A gold analysis with a hydrazine test kit is based on the reduction of dissolved gold ions (Au³⁺) to elemental gold (Au⁰) by hydrazine. This precipitates fine gold powder, which can then be weighed or visually assessed. Here is a typical procedure:

1. preparation of the gold solution
• A sample containing gold (e.g. ores, alloys) is dissolved in aqua regia (HCl + HNO₃) or another suitable acid to bring gold ions into solution.
• If interfering metals are present, prior selective precipitation or separation may be necessary.
2. reduction with hydrazine
• The gold solution is prepared in a chemically stable container (e.g. glass or plastic).
• A pH adjustment may be necessary (often slightly acidic to neutral).
• Hydrazine hydrate (N₂H₄-H₂O) is slowly added to the solution. Hydrazine reduces the gold ions
• Elemental gold precipitates as a brown to black precipitate.
3. gold extraction and analysis
• The precipitate is separated from the solution by filtration or centrifugation.
• After drying, the gold can be weighed or further tested for purity (e.g. by X-ray fluorescence analysis or melting tests).

Advantages of the hydrazine test

• High selectivity for gold compared to many other metals.
• Simple handling without expensive analytical equipment.
• Visible detection reaction, as elemental gold precipitates.