A review of
“Unambiguous Characterization of Gunshot Residue Particles Using Scanning
Laser Ablation and Inductively Coupled Plasma-Mass Spectrometry”
Unambiguous Characterization of Gunshot Residue Particles Using Scanning Laser Ablation and
Inductively Coupled Plasma-Mass Spectrometry, Abrego, Z., Ugarte, A., Unceta, N.,
Fernández-Isla, A., Goicolea, A., Barrio, R., Analytical Chemistry., 2012, 84(5), 24022409
Olivia Yaple April 14, 2012
Through the use of Inductively Coupled Plasma Mass Spec and Scanning Laser Ablation
in this experiment researchers were able to come up with a new method for detecting and
identifying gunshot residue from firearms. This new information will help with investigation
process when firearms are involved. Up till now the best way to detect gunshot residue is to look
at the elements that were discharged during the shot. Researchers say that this type of GSR
detection should be the main type because most of the time what you find depends on the
conditions when the firearm was shot and the distance from point of production to impact can
vary greatly. There are also several other factors that can result in alternative outcomes including
the type and age of gun, the suspects hygiene and occupation, and how long the investigation
took place after the incident.
Over the years there have been several kinds of methods that have been used for the
detection of GSR. Some of them worked and others were not as reliable. SEM, AA, and ICP-MS
are among the few that did produce results in the identification of metals from GSR; however
they were not able to classify the elemental composition of individual particles because these
methods were more bulk analysis and were only able to see the elements involved. Using ICPMS and Laser Ablation (LA), there’s no need for ample sample preparation and the laser directly
focuses on the sample surface and converts the solid sample to a vaporized form which are then
transformed to the ICP. The standard carrier gas for the experiment was Helium and Argon
nebulizers were used to as well to turn the sample into an aerosol before being introduced to the
plasma. There were 17 isotopes of the 15 elements that were analyzed including Al, P, S, Cu, and
Pb, because these are the elements most likely to be found in gunshot residue and are what
characterize samples and particles as GSR. These elements came from various parts of the
firearm including the cartridge case, primer, the bullet, and the barrel of the gun.
There were four different firearms used for this test. They were a 9mm pistol, 38mm
revolver, 22mm revolver, and a 45 auto pistol. Most of these firearms are commonly used on the
police force or were used in crimes in the region. The firearms were shot in a shooting range at
the laboratory in Spain and there was no specific technique for firing and an unlimited amount of
shots fired. Before beginning each one was cleaned to reduce the risk of contamination from
previous use. The researchers used carbon-adhesive tape to life any or all gunshot residue from
the shooters hands and all samples were collected within 5 minutes of the initial shooting. For
analysis the ICP and LA were optimized to improve the sensitivity, reduce the number of doubly
charged ions and minimize fractionation effects. In order to identify what makes up for GSR
particles, there must be the detection of signals corresponding to Pb, Sb, Ba isotopes, which are
the main components of GSR.
When using the LA, Pb, Sb, and Ba were all identified at the same ablation time gave the
researchers significant results showing that their subjects were positive for GSR. The study also
found that the pistols give off a greater amount of GSR than the revolvers as well as more GSR
on the back of the hand than their palms because the palm of the hand is in direct contact with
the arm of the gun and only receives a small amount of GSR. If the shooters were not wearing
gloves there is the possibility of skin cells being lifted during the tape process and through the
use of the LA, it destroys any skin cells that would have appeared in the images and take out any
interference that may results from the skin cells being there. The ICP-MS and LA methods
proved to be better than what was previously used with faster times and better results. They were
able to eliminate any outside interferences including skin cells and other matter that may have
gotten caught in the adhesive tape lift of GSR residue.