Ninhydrin is a classical reagent that is almost always present in biochemistry and analytical chemistry laboratories. The compound is the hydrated form of indane-1,2,3-trione and is widely known for its characteristic reaction with amino acids and primary amines, producing a deep purple substance popularly referred to as Ruhemann's purple. That reaction forms the basis of the qualitative test for the presence of amino acids, spot detection in thin-layer chromatography, and quantitative determination by spectrophotometry. Its role is simple yet essential: it converts colourless, invisible compounds into a clear visual signal that is easy to read.
The properties that make ninhydrin the preferred choice are its high sensitivity toward free amino groups and the intense, consistent colour of its reaction product. Proline and hydroxyproline, which are secondary amines, give a yellow colour instead, so the user simultaneously obtains information that distinguishes between types of amino acids. Its physical form is a crystalline solid that dissolves readily in ethanol, acetone, or butanol for the preparation of spray solutions as well as test solutions. Ninhydrin is sensitive to light and air, so prepared solutions should be stored appropriately and used within a reasonable period.
In Indonesian laboratories, ninhydrin is routinely used across university teaching laboratories, food and agricultural testing facilities, and research groups working on proteins and peptides. It appears in practical classes demonstrating amino acid identification, in chromatography work where spots must be visualised after development, and in quality control settings where free amino nitrogen is measured. Because it is used in small quantities per test, a single package typically supports a large number of analyses over an extended working period.
TCI brochures (PDF)
- Titration Reagents and TLC Stains 2026-05-07 · p. 12
- Qualitative amino acid testing — the reagent reacts with free amino groups to generate Ruhemann's purple, giving an unambiguous visual confirmation that amino acids are present in a sample.
- Thin-layer chromatography spot detection — after development, spraying the plate with a ninhydrin solution reveals otherwise colourless amino acid spots, allowing positions and relative migration to be recorded accurately.
- Spectrophotometric quantification — the intense and consistent colour of the reaction product allows amino acid concentration to be determined by absorbance measurement against a prepared calibration series.
- Differentiation of primary and secondary amines — proline and hydroxyproline give a yellow colour rather than purple, so the analyst gains structural information about the amino acid alongside simple detection.
- Protein and peptide research support — the reagent is used to monitor free amino groups released during hydrolysis or enzymatic digestion, making reaction progress visible without specialised instrumentation.
| Brand | TCI |
|---|---|
| CAS number | 485-47-2 |
| Molecular formula | — |
| Purity | — |
| Category | Chemistry > Building Blocks > Non-Heterocyclic Building Blocks |
| Pack sizes | available in standard TCI catalogue packaging; please confirm the required size when ordering |
| Physical form | crystalline solid, soluble in ethanol, acetone, or butanol |
| Storage | sensitive to light and air; keep containers closed and protected from light |
Store ninhydrin in a tightly closed container in a cool, dry place away from direct light, since the compound is sensitive to both light and air. Amber glass bottles or the original supplier container are suitable; prepared solutions should also be kept protected from light and used within a reasonable working period rather than held indefinitely. Handle the solid in a well-ventilated area or fume hood, wearing gloves, safety glasses, and a laboratory coat, as the reagent stains skin and clothing readily on contact. Avoid generating dust during weighing, keep the material away from strong oxidising agents, and clean any spills promptly. Always consult the manufacturer's safety data sheet before use.
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