Forensic chemistry
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Forensic chemistry is the application of
Along with other forensic specialists, forensic chemists commonly testify in court as expert witnesses regarding their findings. Forensic chemists follow a set of standards that have been proposed by various agencies and governing bodies, including the Scientific Working Group on the Analysis of Seized Drugs. In addition to the standard operating procedures proposed by the group, specific agencies have their own standards regarding the quality assurance and quality control of their results and their instruments. To ensure the accuracy of what they are reporting, forensic chemists routinely check and verify that their instruments are working correctly and are still able to detect and measure various quantities of different substances.
Role in investigations
Forensic chemists' analysis can provide leads for investigators, and they can confirm or refute their suspicions. The identification of the various substances found at the scene can tell investigators what to look for during their search. During
Forensic chemists also help to confirm or refute investigators' suspicions in drug or alcohol cases. The instruments used by forensic chemists can detect minute quantities, and accurate measurement can be important in crimes such as driving under the influence as there are specific blood alcohol content cutoffs where penalties begin or increase.[7] In suspected overdose cases, the quantity of the drug found in the person's system can confirm or rule out overdose as the cause of death.[8]
History
Early history
Throughout history, a variety of poisons have been used to commit murder, including
The next advancement in the detection of poisons came in 1850 when a valid method for detecting vegetable alkaloids in human tissue was created by chemist Jean Stas.[14] Stas's method was quickly adopted and used successfully in court to convict Count Hippolyte Visart de Bocarmé of murdering his brother-in-law by nicotine poisoning.[14] Stas was able to successfully isolate the alkaloid from the organs of the victim. Stas's protocol was subsequently altered to incorporate tests for caffeine, quinine, morphine, strychnine, atropine, and opium.[15]
The wide range of instrumentation for forensic chemical analysis also began to be developed during this time period. The early 19th century saw the invention of the
Modernization
Modern forensic chemists rely on numerous instruments to identify unknown materials found at a crime scene. The 20th century saw many advancements in technology that allowed chemists to detect smaller amounts of material more accurately. The first major advancement in this century came during the 1930s with the invention of a spectrometer that could measure the signal produced with infrared (IR) light. Early IR spectrometers used a
Advancements in the field of chromatography arrived in 1953 with the invention of the
One of the most important advancements in forensic chemistry came in 1955 with the invention of
Methods
Forensic chemists rely on a multitude of instruments to identify unknown substances found at a scene.[26] Different methods can be used to determine the identity of the same substance, and it is up to the examiner to determine which method will produce the best results. Factors that forensic chemists might consider when performing an examination are the length of time a specific instrument will take to examine a substance and the destructive nature of that instrument. They prefer using nondestructive methods first, to preserve the evidence for further examination.[27] Nondestructive techniques can also be used to narrow down the possibilities, making it more likely that the correct method will be used the first time when a destructive method is used.[27]
Spectroscopy
The two main standalone spectroscopy techniques for forensic chemistry are FTIR and AA spectroscopy. FTIR is a nondestructive process that uses
Atomic absorption spectroscopy (AAS) is a destructive technique that is able to determine the elements that make up the analyzed sample. AAS performs this analysis by subjecting the sample to an extremely high heat source, breaking the atomic bonds of the substance, leaving free atoms. Radiation in the form of light is then passed through the sample forcing the atoms to jump to a higher energy state.[31]: 2 Forensic chemists can test for each element by using a corresponding wavelength of light that forces that element's atoms to a higher energy state during the analysis.[31]: 256 For this reason, and due to the destructive nature of this method, AAS is generally used as a confirmatory technique after preliminary tests have indicated the presence of a specific element in the sample. The concentration of the element in the sample is proportional to the amount of light absorbed when compared to a blank sample.[32] AAS is useful in cases of suspected heavy metal poisoning such as with arsenic, lead, mercury, and cadmium. The concentration of the substance in the sample can indicate whether heavy metals were the cause of death.[33]
Chromatography
Spectroscopy techniques are useful when the sample being tested is pure, or a very common mixture. When an unknown mixture is being analyzed it must be broken down into its individual parts. Chromatography techniques can be used to break apart mixtures into their components allowing for each part to be analyzed separately.
Thin layer chromatography (TLC) is a quick alternative to more complex chromatography methods. TLC can be used to analyze inks and dyes by extracting the individual components.
