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Determination of na and k by flame photometer


Orbitrap mass spectrometer

Mass spectrometry (MS) is an analytical technique that ionizes and sorts the based on their . In simpler terms, a 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.

A mass spectrum is a plot of the ion signal as a function of the mass-to-charge ratio. These spectra are used to determine the elemental or of a sample, the masses of particles and of , and to elucidate the chemical structures of and other .

In a typical MS procedure, a sample, which may be solid, liquid, or gas, is ionized, for example by bombarding it with electrons. This may cause some of the sample's molecules to break into charged fragments. These ions are then separated according to their mass-to-charge ratio, typically by accelerating them and subjecting them to an electric or magnetic field: ions of the same mass-to-charge ratio will undergo the same amount of deflection. The ions are detected by a mechanism capable of detecting charged particles, such as an . Results are displayed as spectra of the relative abundance of detected ions as a function of the mass-to-charge ratio. The atoms or molecules in the sample can be identified by correlating known masses (e.g. an entire molecule) to the identified masses or through a characteristic fragmentation pattern.

Contents

History[]

Further information:

Replica of 's third mass spectrometer

In 1886, observed rays in under low pressure that traveled away from the and through channels in a perforated , opposite to the direction of negatively charged (which travel from cathode to anode). Goldstein called these positively charged "Kanalstrahlen"; the standard translation of this term into English is "". found that strong electric or magnetic fields deflected the canal rays and, in 1899, constructed a device with perpendicular electric and magnetic fields that separated the positive rays according to their charge-to-mass ratio (Q/m). Wien found that the charge-to-mass ratio depended on the nature of the gas in the discharge tube. English scientist later improved on the work of Wien by reducing the pressure to create the mass spectrograph.

Calutron mass spectrometers were used in the for uranium enrichment.

The word spectrograph had become part of the by 1884. Early spectrometry devices that measured the mass-to-charge ratio of ions were called which consisted of instruments that recorded a of mass values on a . A mass spectroscope is similar to a mass spectrograph except that the beam of ions is directed onto a screen. A mass spectroscope configuration was used in early instruments when it was desired that the effects of adjustments be quickly observed. Once the instrument was properly adjusted, a photographic plate was inserted and exposed. The term mass spectroscope continued to be used even though the direct illumination of a phosphor screen was replaced by indirect measurements with an . The use of the term mass spectroscopy is now discouraged due to the possibility of confusion with light . Mass spectrometry is often abbreviated as mass-spec or simply as MS.

Modern techniques of mass spectrometry were devised by and in 1918 and 1919 respectively.

known as were developed by and used for separating the during the . Calutron mass spectrometers were used for at the established during World War II.

In 1989, half of the was awarded to and for the development of the ion trap technique in the 1950s and 1960s.

In 2002, the was awarded to for the development of (ESI) and for the development of (SLD) and their application to the ionization of biological macromolecules, especially proteins.

Parts of a mass spectrometer[]

Schematics of a simple mass spectrometer with sector type mass analyzer. This one is for the measurement of carbon dioxide ratios () as in the

A mass spectrometer consists of three components: an ion source, a mass analyzer, and a detector. The converts a portion of the sample into ions. There is a wide variety of ionization techniques, depending on the phase (solid, liquid, gas) of the sample and the efficiency of various ionization mechanisms for the unknown species. An extraction system removes ions from the sample, which are then targeted through the mass analyzer and into the detector. The differences in masses of the fragments allows the mass analyzer to sort the ions by their mass-to-charge ratio. The detector measures the value of an indicator quantity and thus provides data for calculating the abundances of each ion present. Some detectors also give spatial information, e.g., a multichannel plate.

