FORENSIC CHEMISTRY LABORATORY MANUAL

by R.Q. Thompson; Oberlin College

ANALYSIS OF HANDWASHINGS FOR GUNSHOT RESIDUE

 

Objective

To identify gunshot residue, if any, by the presence of lead on the hands.

 

Sample

Hand-swabbings:

Have someone fire a handgun at a firing range. Immediately swab each hand with a cotton swab wetted with 0.8 M nitric acid. Swab the thumb web, palm, and back of the hand. Place each swab in a separate plastic bag and seal. Repeat the process for someone who only handled the gun after it was fired.

Alternatively, prepare simulated hand-swabbings by adding lead nitrate solution to cotton swabs wetted with 0.8 M nitric acid. The added lead standard should contain 50 - 100 µg of lead (fired a gun) or 25-50 µg of lead (handled a gun).

 
Reagents

1000 ppm lead solution (as lead nitrate) in 1% (v/v) nitric acid; nitric acid; ammonium dihydrogen phosphate (ultrapure; matrix modifier)

 

Standard Reference Material

500 ppb lead solution (as lead nitrate) in 1% (v/v) nitric acid

 

Method

Electrothermal atomic absorption spectrophotometry

 

Special equipment

Atomic absorption spectrophotometer with graphite furnace atomizer

 

Procedure

For instructor (detailed); For student (brief)

 

Typical results

Atomic absorption calibration curve for lead


Alternate Method

Scanning electron microscopy / X-ray fluorescence (SEM-EDX)

 

Procedure

(planned for next edition)