Local law enforcement

The analysis of gunpowder using atomic absorption and inductively coupled plasma is another technique used by forensics to help solve cold cases. Combustion of the primer and powder of the cartridge is caused by firing a weapon. Unburned primer of powder components, or the residue of the combustion products, can be used to detect a fired cartridge. Residue can be found on the skin or clothing of a person who fired a gun. It can also be found on an entrance wound of a victim, or even on the target materials at the scene.

The discharge of a firearm, particularly a revolver, can deposit reside even to an individual that is close to a person who fired the gun (Thomton, 1986). Lead (Pb), barium (Ba), or antimony (Sb) was the major primer elements. A smaller amount of elements contain aluminium (Ai), sulphur (S), Calcium (Ca), tin (Sn), Chlorine (Cl), silicon (Si), or Potassium (K). This element varies depending on who and where the ammunition is manufactured.

A mercury-fulminates based primer may be found in ammunition manufactured in Eastern Europe and Used in the Middle East (Zeichner, et al, 1992) Primer elements may be easier to detect in residues because they do not get as hot as the powder, and compounds may be detectable. (Tassa et al, 1982). Current gunpowder, or the so-called “Smokeless” powder, can contain up to 23 organic compounds (FBI). On the other hand, samples must be extracted from the skin surfaces of a victim at the scene. Samples must be obtained immediately, washing of the body prior to autopsy or even movement will diminish or destroy gunshot residues (Kitty, 1975).

Atomic absorption spectroscopy or was applied determining the amount of copper, zinc and nickel in entrance skin wounds and cloth injuries made by different type of jacketed bullets. This method measures trace element signatures, but it is the oldest techniques used in forensic today. In order to analyze a combination of elements, such as those found in gunshot residues, a solution of the mixture is vaporized by a flame, through which is shone light thought to be characteristic of an element in the mixture. If there are any of these elements present, it will absorb the light, leaving dark lines in the absorption spectrum.

One of the key methods for detecting primer residues is Atomic Absorption (AA) or atomic absorption spectroscopy (AAS). By definition, atomic absorption (AA) is an analytical technique, used to determine the elemental composition and concentration of many metals and other inorganic elements. The material being analyzed, generally in solution, is atomized, or broken up into individual atoms, usually by the action of extreme heat in a flame or small furnace. The ability of the atomized material to absorb characteristic wavelengths of visible or ultraviolet light is then measured using a spectrophotometer.

Inductively Coupled Plasma Spectrometry or ICP replaced the atomic absorption method. However, due to the fact that AA or AAS is relatively simple and low cost, has guaranteed a place in laboratory bench for the predictable future. ICP is an analytical technique used for the detection of trace metal in environmental samples. The primary goal is to get elements to emit characteristic wavelength specific light, which can then be measured. This technology method was first employed in the early 1960’s, it is intended in improving crystal growing techniques.

Since then, ICP has been refined and used in conjunction with other procedures for quantitative analysis. Today inductively coupled plasma is used in forensic by means of combining ICP with Atomic Emission Spectroscopy. This is advantageous over the other method mentioned above, since AES require that sample to be in a gaseous form proceeding to injection into the instrument. Thus, using ICP in combination with these instruments eliminates any sample preparation time, which would be required in the absence of an ICP.

Advantages of using an ICP include its ability to identify and quantify all elements with the exception of Argon (Traci Bradford, 1997); since many wavelengths of diverse sensitivity are available for determination of any one element, the ICP is appropriate for all concentrations from ultra trace levels to major components; recognition limits are normally low for most elements with a typical range of 1 - 100 g / L. most likely the largest advantage of employing an ICP when performing quantitative analysis is the fact that multi-elemental analysis can be achieved, and quite rapidly.

A whole multi-element analysis can be accomplished with in 30 seconds, consuming only 0. 5 ml of sample solution. It is much obvious that this is a better method than the other. ICP methodology coupled with Atomic Emission Spectroscopy is now commonly used in forensic science. One possible usage of the said method is the determination of toxic metal ions in beverages. If the toxic ions are mixed with the beverage in a criminal case, it is required to make precise determination and detection of these ions.

Since ICP-AES is a proven practice to detect these toxic ions such as Cu, Cd, Tl and Pb it will be advantageous to use this methods than Atomic Absorption analysis.

References

Boumans, P. W. J. M. Inductively coupled plasma-emission spectroscopy. New York: John Wiley & Sons. Jackson, B. , Willian, S. , Davis, L. (2001). Federal support of state and local law enforcement. Santa Monica, CA. Rand. Watts, S. , Haliwell, L. (1996). Essential environmental science: Methods and techniques. New York. Routledge. Zonderman, J. (1999). The new science of investigation. New York. John Wiley & SonsW