Vet. World, 2012, Vol.5(3): 185-192 REVIEW Mass spectrometry- A review

The mass spectrometer is an instrument that can measure the masses and relative concentrations of atoms and molecules. It is also an analytical technique that identifies the chemical composition of a compound or sample based on the mass-to-charge ratio of charged particles. A mass spectrometer has three essential modules, an ion source-which transforms the molecules in a sample into ionized fragments, a mass analyser-which sorts the ions by their masses by applying electro- magnetic field and a detector-which measures the value of some indicator quantity and thus provides data for calculating the abundances each ion fragment present The technique has both qualitative and quantitative uses. Mass spectrometers are sensitive detectors of isotopes based on their masses. They are used in carbon dating and other radioactive dating processes. The combination of a mass spectrometer and a gas chromatograph makes a powerful tool for the detection of trace quantities of contaminants or toxins. A number of satellites and spacecraft have mass spectrometers for the identification of the small numbers of particles intercepted in space Mass spectrometry is an important tool for characterization of proteins. Pharmacokinetics is often studied using mass spectrometry because of the complex nature of the matrix (often blood or urine. Mass spectrometers are used for the analysis of residual gases in high vacuum systems.


Introduction
This is often important in determining the neutral mass but it also indicates something about Mass spectrometry (MS) is an analytical the nature of the molecules.Different types of ion technique that measures the mass-to-charge ratio source result in different arrays of fragments of charged particles (Sparkman, 2000).It is used produced from the original molecules.An electron for determining masses of particles, for determining ionization source produces many fragments and the elemental composition of a sample or molecule, mostly single-charged (1-) radicals (odd number and for elucidating the chemical structures of of electrons), whereas an electrospray source usually molecules, such as peptides and other chemical produces non-radical quasimolecular ions that compounds.The MS principle consists of ionizing are frequently multiply charged.Tandem mass chemical compounds to generate charged molecules spectrometry purposely produces fragment ions or molecule fragments and measuring their masspost-source and can drastically change the sort of to-charge ratios.Mass spectrometry data analysis data achieved by an experiment.In 1886, Eugen is a complicated subject that is very specific to the Goldstein observed rays in gas discharges under type of experiment producing the data.There are low pressure that travelled away from the anode general subdivisions of data that are fundamental and through channels in a perforated cathode, to understanding any data.Many mass spectrometers opposite to the direction of negatively charged work in either negative ion mode or positive ion cathode rays (which travel from cathode to mode.It is very important to know whether the anode).Goldstein called these positively charged observed ions are negatively or positively charged.anode rays "Kanalstrahlen"; the standard translation by mass spectrometry.Electron ionization and chemical ionization are used for gases and vapors. of this term into English is "canal rays".Wilhelm In chemical ionization sources, the analyte is Wien found that strong electric or magnetic fields ionized by chemical ion-molecule reactions deflected the canal rays and, in 1899, constructed during collisions in the source.Two techniques a device with parallel electric and magnetic fields often used with liquid and solid biological that separated the positive rays according to their samples include electrospray ionization (Feen et charge-to-mass ratio (Q/m).Wien found that the al., 1989) and matrix-assisted laser desorption/ charge-to-mass ratio depended on the nature of ionization (MALDI, initially developed as a the gas in the discharge tube.English scientist J.J. similar technique "Soft Laser Desorption (SLD)" Thomson later improved on the work of Wien by (Tanaka et al., 1988) (SIMS), spark ionization and thermal ionization (TIMS) (Bruins et al., 1991).* An ion source, which can convert gas phase sample molecules into ions (or, in the case of Analyzer electrospray ionization, move ions that exist There are many types of mass analyzers, using in solution into the gas phase) either static or dynamic fields, and magnetic or * A mass analyzer, which sorts the ions by electric fields, but all operate according to the their masses by applying electromagnetic above differential equation.Each analyzer type fields has its strengths and weaknesses.Many mass * A detector, which measures the value of an spectrometers use two or more mass analyzers for indicator quantity and thus provides data for tandem mass spectrometry (MS/MS).In addition calculating the abundances of each ion to the more common mass analyzers listed below, present.
there are others designed for special situations.

