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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 List of Glossaries)





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adduct ion
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

ambient mass spectrometry
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.  



AMS
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.

biological mass spectrometry
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.

chemical ionization (CI)
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.

collision reaction cell
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.

consecutive reaction monitoring
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.

continuous flow fast atom bombardment (CF-FAB)
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.

DART
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.

delayed extraction
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. 

desorption ionization (DI)
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.

dynamic secondary ion mass spectrometry (DSIMS)
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.

electron ionization (EI)
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.

electrospray ionization mass spectrometry (ESI MS)
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. 

elemental mass spectrometry
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.

fast atom bombardment mass spectrometry (FAB/MS)
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.

flow injection mass spectrometry (FI-MS)
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.

gas-chromatography mass spectrometry
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.

GC-ICP-MS
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.

glow discharge
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).

ICP-MS
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 1012. 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.
 
 

imaging mass spectrometry
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.

inductively coupled plasma
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).   
 

isotope fractionation (mass fractionation)
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.

isotope ratio mass spectrometry
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.

laser microprobe mass spectrometry (LMMS)
Laser desorption/ionization mass spectrometry, particularly emphasizing spatially resolved composition information.

(see also: LAMMA)

liquid chromatography mass spectrometry (LC-MS)
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.

MALDI
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.

mass defect
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. 

metal-coded affinity tag
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.

microwave-induced plasma (MIP)
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).

MIMS
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.

particle beam interface
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.

prescan
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.

Pyrolysis MS
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. 

relative intensity
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.

selected reaction monitoring
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

shotgun proteomics
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.

SIMS
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

source
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.

spark
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),

spark source mass spectrometry
Spark source mass spectrometry is a technique using a mass spectrometer with a spark ionization source.

static secondary ion mass spectrometry (SSIMS)
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.

structure analysis
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.

tandem mass spectrometry
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.


tandem MS
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)

top-down proteomics
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.

tunable plasma source
An ion source for mass spectrometry capable of producing either elemental or molecular information depending on the plasma power selected.










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