DFO: An alternative to Ninhydrin
Several very effective methods are available for latent print development on porous materials. Iodine fuming was discussed in PrinTips-02. This article will cover DFO (1,8-Diazafluorene-9-one), which is a Ninhydrin analog, and it too reacts to amino acid residues in latent prints.
Ninhydrin has been a mainstay for latent print development for several decades. Its original development was to serve as a dye stain for examining body cells under a microscope. It reacts to the presence of amino acids by producing a purple stain.
But Ninhydrin has its shortcomings, namely, that developed prints may be difficult to see—let alone photograph. The addition of zinc chloride solution adds fluorescence to weak prints.
In 1989, researchers with the Department of Chemistry, Belfast, Northern Ireland (per the FBI) introduced DFO, which is now commercially available and used in the United Kingdom. Unlike ninhydrin, DFO gives a weakly colored initial print; the main feature of this reagent is its ability to give a fluorescent print without secondary treatment.
DFO is said to produce 2.5 times the number of latent prints than Ninhydrin. The most often used formula for DFO is as follows:
DFO STOCK SOLUTION
1 gm DFO crystals
200 ml Methanol
200 ml Ethyl Acetate
40 ml Glacial Acetic acid
Combine and stir with a magnetic stirrer until ALL the ingredients are dissolved.
DFO WORKING SOLUTION
Add Petroleum ether to the stock solution until the total volume is two liters.
Keep in mind that the DFO prepared working solution has a relatively short shelf life, so this two-part formula will assure that the maximum benefit will be achieved.
Procedure:
1. Saturate both sides of the document or evidence to be examined. Allow the
evidence to air dry.
2. Place evidence in a heat chamber (DFC100) preheated to 200º F.
3. Remove the evidence after having been exposed to heat for 5-10 minutes.
4. Examine the item for any visible prints. generally, DFO prints will not be immediately visible. if any prints are visible, they will be pale pink in color.
5. Examine the evidence in a darkened room using long-wave ultraviolet light or
an alternate light source.
6. Photograph any visible latents while exposed to UV or alternate light source. Be certain to include a scale in each photo. Note: DFO treatment will not interfere with subsequent chemical tests.
Learn more from the Technical Bulletin: “Overview of Latent Print Development Techniques”
http://www.sirchie.com/Assets/Manuals/pdf/LP%20Dev'mt%20Tech_TB02-102ENG-REV2E.pdf
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