First when identifying drugs the chemist should conduct screening tests to reduce and limit the possibilities. The screening test should have some kind of eliminating process that allows the chemist to test the attributes that identify the substance whether drug or other type of substance. This is usually called the first stage of testing the plain should be outlined and documented part by part until a conclusion is made that reduces the possibilities of substances that the test items are. Preliminary tests should be conducted in the laboratory until a main substance is identified then a confirmation test should be used to confirm that the test yields the correct drug item and chemical solution.
Even if the Police tell the Chemist what items they are searching for many tests should be performed to identify what type of substance was sent to the laboratory. Another issue is how much of the substance you have to sample from this could change your testing procedures if you have less of the sample then the first testing procedure must be more precise to identify the substance.
The first steps to identifying drugs are to use a number of color tests. Color test involve deferent chemicals that make the substance change color that allows the Chemist to identify what the substance is if it is a drug or another substance. The five main Chemical tests are the Marquis, Dillie-KKoppanyi, Duquenois-Levine, Van Urk, and the Scott Test.
The Marquis test uses 2 percent formaldehyde in sulphuric acid if the substance turns purple then heroin, morphine or opium is present in the tested substance. If the color of your slid turns orange brown then amphetamines or methamphetamines are present.
The Dillie-Koppanyi test uses 1 percent cobalt acetate placed inside of methanol then 5 percent isopropylamine. If the color of the substance slid turns violet-blue then the slide contains barbiturates.
The Duquenois-Levine test is divided into three different solution A, B and C. Solution A consists of 2 percent acetaldehyde in ethyl alcohol. Solution B consists of hydrochloric acid and solution C consists of chloroform if the color of the test turns purple then you have marijuana.
The Van Urk test uses 1 percent solution of p-dimethylaminobenzaldehyde mixed with 10 percent hydrochloric acid plus ethyl if the test color turns blue-purple then your substance is LSD.
Scott Test consists three different solutions A, B, and C Solution A consists of 2 percent cobalt thiocyanate dissolved in water and glycerine, solution B is Concentrated hydrochloric acid and solution C is chloroform. If the color solution turns blue when tested with solution A then clear pink when added to solution B and then if it turns back to blue when added solution C you have a positive test for cocaine.
The Microcrystalline test is a more specified test than using Color tests it uses a chemical regent that is placed on a microscope slide the chemical reaction produces crystals that can examined by a microscope the shapes of the crystals formed can properly identify any substance that may be a drug.
Gas Chromatography or GC identifies illicit substances by using stationary liquid to produce gas that rises into the surrounding environment. The sample is injected into a heated chamber, a constant stream of nitrogen gas flows through the injector forcing the sample through a series of seven columns that has a thin film of liquid present. The columns separate the gases and then the gases enter the detector that activates the recorder producing a recording that traces peaks and valleys based on a timed scale that identifies the concentration of drugs.
Paint evidence from an automobile accident can lead you as a detective to identify the make and model of a vehicle by the body paint. The fact that motor vehicle corporations apply more than one coat of paint on vehicles that are sold in the United State the investigator has four distinctive types of paint on the automobile to analyze.
The first paint coat is the Electrocoat primer it is generally the first coat of paint applied to the cars steel it consists of a epoxy-based resin that is electroplated to the vehicle body steel.
The primer surface keeps the vehicle from rusting and other corrosions. It is made of epoxy polyesters or urethanes this layer of paint smoothes the crack and crevices to allow the base coat not to show any seams.
The base coat of paint or color coat is the coat that gives the vehicle its color. It keeps UV light from damaging the color of the vehicle it is made of acrylic based polymer.
The Clear coat is made to improve glossy finish they are acrylic based and protect the paint from losing contrast and color.
Pyrolysis Gas Chromatography has been proven to find the elements that are located inside of different types of paint. The Pyrolysis Gas Chromatography separates the composition of paints by heating the filaments until they decompose then sending the separated chemicals throw a detector.
When collecting and preserving paint evidence the investigator must look for paint evidence on the crime scene. Paint evidence can be found on the ground on a person from a hit and run or on adjacent vehicles that may have been hit or damaged. The paint chips should be collected with a pair of tweezers or a piece of clean white paper this is to keep the paint chips from being contaminated. The paint chip should be stored inside glass or plastic valves if found inside clothes or on objects then place the item inside of a paper bag or a box and send it into the lab whole. Use a clean scalpel to gather paint evidence for comparison from undamaged area and label. Gather paint samples from damaged area and label for comparison with paint found in clothes or on objects. Make sure to clean your scalpel or use a new scalpel for each sample this way you will not contaminate the paint evidence.
When collecting fire evidence make sure to package all evidence properly in sealable paint cans and label all evidence with origin of item and what the item is. Take plenty of samples for comparison of clean or unburned carpet if carpet is used for fire evidence or arson cases you will have to show places of the carpet that were not burned. When collecting gashouse items make sure to label the paint can properly with the name of the evidence and send the labelled paint cans to the laboratory with a chain of custody. Flammable residues can be removed from paint cans by using a syringe. Other evidence such as cigarettes, matches, gas cans, accelerants and other items need to be photographed, label, measured, and then stored inside of clean labelled paint cans.
References
Fisher, Berry A. (2004) CRC Press, Techniques of Crime Scene Investigation
Saferstein Richard (2007) Pearson Prentice Hall, Criminalistics, An Introduction To Forensic Science Tenth Edition
No comments:
Post a Comment