Theoretical example[]

The following example describes the operation of a spectrometer mass analyzer, which is of the type. (Other analyzer types are treated below.) Consider a sample of (table salt). In the ion source, the sample is (turned into ) and ionized (transformed into electrically charged particles) into (Na+) and (Cl−) ions. Sodium atoms and ions are , with a mass of about 23 u. Chloride atoms and ions come in two isotopes with masses of approximately 35 u (at a natural abundance of about 75 percent) and approximately 37 u (at a natural abundance of about 25 percent). The analyzer part of the spectrometer contains and fields, which exert forces on ions traveling through these fields. The speed of a charged particle may be increased or decreased while passing through the electric field, and its direction may be altered by the magnetic field. The magnitude of the deflection of the moving ion's trajectory depends on its mass-to-charge ratio. Lighter ions get deflected by the magnetic force more than heavier ions (based on , F = ma). The streams of sorted ions pass from the analyzer to the detector, which records the relative abundance of each ion type. This information is used to determine the chemical element composition of the original sample (i.e. that both sodium and chlorine are present in the sample) and the isotopic composition of its constituents (the ratio of 35Cl to 37Cl).

Creating ions[]

The is the part of the mass spectrometer that ionizes the material under analysis (the analyte). The ions are then transported by or to the mass analyzer.

Techniques for ionization have been key to determining what types of samples can be analyzed by mass spectrometry. and are used for and . In chemical ionization sources, the analyte is ionized by chemical ion-molecule reactions during collisions in the source. Two techniques often used with and biological samples include (invented by ) and (MALDI, initially developed as a similar technique "Soft Laser Desorption (SLD)" by K. Tanaka for which a Nobel Prize was awarded and as MALDI by M. Karas and F. Hillenkamp).

Hard ionization and soft ionization[]

Quadrupole mass spectrometer and electrospray ion source used for Fenn's early work

In mass spectrometry, ionization refers to the production of gas phase ions suitable for resolution in the mass analyser or mass filter. Ionization occurs in the . There are several available; each has advantages and disadvantages for particular applications. For example, (EI) gives a high degree of fragmentation, yielding highly detailed mass spectra which when skilfully analysed can provide important information for structural elucidation/characterisation and facilitate identification of unknown compounds by comparison to mass spectral libraries obtained under identical operating conditions. However, EI is not suitable for coupling to , i.e. , since at atmospheric pressure, the filaments used to generate electrons burn out rapidly. Thus EI is coupled predominantly with , i.e. , where the entire system is under high vacuum.

Hard ionization techniques are processes which impart high quantities of residual energy in the subject molecule invoking large degrees of fragmentation (i.e. the systematic rupturing of bonds acts to remove the excess energy, restoring stability to the resulting ion). Resultant ions tend to have m/z lower than the molecular mass (other than in the case of proton transfer and not including isotope peaks). The most common example of hard ionization is electron ionization (EI).

Soft ionization refers to the processes which impart little residual energy onto the subject molecule and as such result in little fragmentation. Examples include (FAB), (CI), (APCI), (ESI), and (MALDI).

Inductively coupled plasma[]

Inductively coupled plasma ion source

(ICP) sources are used primarily for cation analysis of a wide array of sample types. In this source, a plasma that is electrically neutral overall, but that has had a substantial fraction of its atoms ionized by high temperature, is used to atomize introduced sample molecules and to further strip the outer electrons from those atoms. The plasma is usually generated from argon gas, since the first ionization energy of argon atoms is higher than the first of any other elements except He, O, F and Ne, but lower than the second ionization energy of all except the most electropositive metals. The heating is achieved by a radio-frequency current passed through a coil surrounding the plasma.

Photoionization mass spectrometry[]

can be used in experiments which seek to use mass spectrometry as a means of resolving chemical kinetics mechanisms and isomeric product branching. In such instances a high energy photon, either X-ray or uv, is used to dissociate stable gaseous molecules in a carrier gas of He or Ar. In instances where a light source is utilzed, a tuneable photon energy can be utilized to acquire a photoionization efficiency curve which can be used in conjunction with the charge ratio m/z to fingerprint molecular and ionic species.

Other ionization techniques[]

Others include , (FD), (FAB), , (DIOS), (DART), (APCI), (SIMS), and (TIMS).

