Forensic chemistry
The range of different methods is important due to the destructive nature of some instruments and the number of possible unknown substances that can be found at a scene.
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.
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.
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.
[10] Until the early 19th century, there were no methods to accurately determine if a particular chemical was present, and poisoners were rarely punished for their crimes.
[13] A pioneer in the development of forensic microscopy, Orfila contributed to the advancement of this method for the detection of blood and semen.
[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.
Stas's protocol was subsequently altered to incorporate tests for caffeine, quinine, morphine, strychnine, atropine, and opium.
Using spectroscopy, the two scientists were able to identify substances based on their spectrum, providing a method of identification for unknown materials.
[15] The ability to separate mixtures into their individual components allows forensic chemists to examine the parts of an unknown material against a database of known products.
[18] Modern forensic chemists rely on numerous instruments to identify unknown materials found at a crime scene.
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.
[19]: 202 Fellgett also used the Fourier transform, a mathematical method that can break down a signal into its individual frequencies, to make sense of the enormous amount of data received from the complete infrared analysis of a material.
[19] Since then, Fourier transform infrared spectroscopy (FTIR) instruments have become critical in the forensic analysis of unknown material because they are nondestructive and extremely quick to use.
[21] Advancements in the field of chromatography arrived in 1953 with the invention of the gas chromatograph by Anthony T. James and Archer John Porter Martin, allowing for the separation of volatile liquid mixtures with components which have similar boiling points.
Modern HPLC instruments are capable of detecting and resolving substances whose concentrations are as low as parts per trillion.
[22] One of the most important advancements in forensic chemistry came in 1955 with the invention of gas chromatography-mass spectrometry (GC-MS) by Fred McLafferty and Roland Gohlke.
[25] The increase in the sensitivity of instrumentation has advanced to the point that minute impurities within compounds can be detected potentially allowing investigators to trace chemicals to a specific batch and lot from a manufacturer.
FTIR analysis of mixtures, while not impossible, presents specific difficulties due to the cumulative nature of the response.
Radiation in the form of light is then passed through the sample forcing the atoms to jump to a higher energy state.
[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.
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.
[42] The constant creation of new drugs, both legal and illicit, forces toxicologists to keep themselves apprised of new research and methods to test for these novel substances.
[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.
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.
[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.