The technique has both qualitative and
There are several important analysers' quantitative uses.These include identifying unknown characteristics.The mass resolving power is the compounds, determining the isotopic composition measure of the ability to distinguish two peaks of of elements in a molecule, and determining the slightly different m/z.The mass accuracy is the structure of a compound by observing its fragratio of the m/z measurement error to the true m/z mentation.Other uses include quantifying the usually measured in ppm or milli mass units.The amount of a compound in a sample or studying mass range is the range of m/z amenable to the fundamentals of gas phase ion chemistry (the analysis by a given analyzer.The linear dynamic chemistry of ions and neutrals in a vacuum).MS range is the range over which ion signal is linear is now in very common use in analytical laboratories with analyte concentration.Speed refers to the that study physical, chemical, or biological properties time frame of the experiment and ultimately is of a great variety of compounds.
used to determine the number of spectra per unit

Ion source
time that can be generated.The ion source is the part of the mass Sector instruments spectrometer that ionizes the material under analysis (the analyte).The ions are then transported A sector field mass analyzer uses an electric by magnetic or electric fields to the mass analyzer.
and/or magnetic field to affect the path and/or Techniques for ionization have been key to velocity of the charged particles in some way.As shown above, sector instruments bend the determining what types of samples can be analyzed trajectories of the ions as they pass through the ejected.Ions are trapped in a mainly quadrupole mass analyzer, according to their mass-to-charge RF field, in a space defined by a ring electrode ratios, deflecting the more charged and faster-(usually connected to the main RF potential) moving, lighter ions more.The analyzer can be between two endcap electrodes (typically used to select a narrow range of m/z or to scan connected to DC or auxiliary AC potentials).The through a range of m/z to catalog the ions present sample is ionized either internally (e.g. with an (Cottrell and Greathead, 1986).
electron or laser beam), or externally, in which case the ions are often introduced through an Time-of-flight: The time-of-flight (TOF) aperture in an endcap electrode.Ions may also be analyzer uses an electric field to accelerate the ejected by the resonance excitation method, ions through the same potential, and then whereby a supplemental oscillatory excitation measures the time they take to reach the detector.voltage is applied to the endcap electrodes, and If the particles all have the same charge, the the trapping voltage amplitude and/or excitation kinetic energies will be identical, and their voltage frequency is varied to bring ions into a velocities will depend only on their masses.resonance condition in order of their mass/charge Lighter ions will reach the detector first (Wollnik, ratio (March, 2000).The cylindrical ion trap mass 1993).
spectrometer is a derivative of the quadrupole ion Quadrupole mass filter: Quadrupole mass trap mass spectrometer.analyzers use oscillating electrical fields to A linear quadrupole ion trap is similar to a quadrupole ion trap, but it traps ions in a two selectively stabilize or destabilize the paths of dimensional quadrupole field, instead of a three-ions passing through a radio frequency (RF) quadrupole field created between 4 parallel rods.dimensional quadrupole field as in a 3D Only the ions in a certain range of mass/charge quadrupole ion trap.Thermo Fisher's LTQ ratio are passed through the system at any time, ("linear trap quadrupole") is an example of the but changes to the potentials on the rods allow a linear ion trap (Schwartz et al., 2002).wide range of m/z values to be swept rapidly, A toroidal ion trap can be visualized as a either continuously or in a succession of discrete linear quadrupole curved around and connected hops.A quadrupole mass analyzer acts as a massat the ends or as a cross section of a 3D ion trap selective filter and is closely related to the rotated on edge to form the toroid, donut shaped quadrupole ion trap, particularly the linear trap.The trap can store large volumes of ions by quadrupole ion trap except that it is designed to distributing them throughout the ring-like trap pass the untrapped ions rather than collect the structure.Additionally all ions are stored in the trapped ones, and is for that reason referred to as a same trapping field and ejected together transmission quadrupole.A common variation of simplifying detection that can be complicated the quadrupole is the triple quadrupole.Triple with array configurations due to variations in quadrupole mass spectrometers have three detector alignment and machining of the arrays consecutive quadrupoles arranged in series to (Lammert et al., 2006).incoming ions.The first quadrupole acts as a Fourier transform ion cyclotron resonance: mass filter.The second quadrupole acts as a Fourier transform mass spectrometry (FTMS), or collision cell where selected ions are broken into more precisely Fourier transform ion cyclotron fragments.The resulting fragments can once resonance MS, measures mass by detecting the again be filtered by the third quadrupole or all be image current produced by ions cyclotroning in allowed to pass though to the detector yielding an the presence of a magnetic field.Instead of ms/ms fragmentation pattern.
measuring the deflection of ions with a detector such as an electron multiplier, the ions are Ion traps: The quadrupole ion trap works on the injected into a Penning trap (a static electric/ same physical principles as the quadrupole mass magnetic ion trap) where they effectively form analyzer, but the ions are trapped and sequentially part of a circuit.Detectors at fixed positions in separated by some form of molecule space measure the electrical signal of ions which fragmentation.For example, one mass analyzer pass near them over time, producing a periodic can isolate one peptide from many entering a mass spectrometer.A second mass analyzer then signal.Since the frequency of an ion's cycling is stabilizes the peptide ions while they collide with determined by its mass to charge ratio, this can be a gas, causing them to fragment by collisiondeconvoluted by performing a Fourier transform induced dissociation (CID).A third mass analyzer on the signal.FTMS has the advantage of high then sorts the fragments produced from the sensitivity (since each ion is "counted" more than peptides.Tandem MS can also be done in a single once) and much higher resolution and thus mass analyzer over time, as in a quadrupole ion precision.(Marshall et al., 1998).Ion cyclotron trap.There are various methods for fragmenting resonance (ICR) is an older mass analysis molecules for tandem MS, including collisiontechnique similar to FTMS except that ions are induced dissociation (CID), electron capture detected with a traditional detector.Ions trapped dissociation (ECD), electron transfer dissociation in a Penning trap are excited by an RF electric (ETD), infrared multiphoton dissociation (IRMPD), field until they impact the wall of the trap, where blackbody infrared radiative dissociation (BIRD), the detector is located.Ions of different mass are electron-detachment dissociation (EDD) and resolved according to impact time.
surface-induced dissociation (SID).An important Detectors application using tandem mass spectrometry is in protein identification.Chromatographic techniques The final element of the mass spectrometer combined with mass spectrometry.An important is the detector.The detector records either the enhancement to the mass resolving and mass charge induced or the current produced when an determining capabilities of mass spectrometry is ion passes by or hits a surface.In a scanning using it in tandem with chromatographic instrument, the signal produced in the detector separation techniques.during the course of the scan versus where the instrument is in the scan (at what m/Q) will GC -Mass Spectrometry produce a mass spectrum, a record of ions as a A common combination is gas chromatofunction of m/Q.Typically, some type of electron graphy-mass spectrometry (GC/MS or GC-MS).multiplier is used, though other detectors In this technique, a gas chromatograph is used to including Faraday cups and ion-to-photon separate different compounds.This stream of detectors are also used.Because the number of separated compounds is fed online into the ion ions leaving the mass analyzer at a particular source, a metallic filament to which voltage is instant is typically quite small, considerable applied.This filament emits electrons which amplification is often necessary to get a signal.ionize the compounds.The ions can then further Microchannel plate detectors are commonly used fragment, yielding predictable patterns.Intact in modern commercial instruments (Dubois et al., ions and fragments pass into the mass spectro-1999).In FTMS and Orbitraps, the detector meter's analyzer and are eventually detected consists of a pair of metal surfaces within the (Eiceman, 2000).mass analyzer/ion trap region which the ions only pass near as they oscillate.No DC current is LC-Mass Spectrometry produced, only a weak AC image current is Liquid chromatography mass spectrometry produced in a circuit between the electrodes.
(LC/MS or LC-MS) separates compounds chro-Other inductive detectors have also been used matographically before they are introduced to the ( Park et al., 1994).
ion source and mass spectrometer.It differs from

