Chromatography — Flashcards & Quiz

Key Points

• Two phases: stationary (solid or liquid on a solid support) and mobile (liquid or gas carrying the sample).
• Separation principle: components with stronger affinity for the stationary phase move slowly; those with stronger affinity for the mobile phase move quickly.
• TLC (thin-layer chromatography): stationary = silica gel on a plate; mobile = solvent moving up by capillary action. Results shown as spots at different heights.
• Retention factor Rf = distance moved by component / distance moved by solvent front. Each compound has a characteristic Rf in a given system.
• HPLC (high-performance liquid chromatography): automated, high-pressure system; gives a chromatogram with peaks at specific retention times. Peak area is proportional to concentration.
• Calibration: use standards of known concentration to build a calibration curve, then read the unknown concentration from its peak area or height.

Common Mistakes to Avoid

1. Confusing stationary and mobile phases — stationary doesn't move, mobile does.
2. Claiming Rf depends on the compound alone — it depends on the solvent and stationary phase too.
3. Using peak HEIGHT instead of peak AREA for concentration (area is more reliable).
4. Forgetting that calibration is essential for quantitative HPLC analysis.
5. Mixing up retention time (HPLC, gas) with Rf (TLC) — both relate to separation but are measured differently.

Exam Strategy

VCAA Unit 4 AOS 2 chromatography questions give you a chromatogram and ask you to identify components or calculate concentrations. Method: (1) identify the technique (TLC vs HPLC), (2) for TLC, calculate Rf for each spot and compare to reference values, (3) for HPLC, read retention times and peak areas, use a calibration curve to convert to concentration.

Revision Tip

Chromatogram reading is a pattern skill — drill a Revizi deck with both TLC and HPLC data asking you to identify components and calculate quantities.

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