One of the fundamental principles that govern specifically Forensic Science and Forensic Chemistry based on the premise that when two objects come into contact, there will be an exchange between the two. Ie
"every contact leaves a trace" , A phrase popularized
Edmund Locard, the father of modern criminology, causing a shift in research methodology. That is why the forensic chemical traces this exchange between material and brings to light what is invisible to the eye. Based on your knowledge and technologies developed, has the ability to track substances or marks they left on a crime scene.
forensic chemist, so working with non-biological substances such as paint, glass or liquid, traces of gunpowder from a shot, all samples can be well analyzed using appropriate analytical methods.
Another field in which a forensic chemist can develop it in Toxicology which mainly deals with biological samples, urine, hair, blood, semen, saliva or gastric contents and thus to determine for example the level of alcohol or drugs that a person consumed. Understand
evidence requires tools from many disciplines such as Analytical Chemistry, Biology, Materials Science and Genetics. In fact, DNA analysis is making knowledge in genetics is very important.
Over time analytical chemistry has become an important research criminal, especially when it comes to knowing the intrinsic nature of any substance or component and moreover, when used to aid in scientific investigation of crime.
Therefore forensic chemists have three main tasks: first, analyze the evidence in the laboratory then interprets the information out of them and finally, you can get to defend what was found by the witness of forensic chemist at trial. Applications
Forensic Chemistry is applied in a variety of techniques, both qualitative and quantitative, whose main purpose is to search responses from the different evidence that may contribute to the resolution of any criminal case.
Some of these tests are as follows:
- Drug Test is currently looking for the presence or absence of drugs, either in powders, liquids, tablets or capsules. Laboratory are qualitative tests that are done by attaching an antigen and its homologous antibody, to identify and qualify specific antigen and antibody in a sample; to them are called immunoassays. The method involves using a mixture of
antibodies selective for different drugs (active) and its metabolites, obtaining a result with a high degree of sensitivity.
- Analysis of samples of fire The manner in which a fire occurs naturally in a room indicates whether the beginning was deliberate or not, but the evidence is hard to find in such cases because it is often covered by debris.
fires are usually caused by the use of combustion accelerators, which are examined by gas chromatography coupled to mass spectrometry, which can identify those ignition liquid waste present in the samples of debris. The forensic chemist should concentrate small amount of sample by adsorption accelerant residue in strips of charcoal. This concentrate is then eluted from the activated carbon dissolving in a suitable solvent, leaving the sample in an appropriate manner and then analyzing by chromatography.
- Analysis of footprints physicochemical tests used in the case of studying the footprints left at a crime scene and then compared with those obtained from a suspect's shoes. Through an electrostatic process, the final sample is obtained on a gelatinous matrix which contains a layer of adhesive that can lift fingerprints of almost the majority of surfaces, including porous materials or coal. This procedure can also be used when the tread can not be seen (eg if the suspect is standing on a sheet of newspaper), as the dust from the sheet of newspaper printing will show the unique tread, or even the brand of shoes that the individual used.
- Analysis of traces of paint. The trace of paint left in a car accident where the offender fled in his vehicle, used to relate it to the suspect vehicle. In this way you can get data on manufacturing and vehicle year in which it was made. This type of testing can be performed by observing the absorption spectrum of the sample composition painting or watching a
Fluorometer
- Use safe water (nitric acid-water). Each gun is engraved with a unique serial number, which in some cases criminals are removed or sanded to prevent tracking and identifying the weapon as part manufacturer. Using the chemical restoration, in this case the use of etching, the numbers may again be readable again.
- Analysis of gunshot residue and bullet Waste of the discharge of firearms is another area of \u200b\u200bresearch. These residues can be found on the hands or clothing of a suspect. Forensic chemists may find the classification of the weapon and related to the type of bullet found at a crime scene. When a gun is fired, gases are generated containing burned and unburned components from the caps of the bullet and gun propellant. This material can be deposited in the victim's clothing or hands of the person who fired the gun, becoming waste. Using a scanning electron microscope coupled with an energy dispersive spectrometer, the samples can be examined possible breakage collected from suspects. This instrument is capable of searching hundreds of sites the tiniest microscopic particles of residue.
- Falsification of documents. Using electrostatic detection apparatus can identify the different grooves of the writing in the case of forged signatures or alteration of documents. In this case applying an electrostatic discharge on the surface of the paper, cause different patterns in places where the cracks are caused by writing. By applying an opposite charge, a black ink stick in the places of the recesses.