Tandem mass spectrometry
GC/MS in that the mobile phase is liquid, usually a mixture of water and organic solvents, instead A tandem mass spectrometer is one capable of gas and the ions fragments cannot yield ped of multiple rounds of mass spectrometry, usually predictable patterns.Most commonly, an electro-analyses.Results can also depend heavily on how spray ionization source is used in LC/MS.There the sample was prepared and how it was run/ are also some newly developed ionization techniques introduced.An important example is the issue of like laser spray.
which matrix is used for MALDI spotting, since much of the energetics of the desorption/ Ion mobility ionization event is controlled by the matrix rather Ion mobility spectrometry/mass spectrometry than the laser power.Sometimes samples are (IMS/MS or IMMS) is a technique where ions are spiked with sodium or another ion-carrying first separated by drift time through some neutral species to produce adducts rather than a gas under an applied electrical potential gradient protonated species.before being introduced into a mass spectrometer.
The greatest source of trouble when non-Drift time is a measure of the radius relative to the mass spectrometrists try to conduct mass spectrocharge of the ion.The duty cycle of IMS (the time metry on their own or collaborate with a mass over which the experiment takes place) is longer spectrometrist is inadequate definition of the than most mass spectrometric techniques, such research goal of the experiment.Adequate definition that the mass spectrometer can sample along the of the experimental goal is a prerequisite for course of the IMS separation.This produces data collecting the proper data and successfully about the IMS separation and the mass-to-charge interpreting it.Among the determinations that ratio of the ions in a manner similar to LC/MS can be achieved with mass spectrometry are (Matz et al., 2002).The duty cycle of IMS is short molecular mass, molecular structure, and sample relative to liquid chromatography or gas chromapurity.Each of these questions requires a different tography separations and can thus be coupled to experimental procedure.Simply asking for a such techniques, producing triple modalities such "mass spec" will most likely not answer the real as LC/IMS/MS.question at hand.

