Forensic chemistry
Forensic chemistry is a specialized branch of chemistry that applies scientific techniques to analyze nonbiological materials, primarily collected from crime scenes, to assist in legal investigations. It plays a crucial role in the justice system by providing evidence that can be used in court. Forensic chemists often work in laboratories associated with law enforcement agencies, medical examiners, or organizations like the Federal Bureau of Investigation (FBI). Their work encompasses various areas, including toxicology, serology, and arson evidence analysis, employing advanced instruments like gas chromatographs and mass spectrometers to identify and separate chemical substances.
The field has evolved significantly since its early days, with notable advancements made in the 19th century, leading to more systematic and regulated approaches in the 20th century. Modern forensic chemistry utilizes sophisticated analytical methods to re-examine evidence from past cases, often providing insights that were previously unattainable. Common applications include drug identification, breath alcohol testing, and analyzing latent fingerprints using chemical reagents. Forensic chemists must interpret complex data and may be called upon to present their findings in legal proceedings, making their expertise vital in the pursuit of justice.
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Forensic chemistry
Forensic chemistry is chemistry applied to legal questions to analyze nonbiological material. This material is usually collected at crime scenes and may be used as evidence in court. The word forensic refers to the application of scientific methods and techniques to crime investigation.
Most forensic chemists work in laboratories affiliated with police departments, medical examiner's offices, or agencies such as the Federal Bureau of Investigation (FBI). They study analytical, general, and organic chemistry, and may specialize in other areas of expertise, such as microchemistry.
Little evidence of forensic analysis exists before the nineteenth century, although ancient scholars were aware of chemistry. In modern times, numerous scientific advances have been applied to forensic chemistry. In fact, new advances have allowed law enforcement to reexamine evidence from old investigations and in many cases find answers that were not possible a few decades earlier.
Background
Some of the earliest studies of chemistry date to ancient Egypt, Greece, and Rome and primarily focused on poisons. Poisons were commonly used as murder weapons and to execute people. Crime investigators relied on circumstantial evidence and hearsay, or what people had heard about crimes. Arsenic was commonly used for centuries as a murder weapon. In the eighteenth century, chemists developed the first tests to detect the poison. Scottish chemist James Marsh developed a test that accurately detected arsenic in a body in 1836. The test was soon put to use in a murder trial.
Forensic science was not regulated and was largely self-taught until the twentieth century. The first forensic science program was established in Switzerland in 1902, and the first police science programs in the United States began during the 1930s. The American Academy of Forensic Science was formed in the 1950s.
Many tools important in forensic chemistry, including the gas chromatograph and mass spectrometer, were developed during the twentieth century. With new technology and techniques, crime-scene processing became increasingly important moving into the twenty-first century. Law enforcement agencies established procedures to ensure crime scenes were not contaminated and evidence was properly preserved. A plethora of crime-scene-investigation television dramas drew audiences into the forensic sciences.
Overview
Forensic chemists may apply many types of analysis, such as arson evidence, serology (study of body fluids and serums), or toxicology (analysis of toxins and toxicants). They must become skilled in the use of laboratory instruments and techniques, such as gas chromatography, mass spectrometry, and neutron activation analysis. Evidence collected at a crime scene may contain multiple materials, which require chemists to identify and separate components using appropriate techniques.
The gas chromatograph (GC) is one commonly used instrument. It can be used to separate a substance such as a drug from other substances, such as mixing agents or materials from the environment. To analyze a substance, the chemist injects it into the GC. Molecules have varying density, so they move through the GC column at different speeds. Heavier molecules move more slowly, for example. A GC is usually used with a mass spectrometer, in which the molecules pass through an electron beam that causes the substance to break apart. Scientists examine how the substance breaks apart to determine its identity. These tests can be used in many types of cases, such as hit-and-run investigations, when investigators need to identify or compare paint samples; in arson investigations, when scientists must determine if flammable materials were used to start a fire; and in crimes when investigators need to check suspects, victims, and weapons for gunshot residue. Mass spectrometry (MS) is also used with other equipment, such as high-performance liquid chromatography (HPLC), which is often used to discern the presence of various drugs.
Criminal investigations often involve controlled substances. Before suspected drugs can be used as evidence of a crime, they must be properly identified. Forensic chemists may use a variety of methods to identify substances. First, investigators use presumptive tests, such as field color tests. For example, the Marquis color test uses formaldehyde and concentrated sulfuric acid, which will turn purple in the presence of heroin, morphine, and most opium-based drugs, or orange-brown in the presence of amphetamines. Other color tests include cobalt thiocyanate, distilled water, glycerin, hydrochloric acid, and chloroform, which will turn blue in the presence of cocaine, and cobalt acetate and isopropylamine, which will turn violet-blue in the presence of barbiturates. Forensic chemists next use confirmatory tests to narrow down the identity of the substances. For example, ultraviolet spectrophotometry analyzes how a substance reacts to ultraviolet (UV) and infrared (IR) light. The microcrystalline test involves adding a chemical on a slide to the suspected substance and examining the resulting crystals under a polarized light microscope. Each type of drug will form a distinctive chemical pattern. After testing, the scientists interpret the data to reach a conclusion about the substances. This may involve identifying both controlled substances and other particulates in the sample. Forensic scientists document the results in reports and may be called to offer expert testimony about their findings in legal proceedings.
Breath tests to check for intoxication are also examples of forensic chemistry processes. The field test devices, called Breathalyzer kits, are used to estimate blood alcohol content by analyzing the ethanol levels in an individual's breath. Law enforcement may use a variety of methods, including portable infrared spectrophotometers, fuel cells, or chemical reagents. The latter is the most commonly used. When the individual blows through a tube, the breath bubbles through a chemical solution of sulfuric acid, potassium dichromate, water, and silver nitrate. Alcohol oxidation causes a reduction of dichromate ion to chromic ion, and the color changes from orange to green. A photocell device compares the color change to determine the alcohol content.
Chemistry may also be employed to find evidence at a crime scene. For example, technicians may use gaseous fumes to find invisible, or latent, fingerprints. Commonly used chemical reagents include cyanoacrylate (instant glue or Super Glue), silver nitrate, iodine, and ninhydrin. Cyanoacrylate fumes react to amino acids in fingerprint residue and turn the prints white. This process may be done in a lab in a fuming chamber or at a crime scene using a handheld wand-shaped tool. Silver nitrate fumes react to chloride in the fingerprint residue, forming silver chloride, which can be seen under ultraviolet light. Iodine fumes react with oils in prints, turning the prints brown. The prints will fade in minutes unless sprayed with a fixing solution. Ninhydrin is applied in a spray solution and reacts very slowly to oils in latent prints. The process can be speeded up by applying heat. Any fingerprints turn blue or purple.
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