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JEE Main · 2022 · 28 Jun 2022 · Shift 1 · Practical and Analytical Chemistry

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Which one of the following techniques is not used to spot components of a mixture separated on thin layer chromatographic plate?
  1. (A) (Solid)
  2. (B)U.V. Light
  3. (C)Visualisation agent as a component of mobile phase✓ Correct
  4. (D)Spraying of an appropriate reagent

Answer: (C)

Solution

In thin-layer chromatography (TLC), after separation, spots are visualized using:
  • Iodine vapor ( solid): sublimes and adsorbs onto organic compounds, making them visible as brown spots.
  • UV light: many compounds fluoresce or absorb UV, allowing visualization on fluorescent TLC plates.
  • Spraying reagents: specific chemical reagents (e.g., ninhydrin for amino acids, for charring) are sprayed to develop colored spots.

A visualization agent as a component of the mobile phase is NOT used. The mobile phase is the solvent system that carries compounds up the plate during separation; visualization agents are applied after separation, not mixed into the mobile phase.

Therefore, option (C) is not a technique used for spotting components.

JEE Main · 2022 · 28 Jun 2022 · Shift 1 · Single correct option

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