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Gas Chromatograph-Mass Spectrometer

Gas Chromatograph-Mass Spectrometer

LAURIE DUNCAN

The gas chromatograph-mass spectrometer (GC/MS) is an instrument used to analyze the molecular and ionic composition of chemical compounds. GC/MS technology combines two widely used laboratory techniques: gas chromatography (GC), which separates and identifies compounds in complex mixtures, and mass spectrometry (MS), which determines the molecular weight and ionic components of individual compounds. The combination of these two powerful tools into a single instrumentthe chemical separates produced by the gas chromatograph become the input for the mass spectrometerallows for quick, precise analyses of solid, liquid and gaseous chemical compounds.

Scientists from a wide range of fields currently use GC/MS to identify and analyze inorganic, organic, and bio-organic chemicals. Academic researchers have long used either gas chromatography or mass spectrometry to assess experimental outcomes, analyze biochemical reactions, and age-date geological samples; many of these theoretical and experimental scientists have adopted the newer, more precise, and faster GC/MS technology to replace the two separate instruments. Industrial applications of GC/MS include pharmaceutical drug discovery and testing, process monitoring in the petroleum, chemical, and pharmaceutical industries, and identification of unknown chemicals in applied forensic, military, and environmental sciences.

Gas chromatography is a technique for separating closely-related compounds (solutes) from a liquid or gaseous mixture. (Solids must be vaporized or liquefied before analysis.) GC is most commonly used to separate and detect volatile and semi-volatile organic compounds (VOCs and SVOCs) with molecular weights less than 500 atomic mass units (amu). Although chemists have probably used rudimentary chromatography to separate mixtures since the Middle Ages, the modern chromatograph was not developed until 1941 when British biochemists Archer Martin and Richard Synge invented a chromatographic method that allowed for precise partitioning and detection. Martin and Synge were awarded the 1952 Nobel Prize in chemistry for their efforts.

The GC component of a GC/MS system includes a carrier gas supply, a sample introduction inlet, a capillary column coated with a stationary liquid or solid, and an outlet to the detection system, in this case a mass spectrometer. To begin analysis, a GC/MS technician vaporizes the sample, or analyte, and introduces it into the chromatograph by syringe injection through a rubber septum. A flow of inert carrier gas like helium, argon, or nitrogen moves the analyte into the separation column. Partitioning occurs as the gaseous components of the original analyte assume different velocities when confronted with the column's liquid or solid coating. Partitioning behavior is temperature-dependent, and precise temperature control is an important part of the GC process. A filter removes the separated compounds from the carrier gas at the end of the column before they are fed into the mass spectrometer for individual analysis.

Mass spectrometry is a method of determining the molecular weights of a chemical compound's component ions. (Ions are electrically charged atoms or groups of atoms, and sub-particles of molecules.) The MS instrument, known as the "smallest scale in the world", provides a graph, or mass spectrum, with peaks that indicate the relative amount of each type of ion within a compound. Today's MS systems are based on Sir J. J. Thomson's research at the Cavendish Laboratory at the University of Cambridge. Thomson discovered the electron in 1897, and went on to observe that the parabolic paths of ions traveling through electrical and magnetic fields vary according to the ions' mass-to-charge (m/z) ratios. His experimental instruments were the first mass spectrometers, and he was awarded the 1906 Nobel Prize in physics for his discoveries.

MS instrumentation has become increasingly accurate and complex since Thomson's time, but the principles of the technique and its basic components have remained the same. The MS component of a GC/MS system includes a sample inlet into a vacuum-sealed chamber that houses an ionization source, a mass analyzer, and an ion detector. In a GC/MS system the input sample is always a chemically homogenous gas produced by the GC component that can be introduced directly to the ionizer. Once ionized, the partitioned compound moves into the mass analyzer where the ions travel through an electrical or magnetic field that sorts them according to their m/z ratios. The detector measures the beam of now-separated ions arriving at the end of the analyzer, and converts changes in its intensity to produce the mass spectrum. A sample's mass spectrum is then displayed, catalogued, and compared to a library of known mass spectra by a computer data

system. For many applications, environmental monitoring or drug testing at sporting events, for examples, an unknown sample can be identified using a fairly short list of possible spectra. Other applications, like theoretical chemistry, organic chemistry, or planetary exploration may require an enormous library of possible molecules for identification, and may even produce previously unknown molecules.

