Pulsed discharge ionization detector

Last updated

A pulsed discharge ionization detector (pulsed discharge detector) is a detector for gas chromatography that utilizes a stable, low powered, pulsed DC discharge in helium as an ionization source. [1] [2] [3] [4]

Gas chromatography common type of chromatography

Gas chromatography (GC) is a common type of chromatography used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition. Typical uses of GC include testing the purity of a particular substance, or separating the different components of a mixture. In some situations, GC may help in identifying a compound. In preparative chromatography, GC can be used to prepare pure compounds from a mixture.

Glow discharge plasma formed by the passage of electric current through a gas

A glow discharge is a plasma formed by the passage of electric current through a gas. It is often created by applying a voltage between two electrodes in a glass tube containing a low-pressure gas. When the voltage exceeds a value called the striking voltage, the gas ionization becomes self-sustaining, and the tube glows with a colored light. The color depends on the gas used.

Helium Chemical element with atomic number 2

Helium is a chemical element with symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas, the first in the noble gas group in the periodic table. Its boiling point is the lowest among all the elements. After hydrogen, helium is the second lightest and second most abundant element in the observable universe, being present at about 24% of the total elemental mass, which is more than 12 times the mass of all the heavier elements combined. Its abundance is similar to this figure in the Sun and in Jupiter. This is due to the very high nuclear binding energy of helium-4 with respect to the next three elements after helium. This helium-4 binding energy also accounts for why it is a product of both nuclear fusion and radioactive decay. Most helium in the universe is helium-4, the vast majority of which was formed during the Big Bang. Large amounts of new helium are being created by nuclear fusion of hydrogen in stars.

Contents

Eluants from the GC column, flowing counter to the flow of helium from the discharge zone, are ionized by photons from the helium discharge. Bias electrode(s) focus the resulting electrons toward the collector electrode, where they cause changes in the standing current which are quantified as the detector output.

Electron subatomic particle with negative electric charge

The electron is a subatomic particle, symbol
e−
 or
β−
, whose electric charge is negative one elementary charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no known components or substructure. The electron has a mass that is approximately 1/1836 that of the proton. Quantum mechanical properties of the electron include an intrinsic angular momentum (spin) of a half-integer value, expressed in units of the reduced Planck constant, ħ. As it is a fermion, no two electrons can occupy the same quantum state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of both particles and waves: they can collide with other particles and can be diffracted like light. The wave properties of electrons are easier to observe with experiments than those of other particles like neutrons and protons because electrons have a lower mass and hence a longer de Broglie wavelength for a given energy.

Electron capture mode

In the electron capture mode, the PDD is a selective detector for monitoring high electron affinity compounds such as freons, chlorinated pesticides, and other halogen compounds. For this type of compound, the minimum detectable quantity (MDQ) is at the femtogram () or picogram () level. The PDD is similar in sensitivity and response characteristics to a conventional radioactive ECD, and can be operated at temperatures up to 400°C. For operation in this mode, and are introduced just upstream from the column exit.

Electron capture Process in which a proton-rich nuclide absorbs an inner atomic electron

Electron capture is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shell. This process thereby changes a nuclear proton to a neutron and simultaneously causes the emission of an electron neutrino.

Freon is a registered trademark of The Chemours Company, which uses it for a number of halocarbon products. They are stable, nonflammable, moderately toxic gases or liquids which have typically been used as refrigerants and as aerosol propellants. These include the chlorofluorocarbons (CFCs) that cause ozone depletion, and HCFC. Not all refrigerants of this type are labelled as "Freon" since Freon is a brand name for the refrigerants R-12, R-13B1, R-22, R-410A, R-502, and R-503 manufactured by The Chemours Company. The term "freon" is a common descriptor or proprietary eponym like "xerox" or "kleenex." It is commonly used when referring to any fluorocarbon refrigerants.

Pesticide substance used to destroy pests

Pesticides are substances that are meant to control pests, including weeds. The term pesticide includes all of the following: herbicide, insecticides nematicide, molluscicide, piscicide, avicide, rodenticide, bactericide, insect repellent, animal repellent, antimicrobial, and fungicide. The most common of these are herbicides which account for approximately 80% of all pesticide use. Most pesticides are intended to serve as plant protection products, which in general, protect plants from weeds, fungi, or insects.

Helium photoionization mode

In the helium photoionization mode, the PDD is a universal, non-destructive, high sensitivity detector. The response to both inorganic and organic compounds is linear over a wide range. Response to fixed gases is positive (increase in standing current), with an MDQ in the low ppb range. The PDD in helium photoionization mode is an excellent replacement for flame ionization detectors in petrochemical or refinery environments, where the flame and use of hydrogen can be problematic. In addition, when the helium discharge gas is doped with a suitable noble gas, such as argon, krypton, or xenon (depending on the desired cutoff point), the PDD can function as a specific photoionization detector for selective determination of aliphatics, aromatics, amines, as well as other species.