High-performance liquid chromatography (HPLC) can be used to extract individual components from a mixture dissolved in a
Forensic toxicology
Forensic toxicology is the study of the pharmacodynamics, or what a substance does to the body, and pharmacokinetics, or what the body does to the substance. To accurately determine the effect a particular drug has on the human body, forensic toxicologists must be aware of various levels of drug tolerance that an individual can build up as well as the therapeutic index for various pharmaceuticals. Toxicologists are tasked with determining whether any toxin found in a body was the cause of or contributed to an incident, or whether it was at too low a level to have had an effect.[39] While the determination of the specific toxin can be time-consuming due to the number of different substances that can cause injury or death, certain clues can narrow down the possibilities. For example, carbon monoxide poisoning would result in bright red blood while death from hydrogen sulfide poisoning would cause the brain to have a green hue.[40][41]
Toxicologists are also aware of the different
Standards
Category A | Category B | Category C |
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Guidelines have been set up by various governing bodies regarding the standards that are followed by practicing forensic scientists. For forensic chemists, the international Scientific Working Group for the Analysis of Seized Drugs (SWGDRUG) presents recommendations for the quality assurance and quality control of tested materials.[45] In the identification of unknown samples, protocols have been grouped into three categories based on the probability for false positives. Instruments and protocols in category A are considered the best for uniquely identifying an unknown material, followed by categories B and then C. To ensure the accuracy of identifications SWGDRUG recommends that multiple tests using different instruments be performed on each sample, and that one category A technique and at least one other technique be used. If a category A technique is not available, or the forensic chemist decides not to use one, SWGDRUG recommends that at least three techniques be used, two of which must be from category B.[45]: 14–15 Combination instruments, such as GC-MS, are considered two separate tests as long as the results are compared to known values individually For example, the GC elution times would be compared to known values along with the MS spectra. If both of those match a known substance, no further tests are needed.[45]: 16
Standards and controls are necessary in the quality control of the various instruments used to test samples. Due to the nature of their work in the legal system, chemists must ensure that their instruments are working accurately. To do this, known controls are tested consecutively with unknown samples.[46] By comparing the readouts of the controls with their known profiles the instrument can be confirmed to have been working properly at the time the unknowns were tested. Standards are also used to determine the instrument's limit of detection and limit of quantification for various common substances.[47] Calculated quantities must be above the limit of detection to be confirmed as present and above the limit of quantification to be quantified.[47] If the value is below the limit the value is not considered reliable.[47]
Testimony
The standardized procedures for testimony by forensic chemists are provided by the various agencies that employ the scientists as well as SWGDRUG. Forensic chemists are ethically bound to present testimony in a neutral manner and to be open to reconsidering their statements if new information is found.[45]: 3 Chemists should also limit their testimony to areas they have been qualified in regardless of questions during direct or cross-examination.[45]: 27
Individuals called to testify must be able to relay scientific information and processes in a manner that lay individuals can understand.[48] By being qualified as an expert, chemists are allowed to give their opinions on the evidence as opposed to just stating the facts. This can lead to competing opinions from experts hired by the opposing side.[48] Ethical guidelines for forensic chemists require that testimony be given in an objective manner, regardless of what side the expert is testifying for.[49] Forensic experts that are called to testify are expected to work with the lawyer who issued the summons and to assist in their understanding of the material they will be asking questions about.[49]
Education
Forensic chemistry positions require a bachelor's degree or similar in a natural or physical science, as well as laboratory experience in general, organic, and analytical chemistry. Once in the position, individuals are trained in protocols performed at that specific lab until they are proven competent to perform all experiments without supervision. Practicing chemists in the field are expected to complete continuing education to maintain their proficiency.[45]: 4–6
References
- ^ a b "A Simplified Guide to Forensic Drug Chemistry" (PDF). National Forensic Science Technology Center. Archived from the original (PDF) on March 21, 2016. Retrieved September 24, 2015.
- ^ Browne, Malcolm W. (April 21, 1995). "Terror in Oklahoma: the Science; Experts Search for Debris to Link Bomb to a Suspect". The New York Times. Retrieved October 28, 2015.
- ^ Stern, Wal (November 1995). "Modern Methods of Accelerant Analysis". Southeast Asia Fire and Security. Retrieved October 28, 2015 – via T.C. Forensic.
- ^ a b "Common Explosives". The National Counterterrorism Center. Archived from the original on January 13, 2016. Retrieved October 28, 2015.
- ^ . Retrieved December 6, 2016.
- ^ Goldstein, Joseph (June 7, 2013). "Woman from Texas is Charged in Ricin Case". The New York Times. Retrieved December 6, 2016.
- ^ "Legal BAC Limits Data by Country". World Health Organization. Retrieved October 30, 2015.
- ^ "Toxicology Screen". The New York Times. Retrieved December 5, 2016.
- ISBN 9780773599895– via Google Books.
- ^ Cellania, Miss (November 3, 2009). "5 Classic Poisons and the People who Used Them". Mental Floss. Retrieved September 24, 2015.
