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Glossary
EVISA is providing a list of terms used in the area of speciation and fractionation analysis. Since speciation analysis is a field of analytical chemistry that is specified by a pronounced interdisciplinary cooperation between different sciences such as biochemistry, medicine, biology, environmental sciences, nutritional sciences and material sciences its terminology is a complex mixture of terms used in all these.
You may search for a term or browse the glossary alphabetically.
(In case that you cannot find the term you may consult more special glossaries or handbooks about nomenclature. For more details please consult EVISA's Link pages related to terminology,
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An electrically charged species formed by non-covalent attachment between an ion and a neutral species. These are most commonly observed in desorption and API and CI ion sources where a molecule of a component in the solvent or reagen gas remains attached to the ion.
Source: A. Mallet, S. Down, Dictionary of Mass Spectrometry, Wiley, 2010
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A general term describing mass spectrometry in which ionisation takes place at ambient pressure and temperature, usually in the open air. Specific types include DESI and DART.
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Accelerator mass spectrometry (AMS). In this specialized method, atomic ions are formed from the sample by charge stripping in a very high voltage source, usually coupled to a Van de Graff accelerator. Accelerator mass spectrometry is used for low-level analysis of 14 C isotopes in radiocarbon dating and biological tracer studies.
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The field of mass spectrometry dealing with organic materials derived from biological systems. The spectrometry is different from organic mass spectrometry in that organic molecules are analyzed from the standpoint of biological function and the life sciences.
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CI is a relatively soft
ionization method used for mass spectrometry. In positive-ion mode, ionization is
effected by ion-molecule reactions occurring between ions generated by
electron ionization (EI) of a reagent gas and the neutral molecules of the
analyte.
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A transmission hexapole or octapole collision cell to which an oscillating radio frequency potential is applied that is used for charge exchange neutralization of interfering ions in inductively coupled plasma mass spectrometry.
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Consecutive reaction monitoring (CRM) is the application of selected
reaction monitoring to sequential fragmentation in three or more stages
of mass spectrometry. The product ion from the first stage of mass spectrometry becomes the precursor ion for the second stage, and so on.
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Continuous flow fast atom bombardment is a variant of the fast atom
bombardment ionization technique for mass spectrometry in which the analyte is dissolved in a liquid matrix that is
continuously supplied to the sample probe tip.
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Direct analysis in real time by mass spectrometry; it is a proprietary term indicating the formation of ions from a solid or liquid sample at atmospheric pressure through the interaction of a gas stream containing internally excited atoms or molecules with the surface.
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Delayed extraction is an experimental technique in time-of-flight mass spectrometry in which improved mass resolution is obtained by using a controlled time delay between the initial pulse of ion formation and acceleration of the ions into the flight tube of the instrument. The technique is also called time-lag focusing.
  
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Desorption ionization (DI) is a general term used to group various methods (secondary ion mass spectrometry, fast atom bombardment, californium fission fragment desorption, and plasma desorption) in which ions are generated directly from a sample by rapid energy input into the condensed phase sample. There may be no discrete process of desorption (in the thermal sense), but instead a transfer of usually nonvolatile sample molecules into the gas phase as ions that can subsequently be mass-analyzed.
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SIMS analysis with primary ion current density (corresponding to SIMS gun flux) of several µA/cm2 or more. Primarily used in component analysis of sample surface layers in the depth direction.
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Electron impact ionization or as currently preferred electron ionization
represents the classical method of ion generation in mass spectrometry. The analyte is
introduced into the evacuated ion source (<10-6 mbar) and subsequently ionized by collisions with energetic electrons (routine 70 eV) generated by thermal emission from a
heated filament.
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A mass spectrometric technique for liquid samples that involves preparing electrically charged droplets from analyte molecules dissolved in a solvent. The electrically charged droplets enter a vacuum chamber where the solvent is evaporated. Evaporation of solvent reduces the droplet size, thereby increasing the coulombic repulsion within the droplet. As the charged droplets get smaller, the excess charge within them causes them to disintegrate and release analyte molecules. The volatilized analyte molecules are then analyzed by mass spectrometry.
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In elemental mass spectrometry, a technique used mostly for inorganic
materials, the elemental composition of a sample is determined
rather
than the structural identities of its chemical constituents.
Elemental
mass spectrometry provides quantitative information about the
concentrations
of those elements. The ion source used in elemental MS is
ordinarily
an atmospheric-pressure discharge such as the inductively
coupled plasma
(ICP) or a moderate-power device such as the glow-discharge
source.
In either case, the decomposition of the sample into its
constituent
atoms and ionization of those atoms occurs in a specially
designed source.
