Ninhydrin is a chromogenic analytical probe for the quantification of proteins and amino acids.

Chromogenic analytical probe:

I. Amino Acid Analysis
1. Material Preparation
1) Ninhydrin solution: Prepared as 0.2%–1% ethanol or propanol solution.
2) Amino acid standard solution or sample to be tested.
3) Buffer: Commonly used citric acid buffer or other buffers with pH 5.5–6.5.
4) Heating equipment: such as water bath or constant temperature heating device.
2. Steps
1) Prepare the reaction system: Add a certain volume of sample solution and an appropriate amount of Ninhydrin solution (usually 1:1 of the sample volume) to the test tube.
Add buffer to adjust the reaction conditions (optional).
2) Heating color development: Heat the reaction system at 90–100°C for 10–20 minutes to generate blue-purple or yellow compounds (Ruhemann's purple).
3) Cooling and detection: Cool the reaction system to room temperature; use a spectrophotometer to measure the absorbance at 570 nm (blue-purple) or other appropriate wavelengths to calculate the amino acid concentration.
II. Protein detection
1.. Material preparation
1) Ninhydrin solution (0.5%–1% propanol solution).
2) Protein sample solution.
30 Buffer (such as phosphate buffer).
2. Steps
1) Reaction preparation: Add an equal volume of Ninhydrin solution to the sample solution and mix gently.
2) Heating color development: Heat the mixture to 90–100°C for 15 minutes. The color reaction depends on the type and concentration of amino acids.
3) Detection: After cooling, use a spectrophotometer to measure the absorbance at a specific wavelength (usually 570 nm) and use a standard curve for quantitative analysis.
Precautions
1) Operation safety: Ninhydrin is a potential allergen. Gloves and goggles should be worn during operation, and experiments should be performed in a well-ventilated area.
2) Storage in the dark: Ninhydrin is light-sensitive. The solution should be stored in the dark. It is recommended to store it at 4°C for short-term storage and -20°C for long-term storage.
3) Optimize reaction conditions: According to the characteristics of the sample, appropriately adjust the pH, temperature and reaction time to obtain the best results.

The above information is based on published literature. Experimental procedures should be appropriately modified to meet specific research demands.

DMSO: 240 mg/mL (1347.25 mM), Sonication is recommended.

H2O: 20 mg/mL (112.27 mM), Sonication and heating to 60℃ are recommended.