Why are locating agents sprayed when amino acids are investigated?

• A. Because amino acids are colourless
• B. Because amino acids are highly reactive
• C. Because locating agents speed up chromatography
• D. Because amino acids produce color

Answer: (A)

In chromatography, you need to be able to see where each substance has moved. Amino acids often don’t have any color by themselves, so their spots would be invisible on the plate. Spraying with a locating agent introduces a chemical reaction that produces a visible color at each amino acid spot (for example, ninhydrin forms a purple color with amino acids after heating). That’s why the spray is used: to reveal colorless amino acids so you can track and compare their positions.