The resulting atomic-ion beam is then separated or sorted by a
mass
spectrometer and the signal as a function of m/z used to
determine the
sample composition.
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A mass spectrometric technique that is used for the analysis of a wide
range of biomolecules, such as glycoalkaloids, glycoproteins,
polysaccharides, and peptides. Positive and negative fast atom
bombardment spectra are recorded on a mass spectrometer fitted with an
atom gun with xenon as the customary beam. The mass spectra obtained
contain molecular weight recognition as well as sequence information.
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Flow injection mass spectrometry is a variant of flow injection
analysis in which a plug of sample is injected into a liquid carrier
stream for on-line analysis by mass spectrometry. This term is synonymous with flow injection analysis mass spectrometry.
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GC-MS is a hyphenated technique in which a gas-chromatograph is coupled to a mass spectrometer.
GC-MS can be combined with any ionization method suitable to ionize
neutral molecules in the gas phase but in practice electron
ionization (EI) and chemical ionization (CI) in both positive and
negative ion modes are the methods of choice.
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GC-ICP-MS is a hyphenated technique in which a gas-chromatograph is
coupled to the sample inlet of an inductively coupled plasma (ICP) used
as the ionization source for mass spectrometry. Depending on the type
of the mass spectrometer, one or many elements can be monitored in the
GC effluent, obtaining element selective information within the
chromatograms.
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Low-pressure (typically millitorr) discharge that expands to cover essentially the entire surface of an electrode rather than condensing into a narrow arc channel. The glow discharge source (GDS) is used as a source both for atomic emission specrometry (GDOES) or mass spectrometry (GDMS).
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ICP-MS (Inductively Coupled Plasma Mass Spectrometry) is a type of mass spectrometry that is highly sensitive and capable of simultaneous determination of a range of elements at below one part in 10 12. It is based on coupling together an inductively coupled plasma as an ion source with a mass spectrometer as a detection system for ions.
The ions generated within the plasma at atmospheric pressure are extracted through a series of cones into the vacuum chamber of a mass spectrometer, usually a quadrupole. Other mass analyzers coupled to ICP systems include double focusing magnetic-electric sector systems with both single and multiple collector, as well as time-of-flight (TOF) systems (both with axial and orthogonal accelerators). In any case the ions are separated on the basis of their mass-to-charge ratio and a detector receives an ion signal proportional to the concentration.
The concentration of a sample can be determined through calibration with elemental standards (external calibration). Accuracy and precision can be enhanced by using internal standards and rationing the measurements against these. ICP-MS also lends itself to quantitative determinations through isotope dilution analysis, a single point method based on an isotopically enriched standard.
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In a MALDI-TOF instrument, the incident laser desorption and ionising beam can be rastered over a two-dimensional surface. Similarly, in TOF SIMS, the impacting ion beam is rastered. Diagnostic ions specific to target molecules are detected and their abundance is converted into an image reflecting their intensities within the material being analysed. This development has important applications in biological and medical studies and has been used as a complementary technique to microscopy for tissue sections. Also known as ion imaging.
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The inductively coupled plasma (ICP) is the most widely used source for atomic emission and inorganic mass spectrometry. A "flame-like" plasma is sustained by means of a radiofrequency electric current via an induction coil (electrode-less) within a flowing plasma gas (mostly argon, but other gases such as Helium, Nitrogen or Air are principally possible). The plasma gas is transported into the discharge region via a quartz torch providing different channels structuring the gas-flow so that the high temperature plasma (ionised argon) does not melt the discharge container and the sample stream can be injected into the highly viscous plasma. The plasma with its very high temperature in the range of 7000-8000K efficiently desolvates, vaporizes, dissociates, atomizes, excites, and ionizes samples introduced as gases, vapors or aerosols. In this way, the ICP can be used as an atomizer and excitation source for atomic spectrometry (AES, AFS) or as an ion source for mass spectrometry ( ICP-MS).
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When the change in the isotopic abundances of an element are a regular function of the mass
difference between the isotopes. Physical or chemical processes can induce such changes.
These changes may result from natural or anthropogenic processes and even from the
measurement process itself.. Both the mass spectrometer ion source, the detector and the
techniques used to prepare samples for mass spectrometry can introduce isotopic (mass)
fractionation.. The magnitude of this effect usually increases with increasing fractional mass
difference between the isotopes. Consequently the magnitude of the effect is greater for elements
with smaller atomic numbers.
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In isotope ratio mass spectrometry (IRMS), element isotope ratios are
determined
very accurately and precisely. Typically, single focusing
magnetic sector
mass spectrometers with fixed multiple detectors (one per
isotope) are
used. Complex compounds are reduced to simple molecules prior
to measurement,
for example, organic compounds are combusted to CO2,
H2O
and N2.