Photoionization ion formation via a photon interacting with a molecule or atom

Photoionization is the physical process in which an ion is formed from the interaction of a photon with an atom or molecule.

Flame ionization detector Type of gas detector used in gas chromatography

A flame ionization detector (FID) is a scientific instrument that measures analyte in a gas stream. It is frequently used as a detector in gas chromatography. The measurement of ion per unit time make this a mass sensitive instrument. Standalone FIDs can also be used in applications such as landfill gas monitoring, fugitive emissions monitoring and internal combustion engine emissions measurement in stationary or portable instruments.

Hydrogen Chemical element with atomic number 1

Hydrogen is a chemical element with symbol H and atomic number 1. With a standard atomic weight of 1.008, hydrogen is the lightest element in the periodic table. Hydrogen is the most abundant chemical substance in the Universe, constituting roughly 75% of all baryonic mass. Non-remnant stars are mainly composed of hydrogen in the plasma state. The most common isotope of hydrogen, termed protium, has one proton and no neutrons.

Related Research Articles

Ionization or ionisation, is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule is called an ion. Ionization can result from the loss of an electron after collisions with subatomic particles, collisions with other atoms, molecules and ions, or through the interaction with electromagnetic radiation. Heterolytic bond cleavage and heterolytic substitution reactions can result in the formation of ion pairs. Ionization can occur through radioactive decay by the internal conversion process, in which an excited nucleus transfers its energy to one of the inner-shell electrons causing it to be ejected.

Geiger–Müller tube

The Geiger–Müller tube or G–M tube is the sensing element of the Geiger counter instrument used for the detection of ionizing radiation. It was named after Hans Geiger, who invented the principle in 1908, and Walther Müller, who collaborated with Geiger in developing the technique further in 1928 to produce a practical tube that could detect a number of different radiation types.

Mass spectrometry analytical technique based on determining mass to charge ratio of ions

Mass spectrometry (MS) is an analytical technique that ionizes chemical species and sorts the ions into a spectrum based on their mass-to-charge ratio. In simpler terms, a mass spectrum measures the masses within a sample. Mass spectrometry is used in many different fields and is applied to pure samples as well as complex mixtures.

Ion source Device that creates charged atoms and molecules (ions)

An ion source is a device that creates atomic and molecular ions. Ion sources are used to form ions for mass spectrometers, optical emission spectrometers, particle accelerators, ion implanters and ion engines.

Gas chromatography–mass spectrometry analytical method

Gas chromatography–mass spectrometry (GC-MS) is an analytical method that combines the features of gas-chromatography and mass spectrometry to identify different substances within a test sample. Applications of GC-MS include drug detection, fire investigation, environmental analysis, explosives investigation, and identification of unknown samples, including that of material samples obtained from planet Mars during probe missions as early as the 1970s. GC-MS can also be used in airport security to detect substances in luggage or on human beings. Additionally, it can identify trace elements in materials that were previously thought to have disintegrated beyond identification. Like liquid chromatography–mass spectrometry, it allows analysis and detection even of tiny amounts of a substance.

Chemical ionization Ionization technique used in mass spectroscopy

Chemical ionization (CI) is a soft ionization technique used in mass spectrometry. This was first introduced by Burnaby Munson and Frank H. Field in 1966. This technique is a branch of gaseous ion-molecule chemistry. Reagent gas molecules are ionized by electron ionization, which subsequently react with analyte molecules in the gas phase in order to achieve ionization. Negative chemical ionization (NCI), charge-exchange chemical ionization and atmospheric-pressure chemical ionization (APCI) are some of the common variations of this technique. CI has several important applications in identification, structure elucidation and quantitation of organic compounds. Beside the applications in analytical chemistry, the usefulness in chemical ionization extends toward biochemical, biological and medicinal fields as well.

Liquid chromatography–mass spectrometry

Liquid chromatography–mass spectrometry (LC-MS) is an analytical chemistry technique that combines the physical separation capabilities of liquid chromatography with the mass analysis capabilities of mass spectrometry (MS). Coupled chromatography - MS systems are popular in chemical analysis because the individual capabilities of each technique are enhanced synergistically. While liquid chromatography separates mixtures with multiple components, mass spectrometry provides structural identity of the individual components with high molecular specificity and detection sensitivity. This tandem technique can be used to analyze biochemical, organic, and inorganic compounds commonly found in complex samples of environmental and biological origin. Therefore, LC-MS may be applied in a wide range of sectors including biotechnology, environment monitoring, food processing, and pharmaceutical, agrochemical, and cosmetic industries.

