Mass spectrometry , also called mass spectroscopy , analytic technique by which chemical substances are identified by the sorting of gaseous ions in electric and magnetic fields according to their mass-to-charge ratios. The instruments used in such studies are called mass spectrometers and mass spectrographs , and they operate on the principle that moving ions may be deflected by electric and magnetic fields. The two instruments differ only in the way in which the sorted charged particles are detected. In the mass spectrometer they are detected electrically, in the mass spectrograph by photographic or other nonelectrical means; the term mass spectroscope is used to include both kinds of devices. Since electrical detectors are now most commonly used, the field is typically referred to as mass spectrometry.
The foundation of mass spectroscopy was laid inwhen Wilhelm Wiena German physicist, discovered that beams of charged particles could be deflected by a magnetic field. In more refined experiments carried out between an the British physicist J. Thomsonwho had already discovered the electron and observed its deflection by an electric fiel passed a beam of positively charged ions through a combined electrostatic and magnetic field.
The net result was that the ions produced a series of parabolic curves on a photographic plate placed in their paths. Each parabola corresponded to ions of a particular mass-to-charge ratio with the specific position of each ion dependent on its velocity; the lengths of the parabolic curves provided a measure of the range of ion energies contained in the beam.
Later, in an attempt to estimate the relative abundances of the various ion species present, Thomson replaced the photographic plate with a metal sheet in which was cut a parabolic slit. By varying the magnetic field, he was able to scan through a mass spectrum and measure a current corresponding to each separated ion species. Thus he may be credited with the construction of the first mass spectrograph and the first mass spectrometer.
The most noteworthy observation made with the parabola spectrography was the spectrum of rare gases present in the atmosphere. In addition to lines due to helium mass 4neon mass 20and argon mass 40there was a line corresponding to an ion of mass 22 that could not be attributed to any known gas.
The existence of forms of the same element with different masses had been suspected since it had been found that many pairs of radioactive materials could not be separated by chemical means.
The ion of mass 22 was, in fact, a stable heavy isotope of neon. The spectroscopes discussed so far are analogous to the pinhole camera in optics, because no focusing of the ion beams is involved. The introduction of focusing types of mass spectroscopes came in the years and was due to the British chemist and physicist Francis W. Aston and to the American physicist Arthur J. He chose 16 O the isotope of oxygen of mass 16 as his standard of mass. This spectrometer was employed by Dempster to make accurate determinations of the abundances of the isotopes of magnesium, lithium, potassium, calcium, and zinc, laying the foundation for similar measurements of the isotopes of all the elements.
The resolving power, or resolutionof a mass spectroscope is a measure of its ability to separate adjacent masses that are displayed as peaks on the detector.
The early machines had resolving powers of only a few hundred. In an Dempster, Kenneth T. Bainbridge, both working in the United States, and Josef Mattauchin Germany, independently developed instruments with electric and magnetic fields arranged in tandem in such a way that ion beams that emerged from the source slits in divergent directions and with different velocities were refocused.
Hard ionization techniques are processes which impart high quantities of residual energy in the subject molecule invoking large degrees of fragmentation i.
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. Inductively coupled plasma 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 can be used in experiments which seek to use mass spectrometry as a means of resolving chemical kinetics mechanisms and isomeric product branching.
Some applications for ambient ionization include environmental applications as well as clinical applications.
In these techniques, ions form in an ion source outside the mass spectrometer. Sampling becomes easy as the samples don't need previous separation nor preparation. Mass analyzers separate the ions according to their mass-to-charge ratio. The following two laws govern the dynamics of charged particles in electric and magnetic fields in vacuum:. This differential equation is the classic equation of motion for charged particles. Thus mass spectrometers could be thought of as "mass-to-charge spectrometers".
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.
In addition to the more common mass analyzers listed below, there are others designed for special situations. There are several important analyser characteristics.
Mass accuracy is usually measured in ppm or milli mass units. The linear dynamic range is the range over which ion signal is linear with analyte concentration.
Another recent analytical advance in zircon dating is the application of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) coupled to a laser system. The laser produces a beam of ions focused on a spot as small as 10 microns in diameter, which during the analysis produces a pit of between 2 and 1, microns deep. Accelerator mass spectrometry (AMS) is a form of mass spectrometry that accelerates ions to extraordinarily high kinetic energies before mass analysis. The special strength of AMS among the mass spectrometric methods is its power to separate a rare isotope from an abundant neighboring mass ("abundance sensitivity", e.g. 14 C from 12 C). The method suppresses Analytes: Organic molecules, Biomolecules. Before accelerator mass spectrometry (AMS) dating, obtaining reliable radiocarbon dates from bulk sediments was also problematic. Palynology was the main tool of early studies, but stable isotope analysis has produced the most detailed lake-based records for this region.
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. As shown above, sector instruments 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 time-of-flight TOF analyzer uses an electric field to accelerate the ions through the same potentialand then measures the time they take to reach the detector.