Mass selection[]

Mass analyzers separate the ions according to their . The following two laws govern the dynamics of charged particles in electric and magnetic fields in vacuum:

F = Q ( E + v × B ) {\displaystyle \mathbf {F} =Q(\mathbf {E} +\mathbf {v} \times \mathbf {B} )} \mathbf{F} = Q (\mathbf{E} + \mathbf{v} \times \mathbf{B}) (); F = m a {\displaystyle \mathbf {F} =m\mathbf {a} } \mathbf {F} =m\mathbf {a} ( of motion in non-relativistic case, i.e. valid only at ion velocity much lower than the speed of light).

Here F is the force applied to the ion, m is the mass of the ion, a is the acceleration, Q is the ion charge, E is the electric field, and v × B is the of the ion velocity and the magnetic field

Equating the above expressions for the force applied to the ion yields:

( m / Q ) a = E + v × B . {\displaystyle (m/Q)\mathbf {a} =\mathbf {E} +\mathbf {v} \times \mathbf {B} .} (m/Q)\mathbf{a} = \mathbf{E}+ \mathbf{v} \times \mathbf{B}.

This is the classic equation of motion for . Together with the particle's initial conditions, it completely determines the particle's motion in space and time in terms of m/Q. Thus mass spectrometers could be thought of as "mass-to-charge spectrometers". When presenting data, it is common to use the (officially) m/z, where z is the number of (e) on the ion (z=Q/e). This quantity, although it is informally called the mass-to-charge ratio, more accurately speaking represents the ratio of the mass number and the charge number, z.

There are many types of mass analyzers, using either static or dynamic fields, and magnetic or electric fields, but all operate according to the above differential equation. Each analyzer type has its strengths and weaknesses. Many mass spectrometers use two or more mass analyzers for . In addition to the more common mass analyzers listed below, there are others designed for special situations.

There are several important analyser characteristics. The is the measure of the ability to distinguish two peaks of slightly different m/z. The mass accuracy is the ratio of the m/z measurement error to the true m/z. Mass accuracy is usually measured in or . The mass range is the range of m/z amenable to analysis by a given analyzer. The linear dynamic range is the range over which ion signal is linear with analyte concentration. Speed refers to the time frame of the experiment and ultimately is used to determine the number of spectra per unit time that can be generated.

Sector instruments[]

ThermoQuest AvantGarde sector mass spectrometer

Further information:

A sector field mass analyzer uses a static electric and/or magnetic field to affect the path and/or of the particles in some way. As shown above, bend the trajectories of the ions as they pass through the mass analyzer, according to their mass-to-charge ratios, deflecting the more charged and faster-moving, lighter ions more. The analyzer can be used to select a narrow range of m/z or to scan through a range of m/z to catalog the ions present.

Time-of-flight[]

Further information:

The (TOF) analyzer uses an to accelerate the ions through the same , and then measures the time they take to reach the detector. If the particles all have the same , the tends to be identical, and their , in this case, will depend only on their . Ions with a lower mass will reach the detector first. However, in reality, even particles with the same m/z can arrive at different times at the detector, because they have different initial velocities. The initial velocity is not dependent on the mass of the ion what becomes a problem for the TOF-MS. The difference in initial velocity turns into difference in the final velocity. In this way, ions with the same m/z are going to arrive at different times in the detector. For fixing this problem, time-lag focusing/ has been coupled with TOF-MS.

Quadrupole mass filter[]

Further information:

