Collect spent eluents in appropriate hazardous waste (halogenated vs non‑halogenated); discard stains/iodine as hazardous liquid waste; place used TLC plates in solid chemical waste; keep containers closed and labeled.
Equipment & Chemicals
TLC plates (silica), capillary spotters, covered chambers with filter‑paper wick, UV lamp (254 nm), forceps, ruler, pencil; melting point apparatus and closed‑end capillaries; standards (acetaminophen, aspirin, caffeine, ibuprofen); unknown solution; eluents (hexanes, ethyl acetate, 1:1 hexanes:EtOAc); iodine or approved stains as assigned.
Procedure
A. TLC (Find the Best Eluent)
1. Prepare three covered chambers (hexanes; ethyl acetate; 1:1 hexanes:EtOAc). Line each chamber with filter paper; ensure the solvent level is below the pencil baseline on the plate.
2. Draw a baseline ~1.0 cm from the bottom and a top mark ~1.0 cm from the top. Label lanes clearly in pencil.
3. Spot small (1–2 mm) dots of standards and the unknown on the baseline; allow to dry; re‑spot to concentrate without spreading (keep ≥0.5 cm between spots and edges).
4. Develop each plate; remove when the solvent is ~5–10 mm below the top mark. Immediately mark the solvent front and dry the plate.
5. Visualize under 254 nm UV; circle spots. Apply iodine/chemical stain only if needed, then circle spots again.
6. Select the eluent that produced the clearest resolution and compute Rf for all analytes on that plate.
B. Melting Temperature (Standards and Unknown)
1. Finely powder the sample and load 3–4 mm into a closed‑end capillary.
2. Heat rapidly to ~10 °C below the expected mp, then at 1–2 °C/min; record onset and clear‑point (melting range). Cool before the next run.
3. Run acetaminophen, aspirin, caffeine, and ibuprofen; then run the unknown (quick estimate followed by a precise run).