If the particles all have the same chargetheir kinetic energies will be identical, and their velocities will depend only on their masses. Ions with a lower mass will reach the detector first.
The initial velocity is often not dependent on the mass of the ion TOF-MS, and will turn into a difference in the final velocity. Quadrupole mass analyzers use oscillating electrical fields to selectively stabilize or destabilize the paths of ions passing through a radio frequency RF quadrupole field created between 4 parallel rods. A quadrupole mass analyzer acts as a mass-selective filter and is closely related to the quadrupole ion trapparticularly 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. 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.
Radiocarbon Dating using Mass Spectometry
Likewise, a triple quad can be made to perform various scan types characteristic of tandem mass spectrometry. The quadrupole ion trap 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. There are also non-destructive analysis methods. The cylindrical ion trap mass spectrometer 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. A linear quadrupole ion trap 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.
Accelerator Mass Spectrometry Advantages. The greatest advantage that AMS radiocarbon dating has over radiometric methods is small sample size. Accelerator mass spectrometers need only as little as 20 milligrams and as high as milligrams for certain samples whereas conventional methods need at least 10 grams in samples like wood and charcoal and as much . The advent of accelerator mass spectrometry (AMS) 14 C dating of small ( mg) samples of foraminifera allowed many of the world's deep-sea and shelf sediments to be directly dated up to a limit of between 30 and 40 years ago. Because of the small sample size required and the relatively fast turnaround, it became possible to. Mass Spectrometry - Essays and Tutorials © JEOL USA, Inc.!"#$ be peaks at mass 14 and 15 in the mass spectrum of ammonia corresponding to a N+ and [NH]+ (nitrogen is atomic mass 14). A trained mass spectrometrist can interpret the masses and.
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. Orbitrap instruments are similar to Fourier transform ion cyclotron resonance mass spectrometers see text below.
Ions are electrostatically 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 image current 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 Fourier transformation of the recorded image currents. Orbitraps have a high mass accuracy, high sensitivity and a good dynamic range. Fourier transform mass spectrometry FTMSor more precisely Fourier transform ion cyclotron resonance MS, measures mass by detecting the image current produced by ions cyclotroning in the presence of a magnetic field.
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 deconvoluted by performing a Fourier transform on the signal.
FTMS has the advantage of high sensitivity since each ion is "counted" more than once and much higher resolution and thus precision. Ion cyclotron resonance ICR is an older mass analysis technique similar to FTMS except that ions are detected with a traditional detector. Ions trapped in a Penning trap 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. 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.
Typically, some type of electron multiplier is used, though other detectors including Faraday cups and ion-to-photon detectors 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.
Microchannel plate detectors are commonly used in modern commercial instruments. 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. A tandem mass spectrometer 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 peptide 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 collision-induced dissociation 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 quadrupole ion trap. An important application using tandem mass spectrometry is in protein identification.
Tandem mass spectrometry enables a variety of experimental sequences. Many commercial mass spectrometers are designed to expedite the execution of such routine sequences as selected reaction monitoring SRM 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 duty cycle 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. This experiment is used to detect specific motifs within unknown molecules. Another type of tandem mass spectrometry used for radiocarbon dating is accelerator mass spectrometry AMSwhich uses very high voltages, usually in the mega-volt range, to accelerate negative ions into a type of tandem mass spectrometer.
When a specific combination of source, analyzer, and detector becomes conventional in practice, a compound acronym may arise to designate it succinctly. 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 isotope ratio mass spectrometry IRMSwhich 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.
An important enhancement to the mass resolving and mass determining capabilities of mass spectrometry is using it in tandem with chromatographic and other separation techniques.
In this technique, a gas chromatograph is used to separate different compounds. This stream of separated compounds is fed online into the ion source, a metallic filament to which voltage 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. It differs from GC-MS in that the mobile phase is liquid, usually a mixture of water and organic solventsinstead of gas. Most commonly, an electrospray ionization source is used in LC-MS. Other popular and commercially available LC-MS ion sources are atmospheric pressure chemical ionization and atmospheric pressure photoionization.
There are also some newly developed ionization techniques like laser spray. Capillary electrophoresis-mass spectrometry CE-MS is a technique that combines the liquid separation process of capillary electrophoresis with mass spectrometry.
Mass spectrometry (MS) is an analytical technique that measures the mass-to-charge ratio of jankossencontemporary.com results are typically presented as a mass spectrum, a plot of intensity as a function of the mass-to-charge jankossencontemporary.com spectrometry is used in many different fields and is applied to pure samples as well as complex mixtures. The mass of these ions is then measured by the application of magnetic and electric fields. The measurement of radiocarbon by mass spectrometry is very difficult because its concentration is less than one atom in 1, The accelerator is used to help remove ions that might be confused with radiocarbon before the final detection. Mar 24, Mass spectrometry, also called mass spectroscopy, analytic technique by which chemical substances are identified by the sorting of gaseous ions in electric and magnetic fields according to their mass-to-charge jankossencontemporary.com instruments used in such studies are called mass spectrometers and mass spectrographs, and they operate on the principle that moving ions .