use oscillating electrical fields to selectively stabilize or destabilize the paths of ions passing through a (RF) field created between 4 parallel rods. Only the ions in a certain range of mass/charge ratio are passed through the system at any time, but changes to the potentials on the rods allow a wide range of m/z values to be swept rapidly, either continuously or in a succession of discrete hops. A quadrupole mass analyzer acts as a mass-selective filter and is closely related to the , particularly the linear quadrupole ion trap except that it is designed to pass the untrapped ions rather than collect the trapped ones, and is for that reason referred to as a transmission quadrupole. A magnetically enhanced quadrupole mass analyzer includes the addition of a magnetic field, either applied axially or transversely. This novel type of instrument leads to an additional performance enhancement in terms of resolution and/or sensitivity depending upon the magnitude and orientation of the applied magnetic field. A common variation of the transmission quadrupole is the triple quadrupole mass spectrometer. The “triple quad” has three consecutive quadrupole stages, the first acting as a mass filter to transmit a particular incoming ion to the second quadrupole, a collision chamber, wherein that ion can be broken into fragments. The third quadrupole also acts as a mass filter, to transmit a particular fragment ion to the detector. If a quadrupole is made to rapidly and repetitively cycle through a range of mass filter settings, full spectra can be reported. Likewise, a triple quad can be made to perform various scan types characteristic of .

Ion traps[]

Three-dimensional quadrupole ion trap[]

Further information:

The works on the same physical principles as the quadrupole mass analyzer, but the ions are trapped and sequentially ejected. Ions are trapped in a mainly quadrupole RF field, in a space defined by a ring electrode (usually connected to the main RF potential) between two endcap electrodes (typically connected to DC or auxiliary AC potentials). The sample is ionized either internally (e.g. with an electron or laser beam), or externally, in which case the ions are often introduced through an aperture in an endcap electrode.

There are many mass/charge separation and isolation methods but the most commonly used is the mass instability mode in which the RF potential is ramped so that the orbit of ions with a mass a > b are stable while ions with mass b become unstable and are ejected on the z-axis onto a detector. There are also non-destructive analysis methods.

Ions may also be ejected by the resonance excitation method, whereby a supplemental oscillatory excitation voltage is applied to the endcap electrodes, and the trapping voltage amplitude and/or excitation voltage frequency is varied to bring ions into a resonance condition in order of their mass/charge ratio.

Cylindrical ion trap[]

The (CIT) is a derivative of the quadrupole ion trap where the electrodes are formed from flat rings rather than hyperbolic shaped electrodes. The architecture lends itself well to miniaturization because as the size of a trap is reduced, the shape of the electric field near the center of the trap, the region where the ions are trapped, forms a shape similar to that of a hyperbolic trap.

Linear quadrupole ion trap[]

A is similar to a quadrupole ion trap, but it traps ions in a two dimensional quadrupole field, instead of a three-dimensional quadrupole field as in a 3D quadrupole ion trap. Thermo Fisher's LTQ ("linear trap quadrupole") is an example of the linear ion trap.

A toroidal ion trap can be visualized as a linear quadrupole curved around and connected at the ends or as a cross section of a 3D ion trap rotated on edge to form the toroid, donut shaped trap. The trap can store large volumes of ions by distributing them throughout the ring-like trap structure. This toroidal shaped trap is a configuration that allows the increased miniaturization of an ion trap mass analyzer. Additionally all ions are stored in the same trapping field and ejected together simplifying detection that can be complicated with array configurations due to variations in detector alignment and machining of the arrays.

As with the toroidal trap, linear traps and 3D quadrupole ion traps are the most commonly miniaturized mass analyzers due to their high sensitivity, tolerance for mTorr pressure, and capabilities for single analyzer tandem mass spectrometry (e.g. product ion scans).

Orbitrap[]

Orbitrap mass analyzer

Further information:

instruments are similar to mass spectrometers (see text below). Ions are trapped in an orbit around a central, spindle shaped electrode. The electrode confines the ions so that they both orbit around the central electrode and oscillate back and forth along the central electrode's long axis. This oscillation generates an in the detector plates which is recorded by the instrument. The frequencies of these image currents depend on the mass-to-charge ratios of the ions. Mass spectra are obtained by of the recorded image currents.

Orbitraps have a high mass accuracy, high sensitivity and a good dynamic range.

