Nickel nitrate is a secondary reagent used to enhance latent fingerprints initially developed with ninhydrin. Ninhydrin reacts with amino acids in fingerprint residue, producing a purple color (Ruhemann's purple). Nickel nitrate can further enhance the visibility of these developed prints, particularly on porous surfaces like paper. It reacts with the Ruhemann's purple, changing the color to a dark blue or blueish-black, often increasing contrast and detail.
Equipment
- Fume Hood: Critical for safety due to the potentially harmful fumes released.
- Glass Beakers or Flasks For mixing and storing the solution.
- Glass Spray Bottle: For applying the reagent to evidence.
- Personal Protective Equipment (PPE): Lab coat, gloves, safety glasses/goggles (or a face shield) are a must.
Ingredients and Mixing a 1-Liter Solution
- Nickel Nitrate Hexahydrate: 3 grams
- Ethanol (95% or higher): 950 mL
- Glacial Acetic Acid: 50 mL
Mixing Procedure
- Donning PPE: Put on your lab coat, gloves, and eye protection.
- Fume Hood Prep: Ensure the fume hood is functioning properly.
- Measure and Combine: In a glass beaker or flask, measure out the nickel nitrate hexahydrate, ethanol, and glacial acetic acid.
- Stir Thoroughly: Use a magnetic stir bar and stir plate, or swirl the solution manually, until the nickel nitrate is fully dissolved.
- Transfer to Storage: Carefully pour the mixed solution into a labeled, amber glass bottle for storage.
Latent Print Development with Nickel Nitrate
- Primary Development: The latent prints must first be developed using ninhydrin. Follow standard ninhydrin processing procedures.
- Fume Hood: Work inside a fume hood for ventilation.
- Application: Lightly spray the ninhydrin-developed prints with the nickel nitrate solution. Avoid heavy application that might obscure detail.
- Reaction: Allow the nickel nitrate to react with the Ruhemann's purple. The color change should be visible within a few minutes.
- Documentation: Photograph the enhanced latent prints promptly for records and analysis.
Storage Requirements
- Amber Glass Bottle: Protects the solution from light degradation.
- Tightly Sealed: Prevent evaporation and contamination.
- Cool, Dry Location: Storage away from heat and direct sunlight is essential.
- Proper Labeling: Include the solution contents, preparation date, and any hazard warnings.
Shelf Life
The shelf life of nickel nitrate solution can vary depending on storage conditions. However, it's generally considered to have a shelf life of about 6-12 months when stored correctly. Always check for any signs of degradation (like discoloration or precipitation) before use.
Important Notes:
- Nickel nitrate is considered a hazardous substance. Please consult the Safety Data Sheet (SDS) for full safety information and disposal guidelines.
- Nickel nitrate is a secondary, enhancing reagent – it won't develop prints on its own.
- Experimentation with different concentrations or variations with other solvents may be done by experienced examiners, with careful documentation.