During a thin-layer chromatographic (TLC) analysis of a reaction mixture, a student observes that the spot corresponding to compound A is elongated and exhibits significant tailing, whereas other spots remain compact. Compound A contains both an amide group and a tertiary amine within the same molecule.
(a) Explain, at the molecular level, why tailing is more likely for compound A than for the other components of the mixture. Your answer should consider specific types of interactions with the stationary phase surface.
(b) Propose two experimental modifications that would reduce tailing for compound A, and explain the chemical basis for how each modification would alleviate the problem.
(c) Compound A must ultimately be isolated in pure form. Describe a chromatographic or non-chromatographic technique that could follow TLC to achieve preparative-scale separation, and justify why it is suitable given the polarity profile of compound A.