Fourier transform ion cyclotron resonance[]

Fourier transform ion cyclotron resonance mass spectrometer

Further information:

(FTMS), or more precisely MS, measures mass by detecting the produced by ions in the presence of a magnetic field. Instead of measuring the deflection of ions with a detector such as an , the ions are injected into a (a static electric/magnetic ) where they effectively form part of a circuit. Detectors at fixed positions in space measure the electrical signal of ions which pass near them over time, producing a periodic signal. Since the frequency of an ion's cycling is determined by its mass-to-charge ratio, this can be by performing a on the signal. has the advantage of high sensitivity (since each ion is "counted" more than once) and much higher and thus precision.

(ICR) is an older mass analysis technique similar to FTMS except that ions are detected with a traditional detector. Ions trapped in a are excited by an RF electric field until they impact the wall of the trap, where the detector is located. Ions of different mass are resolved according to impact time.

Detectors[]

A continuous dynode particle multiplier detector

The final element of the mass spectrometer is the detector. The detector records either the charge induced or the current produced when an ion passes by or hits a surface. In a scanning instrument, the signal produced in the detector during the course of the scan versus where the instrument is in the scan (at what m/Q) will produce a , a record of ions as a function of m/Q.

Typically, some type of is used, though other detectors including and are also used. Because the number of ions leaving the mass analyzer at a particular instant is typically quite small, considerable amplification is often necessary to get a signal. are commonly used in modern commercial instruments. In and , the detector consists of a pair of metal surfaces within the mass analyzer/ion trap region which the ions only pass near as they oscillate. No direct current is produced, only a weak AC image current is produced in a circuit between the electrodes. Other inductive detectors have also been used.

Tandem mass spectrometry[]

Tandem mass spectrometry for biological molecules using ESI or

A is one capable of multiple rounds of mass spectrometry, usually separated by some form of molecule fragmentation. For example, one mass analyzer can isolate one from many entering a mass spectrometer. A second mass analyzer then stabilizes the peptide ions while they collide with a gas, causing them to fragment by (CID). A third mass analyzer then sorts the fragments produced from the peptides. Tandem MS can also be done in a single mass analyzer over time, as in a . There are various methods for molecules for tandem MS, including (CID), (ECD), (ETD), (IRMPD), (BIRD), (EDD) and (SID). An important application using tandem mass spectrometry is in .

Tandem mass spectrometry enables a variety of experimental sequences. Many commercial mass spectrometers are designed to expedite the execution of such routine sequences as and precursor ion scanning. In SRM, the first analyzer allows only a single mass through and the second analyzer monitors for multiple user-defined fragment ions. SRM is most often used with scanning instruments where the second mass analysis event is limited. These experiments are used to increase specificity of detection of known molecules, notably in pharmacokinetic studies. Precursor ion scanning refers to monitoring for a specific loss from the precursor ion. The first and second mass analyzers scan across the spectrum as partitioned by a user-defined m/z value. This experiment is used to detect specific motifs within unknown molecules.

Another type of tandem mass spectrometry used for is (AMS), which uses very high voltages, usually in the mega-volt range, to accelerate negative ions into a type of tandem mass spectrometer.

Common mass spectrometer configurations and techniques[]

When a specific combination of source, analyzer, and detector becomes conventional in practice, a compound may arise to designate it succinctly. One example is , which refers to a combination of a source with a mass analyzer. Other examples include , , and .

Certain applications of mass spectrometry have developed monikers that although strictly speaking would seem to refer to a broad application, in practice have come instead to connote a specific or a limited number of instrument configurations. An example of this is , which refers in practice to the use of a limited number of sector based mass analyzers; this name is used to refer to both the application and the instrument used for the application.

Separation techniques combined with mass spectrometry[]

An important enhancement to the mass resolving and mass determining capabilities of mass spectrometry is using it in tandem with and other separation techniques.

Gas chromatography[]

Main article:

A gas chromatograph (right) directly coupled to a mass spectrometer (left)

A common combination is chromatography-mass spectrometry (GC/MS or GC-MS). In this technique, a is used to separate different compounds. This stream of separated compounds is fed online into the source, a to which is applied. This filament emits electrons which ionize the compounds. The ions can then further fragment, yielding predictable patterns. Intact ions and fragments pass into the mass spectrometer's analyzer and are eventually detected.

