In chromatography, why is a locating agent used when amino acids are studied?

• A. To detect colorless amino acids
• B. To speed up the process
• C. To change pH
• D. To dry the sample

Answer: (A)

In chromatography, you need to be able to see where the separated amino acids have moved, and many amino acids are colorless on the plate. A locating agent reacts with the amino acids to produce visible colors, so each spot becomes easy to detect and measure. For example, ninhydrin reacts with amino groups to give a purple color, revealing where each amino acid is. This visualization is essential for determining how far each compound traveled (Rf values) and for identifying them. The locating agent isn’t about speeding up the separation, changing the pH, or drying the sample. It’s specifically for making the colorless amino acids visible after they’ve been separated.