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Laser desorption/ionization mass spectrometry, particularly emphasizing spatially resolved composition information.
(see also: LAMMA)
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LC-MS is a hyphenated technique in which a liquid chromatograph is
coupled with a mass spectrometric analyzer. For coupling the LC
operated at atmospheric pressure with the high vacuum mass analyzer a
lot of different interfaces have been designed ranging from moving belt
over continuous-flow FAB, frit-FAB to ESI and APCI, with ESI and APCI
being the most successful interfaces.
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Matrix assisted laser desorption ionization mass spectrometry (MALDI) is a mass spectrometric technique that is used for the analysis of large
biomolecules. Analyte molecules are embedded in an excess matrix of
small organic molecules that show a high resonant absorption at the
laser wavelength used. The matrix absorbs the laser energy, thus
inducing a soft disintegration of the sample-matrix mixture into free
(gas phase) matrix and analyte molecules and molecular ions. In general,
only molecular ions of the analyte molecules are produced and almost no
fragmentation occurs. This makes the method well suited for molecular
weight determinations and mixture analysis.
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The term mass defect has an “official” meaning that is quite different from one of its meanings in mass spectrometry. Officially, the mass defect is the difference in the mass of an atom and the sum of the masses of all of the particles (electrons, protons, and neutrons) of which it is composed. This mass defect occurs because matter is converted into energy according to the Einstein equation; this energy binds the nucleus together and overcomes the mutual repulsion between protons. In mass spectrometry, the mass defect is the term also used for the difference (whether positive or negative) between the exact mass of an ion, and the nearest integer mass.
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MeCAT is a proteomics quantification technology using metal coded tags (lanthanides) for marking biomolecules without the
necessity of isotopic labeling. After that they are analysed with
state-of-the-art mass spectrometric methods including ICP-MS with its
extraordinary advantages in quantification.
ICP-MS (inductively coupled plasma mass spectrometry) allows an ultra sensitive (absolute) quantification of the metals (lanthanides) tagged to proteins on protein level. Thus the protein amount can be accurately determinated down to low attomol range which is at least 2 to 3 orders of magnitude more sensitive than other mass spec (peptide based) techniques.
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Microwave-induced plasma consists of a quartz tube surrounded by a
microwave wave guide or cavity. Microwaves produced from a magnetron (a
microwave generator) fill the wave guide or cavity and cause the
electrons in the plasma support gas to oscillate. The oscillating
electrons collide with other atoms in the flowing gas to create and
maintain a high-temperature plasma. Typically 2.45 GHz, the same frequency as used in microwave ovens (l ~ 1.22 cm) is used for plasma generation. The MIP is typically used as a source for atomic emission spectrometry (MIP-AES) or mass Spectrometry (MIP-MS).
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Membrane inlet mass spectrometry (MIMS)
A membrane inlet system consists of a semipermeable membrane that permits passage of gas-phase volatile sample molecules directly into the mass spectrometer ion source, which is usually operated as an electron ionization or chemical ionization source.
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Native mass spectrometry (native MS) is defined as the process whereby
large biomolecules and complexes thereof can be transferred from a
three-dimensional, functional existence in a condensed liquid phase to
the gas phase via the process of electrospray ionization mass
spectrometry (ESI-MS). The experimental conditions where this is
possible are so mild that non-covalent interactions, the native state
and the associated biological action and functionality of the
molecule/complex are largely preserved.
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The ORS is a a type of collision/reaction cell used in inductively coupled plasma mass spectrometry to remove interfering ions through ion/neutral reactions. As the name implies, the cell is using a octople instead of a quadruple. The octopole reaction system (ORS)) uses only helium or hydrogen and the
volume of the cell is smaller than that of a DRC. The small molecules
of helium and hydrogen collide with the large, unwanted polyatomic ions
formed in the plasma and break them up into other ions that can be
separated in the quadrupole mass analyser. However, unlike the DRC the
OCR system is based only on collision reactions and not on chemical
reactions.
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A particle beam interface (PB) is a method for coupling liquid
chromatography to mass spectrometry in which the effluent is passed
through a heated capillary to form an expansion of vapor and aerosol
particles.
After passing through a skimmer, the beam impinges on a heated surface
to form ions through chemical ionization at the surface or ionization of
the resulting vapor in a CI or EI source.
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MS:
In QIT mass spectrometry when automatic
gain control is active a prescan preceeds every analytical scan to
determine the proper analytical ion injection time. It consists of a
short (<10 ms) ion injection to determine the ion current.
AES:
In atomic emission spectrometry with CCD/CID detection systems with limited linear working range a prescan preceeds every analytical measurement to determine the proper exposure time for every channel in order to stay within the upper electron capacity of the detector element.