Liquid chromatography[]

Main article:

Similar to gas chromatography MS (GC-MS), liquid chromatography-mass spectrometry (LC/MS or LC-MS) separates compounds chromatographically before they are introduced to the ion source and mass spectrometer. It differs from GC-MS in that the mobile phase is liquid, usually a mixture of and organic , instead of gas. Most commonly, an source is used in LC-MS. Other popular and commercially available LC-MS ion sources are and . There are also some newly developed ionization techniques like .

Capillary electrophoresis–mass spectrometry[]

Main article:

Capillary electrophoresis–mass spectrometry (CE-MS) is a technique that combines the liquid separation process of with mass spectrometry. CE-MS is typically coupled to electrospray ionization.

Ion mobility[]

Main article:

Ion mobility spectrometry-mass spectrometry (IMS/MS or IMMS) is a technique where ions are first separated by drift time through some neutral gas under an applied electrical potential gradient before being introduced into a mass spectrometer. Drift time is a measure of the radius relative to the charge of the ion. The of IMS (the time over which the experiment takes place) is longer than most mass spectrometric techniques, such that the mass spectrometer can sample along the course of the IMS separation. This produces data about the IMS separation and the mass-to-charge ratio of the ions in a manner similar to .

The duty cycle of IMS is short relative to liquid chromatography or gas chromatography separations and can thus be coupled to such techniques, producing triple modalities such as LC/IMS/MS.

Data and analysis[]

Mass spectrum of a peptide showing the isotopic distribution

Data representations[]

See also:

Mass spectrometry produces various types of data. The most common data representation is the .

Certain types of mass spectrometry data are best represented as a . Types of chromatograms include (SIM), (TIC), and (SRM), among many others.

Other types of mass spectrometry data are well represented as a three-dimensional . In this form, the mass-to-charge, m/z is on the x-axis, intensity the y-axis, and an additional experimental parameter, such as time, is recorded on the z-axis.

Data analysis[]

Mass spectrometry data analysis is specific to the type of experiment producing the data. General subdivisions of data are fundamental to understanding any data.

Many mass spectrometers work in either negative ion mode or positive ion mode. It is very important to know whether the observed ions are negatively or positively charged. This is often important in determining the neutral mass but it also indicates something about the nature of the molecules.

Different types of ion source result in different arrays of fragments produced from the original molecules. An electron ionization source produces many fragments and mostly single-charged (1-) radicals (odd number of electrons), whereas an electrospray source usually produces non-radical quasimolecular ions that are frequently multiply charged. Tandem mass spectrometry purposely produces fragment ions post-source and can drastically change the sort of data achieved by an experiment.

Knowledge of the origin of a sample can provide insight into the component molecules of the sample and their fragmentations. A sample from a synthesis/manufacturing process will probably contain impurities chemically related to the target component. A crudely prepared biological sample will probably contain a certain amount of salt, which may form with the analyte molecules in certain analyses.

Results can also depend heavily on sample preparation and how it was run/introduced. An important example is the issue of which matrix is used for MALDI spotting, since much of the energetics of the desorption/ionization event is controlled by the matrix rather than the laser power. Sometimes samples are spiked with sodium or another ion-carrying species to produce adducts rather than a protonated species.

Mass spectrometry can measure molar mass, molecular structure, and sample purity. Each of these questions requires a different experimental procedure; therefore, adequate definition of the experimental goal is a prerequisite for collecting the proper data and successfully interpreting it.

Interpretation of mass spectra[]

electron ionization mass spectrum

Main article:

Since the precise or of a molecule is deciphered through the set of fragment masses, the interpretation of requires combined use of various techniques. Usually the first strategy for identifying an unknown compound is to compare its experimental mass spectrum against a library of mass spectra. If no matches result from the search, then manual interpretation or must be performed. Computer simulation of and fragmentation processes occurring in mass spectrometer is the primary tool for assigning structure or peptide sequence to a molecule. An structural information is fragmented and the resulting pattern is compared with observed spectrum. Such simulation is often supported by a fragmentation library that contains published patterns of known decomposition reactions. taking advantage of this idea has been developed for both small molecules and .