- ^ a b Pizzi, Richard A. (September 2004). "Pointing to Poison" (PDF). Today's Chemist at Work: 43–45. Retrieved September 24, 2015.
- ^ Watson, Stephanie (June 9, 2008). "How Forensic Lab Techniques Work". How Stuff Works. Retrieved September 24, 2015.
- ^ a b "Mathieu Joseph Bonaventure Orfila (1787–1853)". National Library of Medicine. June 5, 2014. Retrieved September 24, 2015.
- ^ PMID 20355192.
- ^ a b "Technologies". National Library of Medicine. June 5, 2014. Retrieved September 25, 2015.
- ^ "Fraunhofer, Joseph von". The Encyclopedia Americana. Vol. 12. The Encyclopedia American Corporation. 1919. p. 28.
- ^ a b "Spectroscopy and the Birth of Astrophysics". American Institute of Physics. Center for History of Physics. Archived from the original on September 7, 2015. Retrieved September 25, 2015.
- ^ a b c d e f g Carlysle, Felicity (2011-07-26). "TLC the Forensic Way". theGIST. Glasgow Insight Into Science & Technology. Archived from the original on July 30, 2016. Retrieved October 10, 2015.
- ^ a b Derrick, Michele R.; Stulik, Dusan; Landry, James M. "Infrared Spectroscopy in Conservation Science" (PDF). The Getty Conservation Institute. Retrieved September 26, 2015.
- PMID 8419043. Retrieved October 6, 2015.
- .
- ISBN 9780444635532– via Google Books.
- ^ Jones, Mark. "Gas Chromatography-Mass Spectrometry". American Chemical Society. Retrieved 19 Nov 2019.
- ^ PMID 24234933.
- PMID 7920539. Retrieved September 27, 2015.
- .
- ^ a b "Quality Assurance Guide for the Forensic Analysis of Ignitable Liquids". Forensic Science Communications. 8 (2). April 2006. Archived from the original on May 29, 2016. Retrieved September 24, 2015.
- ^ Angelos, Sanford; Garry, Mike (August 5, 2011). "Seized Drug Analysis Using FT-IR and Mixture Searching For More Effective Identification". Forensic Magazine. Advantage Business Media. Retrieved October 6, 2015.
- ^ Izzia, Federico; Nunn, Simon; Bradley, Michael (August 1, 2008). "Analysis of Mixtures by FT-IR: Spatial and Spectral Separation of Complex Samples". Spectroscopy Online. Special Issues-08-01-2008. Retrieved October 6, 2015.
- ISBN 9780470093078– via Google Books.
- ^ ISBN 9780444420152– via Google Books.
- ^ Schiller, Matt. "Atomic Absorption Spectroscopy (AAS)". Easy Chem. Retrieved October 7, 2015.
- S2CID 26671861.
- ISBN 9780123848628– via Google Books.
- PMID 15629016.
- ISBN 9780471727897– via Google Books.
- .
- ^ PMID 17579968.
- ^ "Forensic Toxicology". National Institute of Justice. December 23, 2014. Retrieved October 12, 2015.
- ^ Foley, Katherine (August 16, 2015). "The Science Behind Forensic Toxicology". Quartz. Retrieved October 12, 2015.
- PMID 19297107. Retrieved October 12, 2015.
- S2CID 22267781.
- ^ Melinek, Jude (September 2016). "How Designer Drugs and the Opioid Epidemic Affect Modern Forensic Practice". Forensic Magazine: 18–19. Archived from the original on October 1, 2016. Retrieved September 29, 2016.
- ^ a b Stout, Peter; Moore, Katherine; Grabenauer, Megan; Ropero-Miller, Jeri (March 2013). Expansion of a Cheminformatic Database of Spectral Data for Forensic Chemists and Toxicologists (PDF) (Report). U.S. Department of Justice. p. 2. Retrieved December 5, 2016.
- ^ a b c d e f "Scientific Working Group for the Analysis of Seized Drugs (SWGDRUG) Recommendations" (PDF). 7.1. June 9, 2016. Retrieved January 4, 2017.
- ^ "Validation Guidelines for Laboratories Performing Forensic Analysis of Chemical Terrorism". Forensic Science Communications. 7 (2). April 2005. Archived from the original on March 4, 2016. Retrieved October 16, 2015.
- ^ PMID 18852857.
- ^ a b Melton, Lisa (November 2007). "Courtroom chemistry" (PDF). Chemistry World. Retrieved October 13, 2016.
- ^ a b Wells, Doris (March 26, 2012). "In Brief: Law 101: Legal Guide for the Forensic Expert". National Institute of Justice. Retrieved October 13, 2016.