Which type of chromatography uses silica gel or alumina on a card as the stationary phase?

• A. Gas Chromatography
• B. Thin Layer Chromatography (TLC)
• C. Ion Exchange Chromatography (IEC)
• D. High-Performance Liquid Chromatography

Answer: (B)

The concept being tested is planar chromatography, where separation happens on a flat surface rather than inside a tube. In thin-layer chromatography, the stationary phase is a very thin layer of silica gel or alumina coated onto a card or plate (often glass, plastic, or aluminum). A small spot of sample is applied near one edge, and a solvent (the mobile phase) travels up the plate by capillary action. Components separate because they interact differently with the polar stationary phase: more polar substances stick to the silica or alumina and move slowly, while less polar substances travel farther with the solvent front.

This is distinct from gas chromatography, which uses a gas as the mobile phase and a long packed or capillary column; and from high-performance liquid chromatography, which uses a liquid mobile phase pushed through a column under high pressure. Ion exchange chromatography relies on charged resin to separate ions, not a thin layer on a plate. So the use of silica gel or alumina on a card as the stationary phase is characteristic of Thin Layer Chromatography.