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Table 2 Techniques applied to extract or lift the sample from different areas at the SOC

From: Gunshot residue detection technologies—a review

Method of extraction/lifting Material used Extraction region Merits Demerits
Paraffin method Paraffin, wax Hands 1. Method found to be very effective and easy to perform in less time. 1. The method is bulky and cannot withstand with heavy instrumental method.
2. Another disadvantage is sometime gave false positive test.
Washing method Acid or water (dil. HNO3 and HCl) Hands, nearby materials 1. Advantageous as the quantity of residue came to be high in less time period. 1. Disadvantage of the method is on using acid may cause interference issues while performing detection of the specific inorganic residues.
Tape lift method Adhesive tape, selotape double-sided Hands, clothes, and hairs 1. Most commonly used procedure for collecting inorganic residues from skin, hair, and other mediums also.
2. Another advantage is it is more effective than swabbing and the method is cheap, with good collection efficiency, and thus able to perform well in SEM.
1. Major drawback of the method is when collecting sample from clothes other debris materials or fiber may get lifted.
Swabbing method Cotton ball, filter paper, organic solvent (acetone, ethanol, etc.) Barrel, hands 1. The solvents used give consistent and stable recovery. 1. Major disadvantage is the interference issues since other compounds or materials may also get dissolved in the solvent.
Glue lift method Sticky glues Hands 1. Advantage in using this technique is its less tacky nature than tape lift.
2.Because of less tacky nature it require less dabs on skin surface and thus collect less debris which would be helpful while SEM analysis.
1. Major drawback is its ineffective nature of lifting.
2. The method may not be found effective in analysis of sample on clothes.
Vacuum lift method Filtered trap attached to vacuum Clothes Major advantage of the method is it is helpful in collecting samples from the cloth from the surface as well as depth of the material. Disadvantage is while collecting sample from the depth which became problematic as it increase the difficulty of interpreting sample analysis, as particle from other shooters may be present.