Analysis of mass spectra can also be spectra with . A mass-to-charge ratio value (m/z) with only integer precision can represent an immense number of theoretically possible ion structures; however, more precise mass figures significantly reduce the number of candidate . A computer algorithm called formula generator calculates all molecular formulas that theoretically fit a given with specified tolerance.

A recent technique for structure elucidation in mass spectrometry, called , identifies individual pieces of structural information by conducting a search of the of the molecule under investigation against a library of the of structurally characterized precursor ions.

Applications[]

Mass spectrometry has both and uses. These include identifying unknown compounds, determining the composition of elements in a molecule, and determining the of a compound by observing its fragmentation. Other uses include quantifying the amount of a compound in a sample or studying the fundamentals of (the chemistry of ions and neutrals in a vacuum). MS is now commonly used in analytical laboratories that study physical, chemical, or biological properties of a great variety of compounds.

As an analytical technique it possesses distinct advantages such as: Increased sensitivity over most other analytical techniques because the analyzer, as a mass-charge filter, reduces background interference, Excellent specificity from characteristic fragmentation patterns to identify unknowns or confirm the presence of suspected compounds, Information about molecular weight, Information about the isotopic abundance of elements, Temporally resolved chemical data.

A few of the disadvantages of the method is that it often fails to distinguish between optical and geometrical isomers and the positions of substituent in o-, m- and p- positions in an aromatic ring. Also, its scope is limited in identifying hydrocarbons that produce similar fragmented ions.

Isotope ratio MS: isotope dating and tracing[]

Mass spectrometer to determine the 16O/18O and 12C/13C isotope ratio on biogenous carbonate

Main article:

Mass spectrometry is also used to determine the composition of elements within a sample. Differences in mass among isotopes of an element are very small, and the less abundant isotopes of an element are typically very rare, so a very sensitive instrument is required. These instruments, sometimes referred to as isotope ratio mass spectrometers (IR-MS), usually use a single magnet to bend a beam of ionized particles towards a series of which convert particle impacts to . A fast on-line analysis of content of water can be done using , FA-MS. Probably the most sensitive and accurate mass spectrometer for this purpose is the (AMS). This is because it provides ultimate sensitivity, capable of measuring individual atoms and measuring nuclides with a dynamic range of 1015 relative to the major stable isotope. Isotope ratios are important markers of a variety of processes. Some isotope ratios are used to determine the age of materials for example as in . Labeling with stable isotopes is also used for protein quantification. (see below)

Membrane-Inlet Mass Spectrometry: Measuring gasses in solution[]

, combines the Isotope ratio MS with a reaction chamber/cell separated by a gas-permeable membrane. This method allows the study of gasses as they evolve in solution. This method has been extensively used for the study of the production of oxygen by .

Trace gas analysis[]

Several techniques use ions created in a dedicated ion source injected into a flow tube or a drift tube: (SIFT-MS), and (PTR-MS), are variants of dedicated for trace gas analysis of air, breath or liquid headspace using well defined reaction time allowing calculations of analyte concentrations from the known reaction kinetics without the need for internal standard or calibration.

Atom probe[]

An is an instrument that combines mass spectrometry and field-evaporation microscopy to map the location of individual atoms.

Pharmacokinetics[]

Main article:

Pharmacokinetics is often studied using mass spectrometry because of the complex nature of the matrix (often blood or urine) and the need for high sensitivity to observe low dose and long time point data. The most common instrumentation used in this application is with a . Tandem mass spectrometry is usually employed for added specificity. Standard curves and internal standards are used for quantitation of usually a single pharmaceutical in the samples. The samples represent different time points as a pharmaceutical is administered and then metabolized or cleared from the body. Blank or t=0 samples taken before administration are important in determining background and ensuring data integrity with such complex sample matrices. Much attention is paid to the linearity of the standard curve; however it is not uncommon to use with more complex functions such as quadratics since the response of most mass spectrometers is less than linear across large concentration ranges.

