page_title: Forensic chemistry
section_title: Modernization
hierarchical_section_title: Forensic chemistry / History / Modernization
caption_attribution_description: English: A gas chromatograph–mass spectrometer (GCMS) with open door - (ThermoQuest Trace 200). The apparatus is the property of CBMiM PAN
context_page_description: Forensic chemistry is the application of chemistry and its subfield, forensic toxicology, in a legal setting. A forensic chemist can assist in the identification of unknown materials found at a crime scene. Specialists in this field have a wide array of methods and instruments to help identify unknown substances. These include high-performance liquid chromatography, gas chromatography-mass spectrometry, atomic absorption spectroscopy, Fourier transform infrared spectroscopy, and thin layer chromatography. 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 prefer using nondestructive methods first, to preserve evidence and to determine which destructive methods will produce the best results.
  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.
context_section_description: 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 monochromator and could only measure light absorption in a very narrow wavelength band.  It was not until the coupling of an interferometer with an IR spectrometer in 1949 by Peter Fellgett that the complete infrared spectrum could be measured at once.  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.  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.  Spectroscopy was further advanced in 1955 with the invention of the modern atomic absorption (AA) spectrophotometer by Alan Walsh.  AA analysis can detect specific elements that make up a sample along with their concentrations, allowing for the easy detection of heavy metals such as arsenic and cadmium.
  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.  Nonvolatile liquid mixtures could be separated with liquid chromatography, but substances with similar retention times could not be resolved until the invention of high-performance liquid chromatography (HPLC) by Csaba Horváth in 1970.  Modern HPLC instruments are capable of detecting and resolving substances whose concentrations are as low as parts per trillion.
  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.  The coupling of a gas chromatograph with a mass spectrometer allowed for the identification of a wide range of substances.  GC-MS analysis is widely considered the "gold standard" for forensic analysis due to its sensitivity and versatility along with its ability to quantify the amount of substance present. 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.
caption: A GC-MS unit with doors open.  The gas chromatograph is on the right and the mass spectrometer is on the left.
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