Data and analysis Interpretation of mass spectra
Mass spectrometry produces various types Since the precise structure or peptide sequence of data.The most common data representation is of a molecule is deciphered through the set of the mass spectrum.Certain types of mass spectrofragment masses, the interpretation of mass metry data are best represented as a mass spectra requires combined use of various techniques.chromatogram.Types of chromatograms include Usually the first strategy for identifying an unknown selected ion monitoring (SIM), total ion current compound is to compare its experimental mass spectrum against a library of mass spectra.If the (TIC), and selected reaction monitoring chrosearch comes up empty, then manual interpretation matogram (SRM), among many others.Other (Turecek et al., 1993) or software assisted types of mass spectrometry data are well represented interpretation of mass spectra are performed.as a three-dimensional contour map.In this form, Computer simulation of ionization and fragmentation the mass-to-charge, m/z is on the x-axis, intensity the y-axis, and an additional experimental processes occurring in mass spectrometer is the parameter, such as time, is recorded on the z-axis.primary tool for assigning structure or peptide By understanding the origin of a sample, certain sequence to a molecule.An a priori structural expectations can be assumed as to the component information is fragmented in silico and the molecules of the sample and their fragmentations.resulting pattern is compared with observed spectrum.Such simulation is often supported by a A sample from a synthesis/manufacturing process fragmentation library (Mistrik, 2004) that contains will probably contain impurities chemically published patterns of known decomposition related to the target component.A relatively reactions.Software taking advantage of this idea crudely prepared biological sample will probably has been developed for both small molecules and contain a certain amount of salt, which may form proteins.adducts with the analyte molecules in certain Another way of interpreting mass spectra (PTR-MS), are variants of chemical ionization dedicated for trace gas analysis of air, breath or involves spectra with accurate mass.A mass-tocharge ratio value (m/z) with only integer liquid headspace using well defined reaction time precision can represent an immense number of allowing calculations of analyte concentrations theoretically possible ion structures.More from the known reaction kinetics without the precise mass figures significantly reduce the need for internal standard or calibration.number of candidate molecular formulas, albeit 3. Pharmacokinetics-Pharmacokinetics is often each can still represent large number of studied using mass spectrometry because of the structurally diverse compounds.A computer complex nature of the matrix (often blood or algorithm called formula generator calculates all urine) and the need for high sensitivity to observe molecular formulas that theoretically fit a given low dose and long time point data.The most mass with specified tolerance.common instrumentation used in this application A recent technique for structure elucidation is LC-MS with a triple quadrupole mass spectrometer.in mass spectrometry, called precursor ion Tandem mass spectrometry is usually employed fingerprinting identifies individual pieces of for added specificity.Standard curves and structural information by conducting a search of internal standards are used for quantitation of the tandem spectra of the molecule under investiusually a single pharmaceutical in the samples.gation against a library of the product-ion spectra There is currently considerable interest in the use of structurally characterized precursor ions.
of very high sensitivity mass spectrometry for

Applications of Mass spectrometry
micro dosing studies, which are seen as a promising alternative to animal experimentation.1. Isotope ratio mass spectrometry-Mass spectrometry is used to determine the isotopic 4. Protein characterization-Mass spectrometry composition of elements within a sample.is an important emerging method for the Differences in mass among isotopes of an characterization and sequencing of proteins.The element are very small, and the less abundant two primary methods for ionization of whole isotopes of an element are typically very rare, so a proteins are electrospray ionization (ESI) and very sensitive instrument is required.These matrix-assisted laser desorption/ionization instruments, sometimes referred to as isotope (MALDI).In keeping with the performance and ratio mass spectrometers (IR-MS), usually use a mass range of available mass spectrometers, two single magnet to bend a beam of ionized particles approaches are used for characterizing proteins.towards a series of Faraday cups which convert In the first, intact proteins are ionized by either of particle impacts to electric current.A fast on-line the two techniques described above, and then analysis of deuterium content of water can be introduced to a mass analyzer.This approach is done using flowing afterglow mass spectrometry, referred to as "top-down" strategy of protein FA-MS.Probably the most sensitive and accurate analysis.In the second, proteins are enzymatically mass spectrometer for this purpose is the digested into smaller peptides using proteases accelerator mass spectrometer (AMS).Isotope such as trypsin or pepsin, either in solution or in ratios are important markers of a variety of gel after electrophoretic separation.Other processes.Some isotope ratios are used to proteolytic agents are also used.The collection of determine the age of materials for example as in peptide products are then introduced to the mass carbon dating.Labeling with stable isotopes is analyzer.also used for protein quantification.
5. Space exploration-Mass spectrometers are 2. Trace gas analysis-Several techniques use also widely used in space missions to measure the ions created in a dedicated ion source injected composition of plasmas.For example, the into a flow tube or a drift tube: selected ion flow Cassini spacecraft carries the Cassini Plasma tube (SIFT-MS), and proton transfer reaction Spectrometer (CAPS), which measures the mass