The duty cycle 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. Mass spectrometry produces various types of data. The most common data representation is the mass spectrum. Certain types of mass spectrometry data are best represented as a mass chromatogram. Other types of mass spectrometry data are well represented as a three-dimensional contour map.
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 electronswhereas an electrospray source usually produces non-radical quasimolecular ions that are frequently multiply charged.
Radiocarbon dating, also known as carbon dating, is a radioactive decay-based method for determining the age of organic remains that lived within the past 50, years. Most carbon is created from nitrogen in the earth's upper atmosphere as a consequence of cosmic ray bombardment. It is one of several similarly formed cosmogenic nuclides.
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 crudely prepared biological sample will probably contain a certain amount of salt, which may form adducts with the analyte molecules in certain analyses. 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.
Since the precise structure or peptide sequence of a molecule is deciphered through the set of fragment masses, the interpretation of mass spectra 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 software assisted interpretation of mass spectra must be performed.
Computer simulation of ionization and fragmentation processes occurring in mass spectrometer is the primary tool for assigning structure or peptide sequence to a molecule. An a priori structural information is fragmented in silico 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. Software taking advantage of this idea has been developed for both small molecules and proteins. Analysis of mass spectra can also be spectra with accurate mass.
A computer algorithm called formula generator calculates all molecular formulas that theoretically fit a given mass with specified tolerance. A recent technique for structure elucidation in mass spectrometry, called precursor ion fingerprintingidentifies individual pieces of structural information by conducting a search of the tandem spectra of the molecule under investigation against a library of the product-ion spectra of structurally characterized precursor ions.
Mass spectrometry has both qualitative and quantitative uses. These include identifying unknown compounds, determining the isotopic composition of elements in a molecule, and determining the structure of a compound by observing its fragmentation. Other uses include quantifying the amount of a compound in a sample or studying the fundamentals of gas phase ion chemistry 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. Mass spectrometry is also used to determine the isotopic 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-MSusually use a single magnet to bend a beam of ionized particles towards a series of Faraday cups which convert particle impacts to electric current.
A fast on-line analysis of deuterium content of water can be done using flowing afterglow mass spectrometryFA-MS. Probably the most sensitive and accurate mass spectrometer for this purpose is the accelerator mass spectrometer AMS.
Some isotope ratios are used to determine the age of materials for example as in carbon dating. Labeling with stable isotopes is also used for protein quantification. This method allows the study of gases as they evolve in solution.
This method has been extensively used for the study of the production of oxygen by Photosystem II. Several techniques use ions created in a dedicated ion source injected into a flow tube or a drift tube: selected ion flow tube SIFT-MSand proton transfer reaction PTR-MSare variants of chemical ionization 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.
Mass spectrometry dating
Another technique with applications in trace gas analysis field is secondary electrospray ionization SESI-MSwhich is a variant of electrospray ionization.
SESI consist of an electrospray plume of pure acidified solvent that interacts with neutral vapors. Vapor molecules get ionized at atmospheric pressure when charge is transferred from the ions formed in the electrospray to the molecules. An atom probe is an instrument that combines time-of-flight mass spectrometry and field-evaporation microscopy to map the location of individual atoms. 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 LC-MS with a triple quadrupole mass spectrometer. 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.
Much attention is paid to the linearity of the standard curve; however it is not uncommon to use curve fitting 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 microdosing studies, which are seen as a promising alternative to animal experimentation. Recent studies show that secondary electrospray ionization SESI is a powerful technique to monitor drug kinetics via breath analysis.
This allows for the number of collected data-points to be greatly increased. Mass spectrometry is an important method for the characterization and sequencing of proteins. 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 " top-down " 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 peptides using proteases such as trypsin or pepsineither in solution or in gel after electrophoretic separation.
Other proteolytic agents are also used. The collection of peptide products are often separated by chromatography prior to introduction to the mass analyzer.
When the characteristic pattern of peptides is used for the identification of the protein the method is called peptide mass fingerprinting PMFif the identification is performed using the sequence data determined in tandem MS analysis it is called de novo peptide sequencing.
These procedures of protein analysis are also referred to as the " bottom-up " approach, and have also been used to analyse the distribution and position of post-translational modifications such as phosphorylation on proteins. As a standard method for analysis, mass spectrometers have reached other planets and moons.
Two were taken to Mars by the Viking program. In early the Cassini-Huygens mission delivered a specialized GC-MS instrument aboard the Huygens probe through the atmosphere of Titanthe largest moon of the planet Saturn. 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. Mass spectrometers are also widely used in space missions to measure the composition of plasmas.
Mass spectrometers were used in hospitals for respiratory gas analysis beginning around through the end of the century. Some are probably still in use but none are currently being manufactured. Found mostly in the operating roomthey were a part of a complex system, in which respired gas samples from patients undergoing anesthesia 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 ufragmentation of some of the heavier molecules negated the need for a higher detection limit. 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.