Which technique uses an iodine vapor chamber for visualization?

• A. Paper chromatography
• B. Thin-Layer Chromatography
• C. Column Chromatography
• D. Diafiltration

Answer: (B)

Iodine vapor visualization relies on iodine forming colored complexes with many organic compounds, making spots visible after chromatographic development. In thin-layer chromatography, the plate has a very thin stationary phase on a solid support, so some spots may be colorless after development. Exposing the plate to iodine vapor allows iodine to adsorb onto the compounds on the surface, producing brownish to yellow-brown spots that you can see without applying stains or UV light. This method is simple, quick, and gentle, and it’s a classic way to reveal separations on TLC plates. The other techniques listed are not typically associated with this visualization method: diafiltration is a membrane-based purification process, and column chromatography is a preparative separation not involved with iodine visualization in the same way. Paper chromatography can be visualized by various methods, but the iodine vapor chamber is most characteristically used with thin-layer chromatography.