There is currently considerable interest in the use of very high sensitivity mass spectrometry for studies, which are seen as a promising alternative to .

Protein characterization[]

Main article:

Mass spectrometry is an important method for the characterization and of proteins. The two primary methods for ionization of whole proteins are (ESI) and (MALDI). In keeping with the performance and mass range of available mass spectrometers, two approaches are used for characterizing proteins. In the first, intact proteins are ionized by either of the two techniques described above, and then introduced to a mass analyzer. This approach is referred to as "" strategy of protein analysis. The top-down approach however is largely limited to low-throughput single-protein studies. In the second, proteins are enzymatically digested into smaller using such as or , either in or after separation. Other proteolytic agents are also used. The collection of peptide products are then introduced to the mass analyzer. When the characteristic pattern of peptides is used for the identification of the protein the method is called (PMF), if the identification is performed using the sequence data determined in analysis it is called . These procedures of protein analysis are also referred to as the "" approach. A third approach however is beginning to be used, this intermediate "middle-down" approach involves analyzing proteolytic peptide larger than the typical tryptic peptide.

Glycan analysis[]

Mass spectrometry (MS), with its low sample requirement and high sensitivity, has been predominantly used in for characterization and elucidation of . Mass spectrometry provides a complementary method to for the analysis of glycans. Intact glycans may be detected directly as singly charged ions by (MALDI-MS) or, following permethylation or peracetylation, by (FAB-MS). (ESI-MS) also gives good signals for the smaller glycans. Various are now available which interpret MS data and aid in Glycan structure characterization.

Space exploration[]

NASA's analyzing a soil sample from the "Rosy Red" trench with the mass spectrometer

As a standard method for analysis, mass spectrometers have reached other planets and moons. Two were taken to by the . In early 2005 the mission delivered a specialized instrument aboard the through the atmosphere of , the largest moon of the planet . This instrument analyzed atmospheric samples along its descent trajectory and was able to vaporize and analyze samples of Titan's frozen, hydrocarbon covered surface once the probe had landed. These measurements compare the abundance of isotope(s) of each particle comparatively to earth's natural abundance. Also on board the spacecraft was an ion and neutral mass spectrometer which had been taking measurements of Titan's atmospheric composition as well as the composition of ' plumes. A mass spectrometer was carried by the launched in 2007.

Mass spectrometers are also widely used in space missions to measure the composition of plasmas. For example, the Cassini spacecraft carried the Cassini Plasma Spectrometer (CAPS), which measured the mass of ions in Saturn's .

Respired gas monitor[]

Mass spectrometers were used in hospitals for respiratory gas analysis beginning around 1975 through the end of the century. Some are probably still in use but none are currently being manufactured.

Found mostly in the , they were a part of a complex system, in which respired gas samples from patients undergoing were drawn into the instrument through a valve mechanism designed to sequentially connect up to 32 rooms to the mass spectrometer. A computer directed all operations of the system. The data collected from the mass spectrometer was delivered to the individual rooms for the anesthesiologist to use.

The uniqueness of this magnetic sector mass spectrometer may have been the fact that a plane of detectors, each purposely positioned to collect all of the ion species expected to be in the samples, allowed the instrument to simultaneously report all of the gases respired by the patient. Although the mass range was limited to slightly over 120 , fragmentation of some of the heavier molecules negated the need for a higher detection limit.

Preparative mass spectrometry[]

The primary function of mass spectrometry is as a tool for chemical analyses based on detection and quantification of ions according to their mass-to-charge ratio. However, mass spectrometry also shows promise for material synthesis. Ion soft landing is characterized by deposition of intact species on surfaces at low kinetic energies which precludes the fragmentation of the incident species. The soft landing technique was first reported in 1977 for the reaction of low energy sulfur containing ions on a lead surface.

See also[]

References[]

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  2. "[]." Merriam Webster. Accessed 13 June 2008.
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