The trace metal detection test or technique was developed during the Vietnam War in the 1960s to identify individuals who may have been carrying firearms against their skin. A 0.2% solution of 8-hydroxyquinoline in isopropanol is sprayed on the skin. After several minutes, the skin is illuminated with shortwave ultraviolet (UV) light, revealing a pattern and type of metal based on trace amounts of metal transferred to the skin, which are invisible under normal lighting.[1] The technique was later adopted by police in the United States to help determine if a person had carried a firearm. In a California crime, an automatic handgun carried in the waistband of a criminal reportedly produced an impression of the weapon's serial number.[2] The presence and persistence of a detectable residue depend primarily on the amount of perspiration, length of contact, and time since exposure. A few minutes of exposure can leave detectable residue, and the result can remain for up to forty-eight hours.[3]
Preservation of the results is achieved with black-and-white and color photography. The use of a shortwave ultraviolet filter over the camera flash can be employed to record the results, although a steady source of UV is preferred.[4] In either case, a darkened area is needed for screening purposes. Another reagent, 0.5 percent 2-nitroso-1-naphthol in acetone, eliminates the need for a UV light but is limited to a four-hour window compared to the forty-eight hours for 8-hydroxyquinoline.[5]
References
edit- ^ Ultraviolet Detection of Metal Traces - Trace Metal Detection Technique - Final Report; J.O.Rhoads; Minnesota Dept of Public Safety State Highway Patrol; 1971; http://www.ncjrs.gov/app/publications/abstract.aspx?ID=34019
- ^ Honolulu CSI: An Introduction to Forensic Science and Criminal Investigation; p. 39; Gary A. Dias and Robbie Dingeman, cy 2004, Bess Press, Inc.
- ^ "Gunshot Injuries" by Vincent J.M. DiMaio from the Elsevier Series in Practical Aspects of Criminal and Forensic Investigations, Elsevier Publishing Company (October 1989); pp 267-283.
- ^ Trace Metal Detection Technique (TMDT) - A Report Outlining a Procedure for Photographing Results in Color, and Some Factors Influencing the Results in Controlled Laboratory Tests; J.M.Stevens; H.Messler; Journal of Forensic Sciences; Volume:19 Issue: 3: JULY 1974; Pages:496-503
- ^ Study of the Use of 2-Nitroso-1-Naphthol as a Trace Metal Detection Reagent, C W Kokocinski; D J Brundage; J D Nicol; 1980; http://www.ncjrs.gov/app/publications/abstract.aspx?ID=73257