What does the Ninhydrin reagent primarily detect?

Ninhydrin is a chemical reagent that is widely used in analytical chemistry to detect primary amines. When ninhydrin reacts with primary amines, it forms a colored complex that can be detected visually or measured spectrophotometrically. This property makes ninhydrin particularly useful in various applications, such as protein analysis and amino acid detection.

The interaction of ninhydrin with primary amines is characterized by the release of a distinctive blue or purple color, known as Ruhemann's purple, which indicates the presence of free amino groups. This reaction is significant because it provides a method for identifying and quantifying amino acids and proteins, which are fundamental biomolecules in biological systems.

In contrast, the other options do not react with ninhydrin in the same manner. Carboxylic acids do not yield a color change with ninhydrin, making them undetectable through this method. Trichlorinated compounds and barbiturates also do not produce a reaction with ninhydrin that would indicate their presence. Therefore, the specificity of ninhydrin for primary amines establishes it as a critical tool in biochemical and analytical applications.