Modified Griess Test
Definition
A contact-transfer colour chemistry test for nitrite-containing propellant combustion residue. Sulphanilic acid undergoes diazotisation with nitrous acid (from NO2 on the target surface), then couples with NEDA to produce an orange-pink azo dye. Maps propellant residue distribution around a firearm entry wound.
- Detects
- Nitrite ions from smokeless powder and propellant residues
- Color result
- Orange to pink azo dye pattern
- Method
- Contact transfer of residue onto filter paper or garment, treated with reagents
- Modern status
- Current standard nitrite-pattern test, replaces classical Walker test
Common questions
What does the Modified Griess test detect?+
It detects nitrite ions left behind by propellant residues. When a firearm is discharged, particles containing nitrogen oxides settle on clothing or surfaces nearby. The test uses sulphanilic acid and alpha-naphthylamine reagents to turn these nitrites orange or pink, making the residue visible.
How does it help with firing distance cases?+
The test produces a visible color pattern that maps where residue landed around a gunshot wound. By comparing this pattern to test firings at known distances, an examiner can estimate how far the gun was from the target. It replaced the older Walker test in modern labs.
What's the chemistry behind the color change?+
Sulphanilic acid undergoes diazotisation when it meets the nitrogen oxides on the target. It then couples with alpha-naphthylamine or a similar compound to form an orange-pink azo dye. This dye only appears where nitrite particles actually landed.
Related terms
- Sodium Rhodizonate
- A chelating agent producing a scarlet-to-red colour with lead ions at acid pH. Applied to entry-wound margins and garment entry holes to...
- Azo Dye
- A class of organic dyes containing one or more azo groups (R-N=N-R'). Formed in the Griess test by coupling of a diazonium...
- Powder Tattooing
- Stippling pattern of unburned and partially burned propellant grains embedded in the skin around an entry wound. Cannot be wiped off. Pathognomonic...
- Sodium Rhodizonate Test
- Colour test for lead. The cloth is treated with sodium rhodizonate followed by buffer; lead deposits give a pink-to-red colour, confirmed with...
- Soot (Blackening)
- Submicrometre carbon-rich particles from incomplete propellant combustion, deposited on the garment or skin surface around the entry hole at contact and near-contact...
- AAS (Atomic Absorption Spectrometry)
- An analytical technique measuring the absorption of element-specific wavelengths by atomised sample. For GSR, it quantifies dissolved Pb, Ba and Sb in...
- ASTM E1588
- ASTM International standard practice for gunshot residue analysis by scanning electron microscopy with energy-dispersive spectrometry. Defines particle classification (characteristic, consistent-with, indicative), morphology...
- BSA 2023 (Bharatiya Sakshya Adhiniyam)
- India's evidence statute enacted in 2023, replacing the Indian Evidence Act 1872. Sections 39-46 govern expert testimony, including the admissibility and presentation...
- Bullet Wipe
- Greyish to brownish ring of lubricant, lead and copper rubbed off the bullet onto the margin of an entry hole in clothing....
- Contact Shot
- Muzzle pressed against skin or clothing at the moment of firing. Hallmarks are a stellate (star-shaped) wound from sub-dermal gas tracking, a...
- Contact Wound
- A firearm wound produced when the muzzle is pressed against or within a few centimetres of the target surface. Characterised by a...
- DeHaan Modification
- A refinement of the Griess test procedure for forensic propellant residue detection, using a combined sulphanilic acid + NEDA reagent on filter...
Explained in these topics
- Firing Distance Chemistry: Griess Test and Sodium RhodizonateA contact-transfer colour chemistry test for nitrite-containing propellant combustion residue. Sulphanilic acid undergoes diazotisation with nitrous acid (from...
- Determination of Range of Firing in Firearm CasesCurrent standard nitrite-pattern transfer test. Filter paper treated with sulphanilic acid plus alpha-naphthol (or N-1-naphthylethylenediamine) gives orange sp...
- Forensic Analysis of Explosives and Post-Blast ResiduesColor test for nitrites (NO2-). Sulphanilic acid is diazotised by the nitrite, then coupled with alpha-naphthylamine to give a pink azo dye. Indicates smokeles...
- Gunshot Residue (GSR) Analysis: Detection MethodsCurrent screening test for nitrites on filter paper. Sulphanilic acid plus alpha-naphthylamine reagent gives a pink to orange azo-dye colour where nitrite part...
- Instrumental GSR Analysis: SEM-EDS, AAS, NAA and Modified GriessA colourimetric test for nitrite ions applied to a garment via cellulose acetate contact transfer. Produces a pink-red azo dye at nitrite deposits; the spatial...
- Powder Tattooing, Stippling, Blackening and the Modified Griess TestA colorimetric chemical test using sulfanilic acid and alpha-naphthylamine (or a REACH-compliant equivalent) to detect nitrite ions from propellant residues on...