Lead acetate test (Lead sulfide test): Principle, Reaction, Reagents, Procedure and Result Interpretation

Lead acetate test (Lead sulfide test)

(Detection of sulphur containing amino acids)

This test is specific for sulphur containing amino acids (Cysteine, Cystine, and Methionine)

Principle:

The sulfur-containing amino acid such as cysteine, cysteine, and methionine (sulfhydryl/thiol group) reacts with lead acetate under alkaline conditions to form a brown precipitate. These sulfur-containing amino acids are degraded in strongly alkaline media to release sulfide ion (S^2-) in the form of H₂S (hydrogen sulfide). The sulfide ions can react with lead (II) acetate to form a brownish-black precipitate.

Reaction:

Reagents:

• Test solutions:
  • Amino acids: 1 % solution of amino acids like glycine, cysteine, etc.
  • Protein solution: egg albumin in distilled water (10%)
• 40% NaOH
• 20% lead acetate

Procedure:

• To 2 ml of the test solution add 2 ml of 20% NaOH and boil for a minute.
• Cool it and add a drop of lead acetate solution.
• Observe the formation of black lead sulfide precipitate.

Note: Carry out this test in the hood if possible.

Result Interpretation:

Positive test: Formation of black precipitate indicate the presence of sulfur-containing amino acid.

Negative test: No formation of black precipitate indicate the absence of sulfur-containing amino acid.

References:

• https://www.onlinebiologynotes.com/lead-sulfide-test-detection-of-amino-acid-containing-sulfhydral-group-sh/
• glossary.oilfield.slb.com/en/Terms/l/lead_acetate_test.aspx
• http://ecoursesonline.iasri.res.in/mod/page/view.php?id=53516
• https://www.researchgate.net/publication/331609279_How_to_Test_For_Sulfur_in_Materials_Using_Lead_Acetate_Paper
• https://www.pdscholar.com/engineering/question/in-lead-acetate-test-of-sulphur-detection-lassaign/5a11adaa0a975a6b98ef72df