Unit 23
Separations and chromatography
Real samples are almost always mixtures: separate first, then measure. This unit starts from the partition equilibrium in a separating funnel — why several small extractions beat one large one and how pH decides where an acid or a base goes — then chains extractions into a column to meet retention factors, selectivity, plate height and resolution, and ends at the controls of gas and liquid chromatographs, measuring blood alcohol with an internal standard.
- 1 Extraction: partition equilibria and the separating funnel Iodine is yellow-brown in water, but one shake with hexane turns the top layer violet. The partition coefficient tells you how much each extraction removes, why several small portions win, and how pH makes an acid or a base change layers. 25 min
- 2 Chromatography principles: retention, selectivity and Rf Repeat an extraction hundreds of times and you have chromatography. Molecules shuttle between the mobile and stationary phases, and the retention factor k sets their pace; separate leaf pigments on a thin-layer plate and read their Rf values. 25 min
- 3 Column efficiency: plates, band broadening and resolution Bands spread as they travel. Plate height, the van Deemter curve and the resolution equation show why doubling the column improves resolution by only 41 % — and why changing selectivity is usually the better lever. 30 min
- 4 Gas and high-performance liquid chromatography Oven temperature, carrier gas, stationary phase, mobile-phase strength and gradients: separate five solvents and a set of preservatives on the simulator, then use an internal standard to turn peak areas into blood-alcohol results. 35 min
- 5 Capillary electrophoresis No stationary phase, only a field: ions race along a narrow tube according to their mobilities. Mobilities and diffusion coefficients follow from ionic conductivities, electro-osmotic flow sweeps everything to the detector, and hundreds of thousands of plates pull apart even very similar ions. 25 min