Question

Which one of the following techniques is not used to spot components of a mixture separated on thin layer chromatographic plate?

• A. I₂ (Solid)
• B. U.V. Light
• C. Visualisation agent as a component of mobile phase
• D. Spraying of an appropriate reagent

Answer 1

The Correct Option is C

Thin Layer Chromatography (TLC) is an analytical technique used to separate and identify components within a mixture. Visualization of spots on a TLC plate is an essential step, which can be achieved using different techniques. Let's analyze each option to determine which is not commonly used for visualization:

1. I₂ (Solid): Solid iodine crystals are commonly used to visualize compounds on TLC plates. The iodine vapors react with and brown different spots on the plate, making them visible.
2. U.V. Light: Many compounds absorb ultraviolet light. A TLC plate can be placed under a UV lamp to reveal spots that are fluorescent or UV-active. This is a standard method for visualizing components.
3. Visualisation agent as a component of mobile phase: The mobile phase is the solvent that carries the sample through the stationary phase. Visualization agents are not typically added to the mobile phase because their purpose is not to separate but to visualize components after they have been separated. Adding visualization agents to the mobile phase might interfere with the separation process.
4. Spraying of an appropriate reagent: After the separation process, a reagent can be sprayed onto the TLC plate to react with components and change their color, making them visible. This is a common post-separation technique used to highlight specific compounds.

Based on the above explanations, the technique not used to spot components is:

Visualisation agent as a component of mobile phase

This is because the mobile phase should solely focus on aiding the separation of compounds, and visualization is typically a separate process hence not a component of the mobile phase.