Pauly's Test For Histidine And Tyrosine

Pauly's test is a chemical test to detect the amino acid histidine and tyrosine. The basic principle in pauly's test is diazotized. Sulfanilic acid will be diazotized with the addition of sodium nitrite and sodium carbonate. Sulfanilic acid that has diazotized will form diazonium component. Diazonium component react with the imidazole ring of histidine and a phenol group of tyrosine to form dark red compound.

Diazotisation is a reaction between an aromatic amine (in this case sulfanilic acid) with sodium nitrite and sodium carbonate to form diazonium component. Diazonium component only form in cold conditions.

Histidine

Tyrosine

Summary reaction:

• Sulfanilic acid + sodium nitrite + sodium carbonate = diazonium component
• Diazonium component + (imidazole ring of histidine / phenol group of tyrosine) = dark red color solution

Material and reagents:

• Material to be tested
• Sulfanilic acid
• Sodium nitrite (NaNO2) (0.05%)
• Sodium carbonate (NaCO3) (0.001%)

Work steps:

• Put 2 ml of material to be tested in a test tube, cooled in ice box.
• Add 1 ml of sulfanilic acid, remain in the ice box.
• Add 1 ml of sodium nitrite, let cool for 3 minutes.
• Add 2 ml of sodium carbonate.
• Observe the color changes.

Note:

Diazonium component only formed in a cold condition, so that the use of ice is needed.

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