Residual gas analyzer

A residual gas analyzer (RGA) is a small and usually rugged mass spectrometer, typically designed for process control and contamination monitoring in vacuum systems. Utilizing quadrupole technology, there exists two implementations, utilizing either an open ion source (OIS) or a closed ion source (CIS). RGAs may be found in high vacuum applications such as research chambers, surface science setups, accelerators, scanning microscopes, etc. RGAs are used in most cases to monitor the quality of the vacuum and easily detect minute traces of impurities in the low-pressure gas environment. These impurities can be measured down to Torr levels, possessing sub-ppm detectability in the absence of background interferences.

Atmospheric-pressure chemical ionization

Atmospheric pressure chemical ionization (APCI) is an ionization method used in mass spectrometry which utilizes gas-phase ion-molecule reactions at atmospheric pressure (105 Pa), commonly coupled with high-performance liquid chromatography (HPLC). APCI is a soft ionization method similar to chemical ionization where primary ions are produced on a solvent spray. The main usage of APCI is for polar and relatively less polar thermally stable compounds with molecular weight less than 1500 Da. The application of APCI with HPLC has gained a large popularity in trace analysis detection such as steroids, pesticides and also in pharmacology for drug metabolites.

A photoionization detector or PID is a type of gas detector.

Many gas chromatograph detectors are ion detectors with varying methods of ionizing the components eluting from the gas chromatograph's column.

In mass spectrometry, direct analysis in real time (DART) is an ion source that produces electronically or vibronically excited-state species from gases such as helium, argon, or nitrogen that ionize atmospheric molecules or dopant molecules. The ions generated from atmospheric or dopant molecules undergo ion-molecule reactions with the sample molecules to produce analyte ions. Analytes with low ionization energy may be ionized directly. The DART ionization process can produce positive or negative ions depending on the potential applied to the exit electrode.

The thermal conductivity detector (TCD), also known as a katharometer, is a bulk property detector and a chemical specific detector commonly used in gas chromatography. This detector senses changes in the thermal conductivity of the column effluent and compares it to a reference flow of carrier gas. Since most compounds have a thermal conductivity much less than that of the common carrier gases of helium or hydrogen, when an analyte elutes from the column the effluent thermal conductivity is reduced, and a detectable signal is produced.

Electron capture ionization is the ionization of a gas phase atom or molecule by attachment of an electron to create an ion of the form A. The reaction is

A chromatography detector is a device used in gas chromatography (GC) or liquid chromatography (LC) to detect components of the mixture being eluted off the chromatography column. There are two general types of detectors: destructive and non-destructive. The destructive detectors perform continuous transformation of the column effluent with subsequent measurement of some physical property of the resulting material. The non-destructive detectors are directly measuring some property of the column eluent and thus affords greater analyte recovery.

Direct electron ionization liquid chromatography–mass spectrometry interface

A direct electron ionization liquid chromatography–mass spectrometry interface is a technique for coupling liquid chromatography and mass spectrometry (LC-MS) based on the direct introduction of the liquid effluent into an electron ionization (EI) source. Library searchable mass spectra are generated. Gas-phase EI has many applications for the detection of HPLC amenable compounds showing minimal adverse matrix effects. The direct-EI LC-MS interface provides access to well-characterized electron ionization data for a variety of LC applications and readily interpretable spectra from electronic libraries for environmental, food safety, pharmaceutical, biomedical, and other applications.

Photoelectrochemical processes are processes in photoelectrochemistry; they usually involve transforming light into other forms of energy. These processes apply to photochemistry, optically pumped lasers, sensitized solar cells, luminescence, and photochromism.

Resonance ionization

Resonance ionization is a process in optical physics used to excite a specific atom beyond its ionization potential to form an ion using a beam of photons irradiated from a pulsed laser light. In resonance ionization, the absorption or emission properties of the emitted photons are not considered, rather only the resulting excited ions are mass-selected, detected and measured. Depending on the laser light source used, one electron can be removed from each atom so that resonance ionization produces an efficient selectivity in two ways: elemental selectivity in ionization and isotopic selectivity in measurement.

References

  1. ↑ W. E. Wentworth et al., "Pulsed Discharge Helium Ionization Detector ", Chromatographia, Volume 34, September/October 1992, Numbers 5-8, Pages 219-225
  2. ↑ W. E. Wentworth et al., "Pulsed Discharge Helium Ionization Detector - Universal Detector for Inorganic and Organic Compounds at the Low Picogram Level ", Journal of Chromatography A, Volume 688, Issues 1-2, 30 December 1994, Pages 135-152
  3. ↑ D. S. Forsyth, "Pulsed Discharge Detector: Theory and Applications", Journal of Chromatography A, Volume 1050, Issue 1, 24 September 2004, Pages 63–68
  4. ↑ Wentworth, W. E.; Vasnin, S. V.; Stearns, S. D.; Meyer, C. J. (Sep 1992). "Pulsed discharge helium ionization detector". Chromatographia. 34 (5–8): 219–225. doi:10.1007/bf02268349. ISSN   0009-5893.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.