A liquid sample obtained from a plant extract contains dissolved caffeine, vanillin, and an intensely colored pigment (molar mass ≈800 g mol⁻¹). All three solutes are completely miscible in water, and none are volatile below 200 °C. The researcher’s objectives are to (1) isolate caffeine in pure solid form for quantitative analysis, (2) obtain vanillin in a solution free of other solutes, and (3) preserve the colored pigment in an aqueous medium without thermal degradation.
Assume standard laboratory glassware and supplies are available, including chromatography columns, a rotary evaporator, and filtration apparatus.
(a) Describe a sequence of at least two separation steps that will accomplish all three objectives. Clearly state what is collected after each step.
(b) For every step in your sequence, identify the key physical or chemical property difference that enables separation.
(c) One proposed step involves column chromatography using a polar stationary phase and a non-polar mobile phase. Predict the elution order of the three solutes, explaining your reasoning in terms of intermolecular forces.
(d) Suggest one procedural modification that would reduce solvent usage without compromising the purity targets, and justify your suggestion.