Leucocrystal Violet (LCV) is a blood-specific reagent. It works by reacting with the heme in blood proteins (hemoglobin) to create a dark purple deposit. LCV is considered a useful presumptive test for blood as it provides increased contrast and visibility, facilitating the documentation and recovery of blood-based latent prints.
Equipment
- Spray Bottle: Preferably a fine-mist sprayer for optimal coverage and detail preservation.
- Personal Protective Equipment: Gloves, a respirator mask (hydrogen peroxide fumes), and eye protection.
- Well-Ventilated Area: LCV's components necessitate strong ventilation. Consider a spray cabinet or fume hood if available.
Ingredients for a 1 Liter LCV Solution
- Leucocrystal Violet: 1.0 gram
- Hydrogen Peroxide (3%): 200 ml
- Glacial Acetic Acid: 8 ml
- Distilled Water: 792 ml
Mixing Procedure
- Safety First: Begin in a well-ventilated workspace, donning your PPE.
- Dissolving Leucocrystal Violet: Dispense the distilled water into a clean container. Slowly, add the Leucocrystal Violet while stirring consistently to fully dissolve the powder.
- Acid Addition: Carefully add the glacial acetic acid to the solution and continue stirring.
- Hydrogen Peroxide: Finally, introduce the hydrogen peroxide, again stirring to form a homogeneous solution.
Latent Print Processing with Leucocrystal Violet
- Examination: Before applying LCV, visually inspect the surface for existing bloody prints. This establishes a baseline and prevents the loss of detail in fainter stains.
- Application: Utilizing the fine-mist sprayer, evenly apply a light coating of LCV to the desired surface. Avoid oversaturation.
- Reaction: Allow sufficient time for the reagent to react with any latent blood deposits. Typical development ranges from seconds to a few minutes.
- Documentation: Once visible, thoroughly photograph the developed latent prints with appropriate scales and lighting.
- Collection: Depending on the surface, relevant collection techniques (swabbing, lifting) for potential DNA analysis can be undertaken after photography.
Storage and Shelf Life
- Light Protection: The separate components of LCV (Leucocrystal Violet powder and hydrogen peroxide before mixing) are light-sensitive. Store in dark, opaque containers.
- Refrigeration: Ideally, store the mixed LCV solution in a refrigerator between uses.
- Shelf Life: Generally, a premixed LCV working solution has a shelf life of approximately 6-8 months, if stored correctly. It's essential to test the solution before use to ensure it retains adequate reactivity.
Important Considerations
- Porous Surfaces: LCV primarily excels on porous substrates like paper or cardboard.
- Overreaction: Prolonged exposure can lead to diffusion and a loss of fingerprint detail, particularly on porous surfaces. Monitor the development closely.
- False Positives: While it's considered a presumptive blood test, LCV can yield false positives due to reactions with oxidizers or other substances. Employ confirmatory blood tests where needed.