Table 1 Traditional color based preliminary tests used for the presence of GSR
From: A chronological study of gunshot residue (GSR) detection techniques: a narrative review
Sl No. | Color test | Reagents and materials used | Analytes | Color changes observed | Demerits | Literature |
|---|---|---|---|---|---|---|
1. | Dermal nitrate/paraffin test | Diphenylamine dissolved in strong H2SO4 | Nitrates | Deep blue coloration | It showed positive results for those who were in contact with nitrates or nitrites from other sources like fertilizers, waste water, sewage lines, acid rain etc. | Edwin et al., (Conrad, 1961) and Tagliaro et al., (Tagliaro et al., 2002) |
2. | Marshall and Tiwari Test | Desensitized photographic paper Sulphanilic acid N-α naphthyl-ethylenediamine hydrochloride in methanol Acetic acid | Nitrites | Purple color spot | lt destroy the sample and show interference with other environmental constituents The test is specific for nitrites and not for GSR | Shrivastava et al., (Shrivastava et al., 2021) |
3. | Griess test/Walkers test | Bromide paper treated with 2-napthylamine disulphonic acid CH3COOH | Nitrites | Dark red color | many compounds other than nitrocellulose propellants can give positive reaction eg. Urine | Shrivastava et al., (Shrivastava et al., 2021) |
4. | Modified Griess Test | Reagents used for Griess test + 2 naphthyl amine sulphanilic and citric acid | Nitrites | Pink color | It can be applied to detect nitrites only but not for GSR. | Jaluddin et al., (Jaluddin et al., 2021) |
5. | Harrison and Gilroys test | Swab moistened with dil. HCl tri-phenylarsonium iodide and sodium rhodizonate | Antimony Lead & barium Lead Barium | Orange Red Purple No change in color | Interference with other materials at the crime scene can be obtained. | Sharma., (Sharma, 1978) |
6. | Di-thio-oxamide test | Di-thio-oxamide (DTO) in ethanol Ammonium hydroxide dissolved in distilled water filter paper | Copper Nickel | Gray/greenish blue or violet color | Is in presence of blood false negative result can be obtained | W. Arendse (Arendse, 2008) |
7. | Sodium rhodizonate test | HCl Sodium rhodizonate | Lead (When pH is neutral) Lead (when pH below 3) Barium (at any pH) | Varies from blue to violet. Bright red color with orange tint Reddish brown | It cannot be applied for Ba detection | Jefffrey S Taylor (Taylor, 2017) |