Triphenylmethane Dye
Definition
A class of synthetic dyes built around a central carbon bonded to three phenyl groups. Members include malachite green, crystal violet, and fuchsin. Many are electrochromic, existing in both coloured and colourless redox states.
- Structure
- Central carbon bonded to three phenyl groups
- Members
- Malachite green, crystal violet, fuchsin
- Property
- Electrochromic, coloured and colourless redox states
- Forensic link
- Basis of the leucomalachite green presumptive blood test
Common questions
How does the electrochromic property of triphenylmethane dyes make the leucomalachite green test work?+
The leuco (colourless, reduced) form of the dye is oxidised by haemoglobin's peroxidase-like activity in the presence of hydrogen peroxide, converting it to the coloured form, so a colour change signals a presumptive positive for blood.
Does a positive triphenylmethane-dye based blood test confirm the stain is human blood?+
No. These are presumptive tests that react to peroxidase-like activity from many sources, including some plant materials and animal blood, so a positive result must be followed by a confirmatory and species-specific test.
Related terms
- Cross-Checking
- The practice of running two different presumptive tests on adjacent cuttings from the same stain. Concordant results (both positive or both negative)...
- Leucomalachite Green (LMG)
- The reduced, colourless form of malachite green. It is oxidised to the coloured malachite green form by active oxygen released when haemoglobin...
- Malachite Green
- A synthetic triphenylmethane dye with an intense blue-green colour in its oxidised form. It is a common industrial dye and the coloured...
- Presumptive Colour Test
- Any rapid field or laboratory test that produces a colour change in the presence of a target substance. Positive results are indicative,...
- Substrate Control
- A sample of the unstained surface material from an area adjacent to a body fluid stain, collected alongside the stain and processed...