Dermal Nitrate (Paraffin) Test
Definition
Historical test where molten paraffin was cast on the suspect's hand and the cast was sprayed with diphenylamine in sulphuric acid. Blue colour indicated nitrites and nitrates. Banned for routine use because of false positives from fertilizers, tobacco, urine and many household nitrogenous compounds.
- Status
- Historical, no longer used routinely
- Reagent
- Diphenylamine in sulphuric acid
- Positive indicator
- Blue colour change
- Reason for discontinuation
- High false-positive rate
Common questions
What replaced the paraffin test in modern gunshot residue analysis?+
Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) replaced it, since it identifies characteristic lead, barium, and antimony particles specifically associated with primer residue rather than any nitrate-containing substance.
Why did the paraffin test produce so many false positives?+
The test detected nitrates and nitrites generically, and many everyday substances a person's hands might contact, including fertilizers, tobacco, urine, and certain cosmetics, also gave a positive blue colour, making the result unreliable as evidence of firearm discharge.
Related terms
- 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...
- GSR
- Gunshot residue. The mix of particles ejected from a firearm on discharge, composed of primer metals (Pb, Ba, Sb), propellant residues (nitrites,...
- 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...
- Primer
- The small explosive cup at the base of a cartridge that ignites the propellant. Conventional primers use lead styphnate, barium nitrate and...
- SEM-EDX
- Scanning electron microscopy with energy-dispersive X-ray spectroscopy. The electron beam excites characteristic X-rays from each element present in the target grain, giving...
- Sintox Primer
- Lead-free, heavy-metal-free primer chemistry developed by RUAG. Uses diazodinitrophenol (DDNP), tetrazenes and potassium nitrate. Modern Sintox GSR particles contain Zn, Ti and...
- 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...