How does forensics relate to chemistry

Personal Characteristics Versatility and patience are the most often cited qualities of a forensic chemist.

Forensic chemists must be able to spend hours rigorously applying analytical techniques to evidence and defending their work in a court of law. They must be able to clearly and concisely answer challenges to their findings. Education and training A strong background in chemistry and instrumental analysis as well as a good grounding in criminalistics is vital. A forensic science degree at both the undergraduate and graduate level is recommended.

Those interested in working with trace evidence, such as glass, hair, and paper, should focus on instrumentation skills and take courses in geology, soil chemistry, and materials science. If forensic biology and DNA analysis are preferred, take microbiology, genetics, and biochemistry courses. Those interested in the toxicology aspects of this work should study physiology, biochemistry, and chemistry. Job Outlook The forensic chemistry field is guardedly optimistic about job prospects for the future.

Greater interest in the use of DNA analysis is expected to create jobs. Those interested in DNA work should keep up with the rapidly changing technology and develop skills that distinguish them from the pack.

Neutron activation analysis of hair from the body showed that hair that was several centimeters long contained little arsenic, but that shorter hair closer to the scalp which had grown in the few days before death contained high levels of arsenic, indicating that death was probably caused by arsenic poisoning. Often, the presence of very small impurities makes comparison possible. For example, cars are painted with paints prepared to certain specifications of color and composition, and pigments and binders used vary from one manufacturer to another and even between models from the same distributor.

A small sample of paint left at the scene of an accident may be checked for color by spectrophotometry and then analyzed for composition. Residues left by burning powder from firearms consist of patterns of particles that have both characteristic physical and chemical properties. Burned powder, for example, usually contains traces of nitrites that yield chemical reactions and traces of metals such as barium that are often present in primers.

Both chemical reactions and microscopic analysis including electron microscopy are employed in the identification of powder residues on clothes and skin. An early method for detecting gunshot residue on the hands of suspects involved coating the hand with melted paraffin , allowing the paraffin to cool, and then stripping it off. Gunshot residues transferred from skin to paraffin turned blue or green in the presence of diphenylamine, but many common substances such as urine gave a false positive test.

The Greiss reagent is much more definitive, and additional tests can identify traces of lead around bullet holes. Even microscopic particles are found to have definite compositions and can be unequivocally identified. Toxicologists examine a wide range of materials such as blood stains, urine, and blood gases for traces of poisons or drugs.

Many businesses now require the drug screening of employees; it is the responsibility of the technician to distinguish between the presence of illegal drugs and metabolites from foods such as poppy seeds. Such tests may be as simple as paper or thin-layer chromatography or as complicated as gas chromatographic or electrophoretic and serological analysis of a blood sample. Following death by unknown cause, samples of the victim's lungs, blood, urine, vitreous humor, and stomach contents are examined for traces of poisons or medication.

Insects found on or near corpses are also collected and examined; they may actually absorb traces of drugs or poisons from the body, and in fact, traces of poisons sometimes are found in the surrounding insects long after concentrations in the body have fallen below detectable limits.

Forensic biochemists perform blood typing and enzyme tests on body fluids in cases involving assault, and also in paternity cases. Even tiny samples of blood, saliva, or semen may be separated by electrophoresis and subjected to enzymatic analysis. In the case of rape, traces of semen found on clothing or on the person become important evidence; the composition of semen varies from person to person. Some individuals excrete enzymes such as acid phosphatase and other proteins that are seldom found outside seminal fluid, and these chemical substances are characteristic of their semen samples.

The presence of semen may be shown by the microscopic analysis for the presence of spermatozoa or by a positive test for prostate specific antigen.

In cases of sexual assault, tiny samples of DNA in blood, semen, skin, or hair found on the victim may be purified and the amount of DNA increased by the use of a polymerase chain reaction to produce quantities large enough to analyze. Since DNA is as specific to a person as fingerprints, matching the DNA of a perpetrator to a sample found on a victim is considered to be proof of contact.

Many perpetrators of crimes have been convicted and many innocent persons set free after years in prison as a result of DNA analysis. Accidents caused by intoxicated drivers kill nearly 15, persons a year in the United States alone almost half of fatal auto accidents are alcohol-related , so a Breathalyzer kit is standard equipment in most police squad cars or state patrol vehicles. Breathalyzers are used to estimate the blood alcohol content of drivers suspected of being intoxicated; the driver may appear sober, but still have a blood alcohol level above the legal limit.

Although it is impractical to take blood samples on the highway, research has shown that the concentration of ethanol in the breath bears a definite relationship to its concentration in blood. Many communities have now set a legal limit of 0. In fact, authorities now consider that a person's driving ability is probably impaired at a blood ethanol level of 0.

Several types of analytic devices are available to administer Breathalyzer tests. One test makes use of a portable infrared spectrophotometer, another uses a fuel cell, and the most common test employs several glass or plastic tubes and some common chemical reagents.

The person being tested blows through a tube, which bubbles the breath through a solution of chemicals containing sulfuric acid, potassium dichromate, water, and silver nitrate.

Oxidation of the alcohol results in the reduction of dichromate ion to chromic ion, with a corresponding change in color from orange to green. An electrical device employing a photocell compares the color of the test solution with a standard solution, giving a quantitative determination of the alcohol content. The test provides a quick and reproducible determination of the amount of alcohol in a person's breath and is a numerical measure of the amount of alcohol in the bloodstream. Use of a chemical test helps to avoid subjective opinions of sobriety and provides reliable evidence for court proceedings.

The test can be readily and quickly administered by trained law enforcement personnel, but forensic chemists test and calibrate the equipment and testify to its accuracy. Fingerprints on smooth surfaces can often be made visible by the application of light or dark powder, but fingerprints on checks or other documents are often occult hidden.

Occult fingerprints are sometimes made visible by the use of ninhydrin, which turns purple due to reaction with amino acids present in perspiration. Mass Spectrometry MS breaks samples apart and separates the ionized fragments by mass and charge. Generally, forensic chemists are trained in organic chemistry.

This ensures that the forensic chemists can run analysis on blood and other body samples to identify DNA. They are also trained in organic chemistry so that they can run toxicology screenings. It is also important for a forensic chemist to have knowledge of physics. There are also forensic chemists who specialize in certain areas, such as chemicals that are tied to explosives or arson. These chemists will be called to a crime scene to look at fire patterns when determining if arson was involved in a fire or they will be called to investigate chemicals associated with a bomb.