Examination of Firearms Review: 2007 to 2010 - Interpol

Other reagents
Lawsone (2-hydroxy-1,4-naphthoquinone) is a new amino acid reagent that has been
proposed by Jelly et al. to detect fingermarks on porous substrates (225). The
reaction of lawsone with latent secretions leads to purple-brown marks that are also
luminescent. However, only preliminary results on filter paper were presented, and
further research is required to assess the quality of this reagent compared with 1,2indanedione
or DFO.
Isatin (1H-indole-2,3-dione) is structurally similar to ninhydrin or 1,2-indanedione and
has consequently been proposed as a new amino acid reagent able to detect latent
fingermarks (226). For this study, six donors were asked to leave fingermarks on
white paper. The marks were aged during two days before being processed. The
composition of the working solution, the development conditions, and the use of
metal salts (i.e. zinc acetate, zinc chloride, and zinc nitrate) in the working solution or
as post-treatments were studied. The authors concluded that a 0.05% (w/v) of isatin
in 12.5% (v/v) acetone, 87.5% (v/v) dioxane and carbonate buffer gave the most
intense luminescence, but with a less intensely coloured product. The development
conditions were similar to those recommended for 1,2-indanedione, the samples
being heated at 180°C for 10 s. The samples could subsequently be post-treated by
dipping them in an ethanolic zinc chloride solution, and reheating them at 180°C for
10 s. When compared with DFO and 1,2-indanedione/zinc on half-cut fingermarks,
isatin consistently showed lower luminescence intensity and greater unwanted
background luminescence. When compared with ninhydrin, isatin consistently gave
no coloured fingermarks. These results illustrate the fact that further research is still
required before proposing isatin as an alternative to the classical amino acid
reagents.
Para-dimethylaminocinnamaldehyde (pDMAC) has for long been considered as a
reagent able to detect latent fingermarks by targeting urea contained in the
secretions. A recent study performed by Lee et al. tends to prove that pDMAC is not
reacting with urea but rather with amino acids (227). When compared with classical
amino acid reagents to detect fingermarks on thermal papers, such as ninhydrin and
DFO, pDMAC was shown to be far less effective in terms of colour and
luminescence. Consequently, its use is not recommended.
2.2.3 Cyanoacrylate fuming
The possibility to rejuvenate old fingermarks to improve the cyanoacrylate
fuming process has been investigated, and led to the conclusions that the
items should be exposed to either acetic acid (229) or methylamine
vapours (230). The role played by the environmental pH on the
morphology and length of the polymer chains has also been investigated
(231). An attempt to optimize the fuming time when processing
fingermarks on skin failed in determining optimal conditions (232). Finally,
a detrimental effect of cyanoacrylate fuming has been observed if the
items (latex/nitrile gloves or duct tapes) have to be subsequently
processed by powder suspensions (233).
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