Improvements in the individual GC and MS components, electronic automation, and computer data analysis and storage have led to machines that can analyze ever more complex, fragile, and tiny chemical components; GC/MS can now be used to quickly analyze proteins, DNA, and even viruses, and has become a common technique in molecular biology and medical science. GC/MS instruments are also becoming smaller and less expensive, and field laboratory and even portable, suitcase-sized systems that can be used to analyze forensic samples, environmental contaminants, and unknown agents of chemical and biological warfare on site now exist. Remotely operated GC/MS systems are planned components of future space exploration expeditions that hope to characterize the chemical makeup of extra-terrestrial environments, and to search for organic material elsewhere in our solar system.

FURTHER READING:

ELECTRONIC:

Massachusetts Institute of Technology. "Present Life: Spectroscopic Analysis Gas Chromatography/Mass Spectrometry (GC/MS)." Mars Mission 2004, student final presentation. December 10, 2000. <http://web.mit.edu/12.000/www/finalpresentation/experiments/index.html>(January 5, 2003).

Scripps Center for Mass Spectrometry (BC-007), 10550 North Torrey Pines Rd., La Jolla, CA 92037. (858) 7849596. Gary Suizdak, director. <http://masspec.scripps.edu/information/intro/index.html.> (January 5,2003).

Signature Science, LLC8329 North Mopac Blvd Austin, TX 78759. (512) 5332022. Cassandra Hutson, staff chemist. <http://www.signaturescience.com.> (January 8, 2003).

United States Environmental Protection Agency. "Technology: Gas Chromatography." January 2001. <http://fate.clu-in.org/gc.asp?techtypeid=44> (January 9, 2003).

SEE ALSO

Air Plume and Chemical Analysis
Biological Warfare
Isotopic Analysis
Microbiology: Applications to Espionage, Intelligence and Security

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Gas Chromatograph-mass Spectrometer

Gas Chromatograph-mass Spectrometer

In a forensic examination, some sample material can be evaluated at the scene of the accident of crime. Other material, however, needs to be collected and taken to a dedicated laboratory for more sophisticated analyses using a variety of analytical instruments. In 1976, scientists William Keith Hadley and J. A. Zoro, in the United Kingdom, first suggested the use of gas chromatography/mass spectroscopy for forensic purposes and the instrument is now used for a variety of forensic purposes.

The GC/MS instrument helps separate and determine the individual elements and molecules in a sample. The GC/MS provides forensic investigators the ability to identify individual substances that may be found within a very small test sample. Forensic applications of GC/MS include identification and detection of explosives ; investigations of arson , fire, and blasts or explosions; environmental analysis; and drug detection. In recent years, GC/MS has begun to be used in airport security areas as a means of detecting dangerous substances in luggage, on animals who are traveling, or on human beings. Because of its great sensitivity, gas chromatography/mass spectroscopy can be utilized to identify trace elements in either minute amounts of substances or in substances that were believed to be contaminated or to be degraded beyond usability.

The GC/MS is comprised of two parts: the gas chromatograph and the mass spectrometer. The gas chromatograph functions by separating the molecules within the sample compound into their most elemental particles, allowing some types of molecules to pass into the mass spectrometer more rapidly than others. When the molecules move into the mass spectrometer, they are broken down into ionized fragments, and then each molecule is specifically identified based on mass and ionic charge.

Gas chromatography is a technique for separating closely related compounds (solutes) from a liquid or gaseous mixture. (Solids must be vaporized or liquefied before analysis.) Gas chromatography is most commonly used to separate and detect volatile and semi-volatile organic compounds (VOCs and SVOCs) with molecular weights less than 500 atomic mass units (amu). Although chemists have probably used rudimentary chromatography to separate mixtures since the Middle Ages, the modern chromatograph was not developed until 1941, when British biochemists Archer Martin and Richard Synge invented a chromatographic method that allowed for precise partitioning and detection. Martin and Synge were awarded the 1952 Nobel Prize in Chemistry for their efforts.

The GC component of a GC/MS system includes a carrier gas supply, a sample introduction inlet, a capillary column coated with a stationary liquid or solid, and an outlet to the detection system, in this case a mass spectrometer. To begin analysis, a GC/MS technician vaporizes the sample, or analyte, and introduces it into the chromatograph by syringe injection through a rubber septum. A flow of inert carrier gas like helium, argon, or nitrogen moves the analyte into the separation column. Partitioning occurs as the gaseous components of the original analyte assume different velocities when confronted with the column's liquid or solid coating. Partitioning behavior is temperature dependent, and precise temperature control is an important part of the GC process. A filter removes the separated compounds from the carrier gas at the end of the column before they are fed into the mass spectrometer for individual analysis.

