaction, apart from say temperature change... maybe pKa? Would anyone be able to point me in the right direction?