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In a pyrolysis source interfaced with a mass spectrometer, the sample is thermally decomposed in a reproducible pyrolysis. The gaseous products formed are then analyzed either as a mixture by mass spectrometry, or are analyzed by GC/MS. Pyrolysis mass spectrometry can be used for the analysis of otherwise nonvolatile samples.
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In mass spectrometry relative intensity designates the ratio between the intensity of the ion beam for a certain mass and the maximum intensity of the ion beam. Normally this ratio is expressed using the heights of each peak on a spectrum with the highest peak defined as 100. Another method defines the total ion quantity or the ion quantity in a specific region as 100. The peak height method is also called the pattern coefficient while the ion quantity method is called the %? method. With the ion peak intensity terms for ion quantity (abundance), ion peak strength (intensity), peak height (height) and peak surface area (area) are also used.
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Selected reaction monitoring (SRM) is used to describe a mode of data
acquisition in tandem mass spectrometry where precursor and product ions
are selected in the first and second stages of mass spectrometry,
respectively
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Shotgun proteomics is a method of identifying proteins using a
combination of high performance liquid chromatography and mass
spectrometry in which the proteins in the mixture are digested and the
resulting peptides are separated by liquid chromatography and identified
by tandem mass spectrometry.
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Secondary ion mass spectrometry (SIMS) is a mass-spectrometric technique that is used for microscopic
chemical analysis. A beam of primary ions with an energy of 5- 20
kiloelectronvolts (keV) bombards a small spot on the surface of the
sample under ultra- high vacuum conditions. Positive and negative
secondary ions sputtered from the surface are analyzed in a mass
spectrometer in regards to their mass-to-charge ratio.
 EVISA Instrument Database: SIMS systems
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Optical spectrometry:
In optical spectrometry, the source of the spectrometer is the device from which the radiation is emitted. This may be a flame or plasma source.
Mass spectrometry:
The source is the device within the mass spectrometer in which ionization of sample molecules occurs. The source may be under vacuum, or it can operate at atmospheric pressure. A chromatographic method may interface with the source, or samples may be introduced via a probe or an automated sample introduction system. Ions are accelerated out of the source into the mass analyzer of the instrument.
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Transient
plasma triggered by imposing so high a voltage across a small gap
between conducting electrodes that the intervening gas ionizes.Spark devices are used as sources both for atomiuc emission spectrometry (Spark-OES) as well as mass spectrometry (SS-MS),
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Spark source mass spectrometry is a technique using a mass spectrometer with a spark ionization source.
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SIMS method featuring primary ion current densities (corresponding to SIMS gun flux) of 2 ~ 3 nA/cm2 or less and primarily used in analysis of sample surface components. The method is therefore distin-guished from dynamic SIMS, which is used for analysis of components in the depth direction. When the sample is an organic molecule in solid form, the term is changed to organic SIMS or molecular SIMS.
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Analytical efforts aiming on structural identification of molecules.
The techniques that have been developed for the identification of
chemical structures include mass spectrometry (MS), nuclear magnetic
resonance spectroscopy (NMR), infrared/ultraviolet spectrometry
(IR/UV), X-ray diffraction (XRD) and X-ray absorption fine structure
(XAFS) spectroscopy.
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Tandem Mass Spectrometry, usually referred to as MS/MS, involves the use of 2 or more mass analyzers. It is often used to analyze individual components in a mixture. This technique adds specificity to a given analysis.
The basic idea of MS/MS is a selection of a m/z of a given ion formed in the ion source, and subject this ion to fragmentation, usually by collision with inert gas (eg. Argon). The product ions are then detected. This is a powerful way of confirming the identity of certain compounds and determining the structure of unknown species. So MS/MS is a process that involves 3 steps: ionization-mass selection-mass analysis.
MS/MS could be performed on instruments such as triple quadrupole (QQQ), ion trap, time of flight, fourier transform, etc... The triple quadrupole is the most frequently used mass spectrometer for MS/MS, perhaps because of the cost and ease of use among other factors.
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The tandem MS is an instrumental arrangement in which ions
are subjected to two or more sequential stages (which may be separated
spatially or temporally) of analysis according to the mass-to-charge
ratio. The study of ions by means of two stages of mass analysis is
termed mass spectrometry/mass spectrometry (MS/MS)
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Top-down proteomics is a method of protein identification that uses the m/z selection of intact proteins followed by fragmentation and m/z separation in a second stage of mass spectrometry. Mixtures of proteins must first be separated by liquid chromatography or other separation method prior to mass spectrometry.
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An ion source for mass spectrometry capable of producing either
elemental or molecular information depending on the plasma power
selected.
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