Mass spectroscopy is a method of determining the molecular weights of a chemical compound's component ions. (Ions are electrically charged atoms or groups of atoms, and sub-particles of molecules.) The MS instrument, which has been called the smallest scale in the world, provides a graph, or mass spectrum, with peaks that indicate the relative amount of each type of ion within a compound. Today's MS systems are based on Sir J. J. Thomson's research at the Cavendish Laboratory at the University of Cambridge. Thomson discovered the electron in 1897, and went on to observe that the parabolic paths of ions traveling through electrical and magnetic fields vary according to the ions' mass-to-charge (m/z) ratios. His experimental instruments were the first mass spectrometers, and he was awarded the 1906 Nobel Prize in Physics for his discoveries.

Mass spectroscopy instrumentation has become increasingly accurate and complex since Thomson's time, but the principles of the technique and its basic components have remained the same. The MS component of a GC/MS system includes a sample inlet into a vacuum-sealed chamber that houses an ionization source, a mass analyzer, and an ion detector. In a GC/MS system, the input sample is always a chemically-homogenous gas produced by the GC component that can be introduced directly to the ionizer. Once ionized, the partitioned compound moves into the mass analyzer where the ions travel through an electrical or magnetic field that sorts them according to their m/z ratios. The detector measures the beam of now-separated ions arriving at the end of the analyzer, and converts changes in its intensity to produce the mass spectrum. A sample's mass spectrum is then displayed, catalogued, and compared to a library of known mass spectra by a computer data system.

Improvements in the individual GC and MS components, electronic automation, and computer data analysis and storage have led to machines that can analyze ever more complex, fragile, and tiny chemical components; GC/MS can now be used to quickly analyze proteins, DNA , and even viruses, and has become a common technique in molecular biology and medical science. GC/MS instruments are also becoming smaller and less expensive, and field laboratory and even portable, suitcase-sized systems that can be used to analyze forensic samples on site now exist.

One of the reasons that the GC/MS test has a great deal of value in the world of forensic substance identification has to do with its specificity: the GC/MS can positively identify the presence of a suspected poison or other substance. The portability of GC/MS test equipment allows it to be taken directly from a crime scene to the area where a suspect is detained to immediately perform tests on a suspect's tissue, serology (blood ), clothing, etc.

see also Accelerant; Analytical instrumentation; Arson; Breathalyzer®; Chemical and biological detection technologies; Control samples; Fourier transform infrared spectrophotometer (FTIR); Micro-fourier transform infrared spectrometry.

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gas–liquid chromatography

gas–liquid chromatography A technique for separating or analysing mixtures of gases by chromatography. The apparatus consists of a very long tube containing the stationary phase, a nonvolatile liquid, such as a hydrocarbon oil coated on a solid support. The sample is often a volatile liquid mixture (e.g. of fatty acids), which is vaporized and swept through the column by a carrier gas (e.g. hydrogen). The components of the mixture pass through the column at different rates and are detected as they leave, either by measuring the thermal conductivity of the gas or by a flame detector.

Gas chromatography is usually used for analysis; components can be identified by the time they take to pass through the column. It is also used for separating mixtures into their components, which are then directly injected into a mass spectrometer in the technique of gas chromatography–mass spectroscopy.

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gas chromatography

gas chromatography An analytical technique in which the components of a sample are separated by partitioning between either a mobile gas and a thin layer of non-volatile liquid held on a solid support (gas–liquid chromatography) or between the gas and a solid absorbent as the stationary phase (gas–solid chromatography). Partitioning occurs repeatedly throughout the column, and, as each solute travels at its own rate, a band corresponding to each solute will form. Solutes are eluted (washed out) in increasing order of partition ratio, and enter a detector attached to the column exit. The time of emergence of a peak on the display identifies a component, and the area under each peak is proportional to the component's concentration. Gas chromatography is used mainly in the analysis of volatile organic compounds.

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gas chromatography

gas chromatography Analytical technique in which the components of a sample are separated by partitioning between either a mobile gas and a thin layer of non-volatile liquid held on a solid support (gas—liquid chromatography), or between the gas and a solid absorbent as the stationary phase (gas—solid chromatography). Partitioning occurs repeatedly throughout the column, and, as each solute travels at its own rate, a band corresponding to each solute will form. Solutes are eluted (washed out) in increasing order of partition ratio, and enter a detector attached to the column exit. The time of emergence of a peak on the display identifies a component, and the area under each peak is proportional to the component's concentration. Gas chromatography is used mainly in the analysis of volatile organic compounds.

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gas—liquid chromatography

gas—liquid chromatography See GAS CHROMATOGRAPHY.

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