Sodium Rhodizonate
Definition
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 map lead distribution. Not specific to primer lead; provides supplementary spatial evidence. Applied after Modified Griess and after photographic documentation.
- Color reaction
- Deep red to scarlet complex with lead ions at acid pH
- Chemical class
- Disodium salt of 5,6-dihydroxy-5-cyclohexene-1,2,3,4-tetraone (chelating agent)
- Target evidence
- Lead distribution from gunshot entry wounds and garment holes
- Specificity confirmation
- HCl treatment converts red to purple-blue for authentic lead
Common questions
What does sodium rhodizonate do in forensic investigations?+
Sodium rhodizonate is a chemical reagent that reacts with lead ions to produce a deep red or scarlet color. Forensic investigators use it to map where lead from a bullet or bullet primer has deposited around a gunshot wound or on clothing. It is applied after photography and after the Modified Griess test to provide supplementary spatial evidence of lead distribution.
How do you confirm that the red color is actually from lead?+
When hydrochloric acid (HCl) is applied to an authentic lead-rhodizonate complex, the color shifts from red to purple-blue. This color change confirms the presence of lead. If the red color does not change, it was not a true lead reaction.
Does sodium rhodizonate tell you whether the lead came from the primer or the bullet jacket?+
No. Sodium rhodizonate reacts with lead from both the bullet primer and the bullet jacket. It shows where lead has deposited, but cannot distinguish between these two sources. That is why it is used as a supplementary test alongside other methods like the Modified Griess test.
Related terms
- Modified Griess Test
- A contact-transfer colour chemistry test for nitrite-containing propellant combustion residue. Sulphanilic acid undergoes diazotisation with nitrous acid (from NO2 on the target...
- 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...
- 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...
- 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...
- 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...
- Desensitisation (Griess Protocol)
- The step in the Modified Griess protocol in which background nitrite contamination (from sweat, atmospheric nitrogen, detergent) is removed from the garment...
- GFAAS (Graphite Furnace AAS)
- An AAS configuration using an electrically heated graphite furnace to atomise the sample, achieving approximately 100-fold lower detection limits than flame AAS....
- ICP-MS (Inductively Coupled Plasma Mass Spectrometry)
- A bulk elemental quantification technique that dissolves the entire hand swab or SEM stub and measures total element mass per sample. Complements...
- Lead-Free Primer
- A primer composition that omits lead styphnate, using DDNP or other compounds, producing no lead from the primer channel during discharge. Examples...
- NAA (Neutron Activation Analysis)
- A nuclear analytical technique in which sample irradiation in a research reactor converts stable isotopes to radioactive ones, which are identified by...
- NEDA (N-(1-Naphthyl)ethylenediamine Dihydrochloride)
- The azo coupling component in the modified Griess test. After diazotisation of sulphanilic acid with nitrous acid, NEDA couples with the diazonium...
Explained in these topics
- Firing Distance Chemistry: Griess Test and Sodium RhodizonateThe disodium salt of 5,6-dihydroxy-5-cyclohexene-1,2,3,4-tetraone. Reacts with Pb2+ ions to produce a deep red complex, used to map lead deposition around a fi...
- Instrumental GSR Analysis: SEM-EDS, AAS, NAA and Modified GriessA chelating agent producing a scarlet-to-red colour with lead ions at acid pH. Applied to entry-wound margins and garment entry holes to map lead distribution....
- Powder Tattooing, Stippling, Blackening and the Modified Griess TestA colorimetric reagent that reacts with lead ions from bullet jacket and primer to produce a red-purple complex on fabric or skin, used as a complementary test...