- Qualitative analysis in case of poisoning. In this case, determines the individual molecule is present in the sample. Over time it has been able to collect much information about these substances, their composition, what type of drugs are so. This type of test is usually performed by photometry, although there are specific chemical test for some substances. When it comes to natural poisonous substances are more difficult to identify. Even if the species is correctly identified, there are variations in the amount of active substance present, so that should carry out studies on the molecular composition and thus confirm the presence of harmful substances.
- Search fingerprints. The most popular technique used to reveal fingerprints is using activated carbon powder finely sifted. Most people's fingers are greasy and oily composition. When they come into contact with any surface or relatively soft material, friction oils released from the grooves of the tread. When the powder is applied to the surface, it sticks to the oils and reveals the pattern of the fingerprint. This technique is widely used in samples of wool, metal, glass or plastic. In the case of the fingerprint on a surface is very colorful fluorescent powder is used. When the surface is exposed to ultraviolet light, the glow powder showing the fingerprint, no matter what background color you are. In porous materials such as leather, wood or paper surfaces, the preferred technique is the use of magnetic powder, consisting of finely divided iron particles which are suspended on the surface using a magnetic bar.
- Detection of blood spots. 
All tests used in blood testing are mainly based on the activity of peroxidase enzymes in the blood, which react to chemical agents causing a color change. Some of the tests used are the benzidine test, leucomalachite green, phenolphthalein or tetramethyl benzidine. But one famous Losman is the use of Luminol, used in forensic chemistry to detect traces of blood. This compound is a derivative of phthalic acid which catalyzes the oxidation with hydrogen peroxide on light emission, that is its greatest importance lies in the chemiluminescent reaction that occurs with peroxide in the presence of iron complexes as catalysts.
- Analysis of biological samples (urine, blood or stomach contents) and hair. The biological samples used provide information about the presence of a toxin in particular, or its metabolites in the body. It must take into account the average life time of toxins, the volume of distribution and affinity for different tissues. The main signs in this type of analysis, are blood, plasma or serum, as these substances distributed throughout the body. In cases of poisoning or death by poisoning, are chosen as samples of gastric contents that may contain traces of tablets or liquids that can guide research. In organs like the kidney and liver and bile, from the autopsies, can be found high concentrations of toxic substances. Also in brain tissue, which provides information on the detection of psychoactive substances acting on central nervous system. For the case in the investigation of the recent use of drugs in living individuals, the urine samples are important because it is excreted by active and / or its metabolites of the toxic substance. Chronic use, however, is mainly analyzed in hair samples because they provide a kind of "schedule of consumption" due to the toxic substance is not metabolized in the hair.
- Role of Analytical Techniques. is important to emphasize the role essential that meets the analytical instruments in the above techniques, and thanks to advances made by forensic scientists instrumental is possible to reach accurate results, so necessary in defending the methodologies and results obtained before the law. It is therefore increasingly important to have more sensitive instruments capable of reaching detection limits smaller by using minimal amounts of sample and analytical techniques coupled, in order to determine the presence of substances which in the recent past it was believed did not exist.
Today, the development of instrumental analytical is strongly oriented to the field research, where scientists have turned to the introduction of "mobile laboratories", characterized by the use of laptop computers useful when working with volatile substances, perishable or too toxic to carry the laboratory. An example of this type of equipment is portable Gas Chromatograph coupled with Mass Spectrometer (GC-MS), which has reduced the size of conventional equipment of 114 kg to a 28 kg.
Without the necessary chemical basis, many of these techniques could not be applied to forensic science, therefore it is important that the development of analytical chemistry to move forward and contributing to the criminal investigation.
In Chile, the introduction of the new Criminal Procedure Reform justice system, requires the formation of a forensic science or forensic institutions capable of rapid responses in the interpretation of the evidence, able to create new analytical techniques to our national reality and, above all, capable of generating one hundred percent dedicated professionals to the science of criminal investigation.
While Forensic Science and Forensic Chemistry especially here in Chile is still a nascent science delivered mainly police institutions and the Legal Medical Service, it is possible to envision a future auspicious forensic research universities, opening the way to new researchers eager to push the boundaries of chemistry into a science that is fundamental pillar of criminology and very important link at the administration of justice and seek truth. References
. "Manual of Forensic Chemistry." Patricia M. Caro. Editions of the Rock. Buenos Aires, Argentina.
2004. Web Lawrence Livermore National Laboratory, Forensic Science Center. San Francisco, USA . Handbook of Forensic Services 2003. Manual FBI Forensic Laboratory.
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