Electrospray (nanoSpray) ionization source

Electrospray ionization (ESI) is a technique used in mass spectrometry to produce ions. It is especially useful in producing ions from macromolecules because it overcomes the propensity of these molecules to fragment when ionized. The development of electrospray ionization for the analysis of biological macromolecules^[1] was rewarded with the attribution of the Nobel Prize in Chemistry to John Bennett Fenn in 2002.^[2] Image File history File linksMetadata No higher resolution available. ... Image File history File linksMetadata No higher resolution available. ... Mass spectrometry (also known as mass spectroscopy (deprecated)[1] or informally, mass-spec and MS) is an analytical technique used to measure the mass-to-charge ratio of ions. ... A macromolecule is a molecule composed of a very large number of atoms. ... This is a list of Nobel Prize laureates in Chemistry from 1901 to 2006. ... Dr. John B. Fenn Dr. John Bennett Fenn (born June 15, 1917 in New York City) is a research professor of analytical chemistry who was awarded the Nobel Prize in Chemistry in 2002. ... For album titles with the same name, see 2002 (album). ...

How it works

In electrospray ionization, a liquid is pushed through a very small, charged and usually metal, capillary.^[3] This liquid contains the substance to be studied, the analyte, dissolved in a large amount of solvent, which is usually much more volatile than the analyte. Volatile acids, bases or buffers are often added to this solution too. The analyte exists as an ion in solution either in a protonated form or as an anion. Because like charges repel, the liquid pushes itself out of the capillary and forms an aerosol, a mist of small droplets about 10 μm across. The aerosol is at least partially produced by a process involving the formation of a Taylor cone and a jet from the tip of this cone. An uncharged carrier gas such as nitrogen is sometimes used to help nebulize the liquid and to help evaporate the neutral solvent in the droplets. As the solvent evaporates, the analyte molecules are forced closer together, repel each other and break up the droplets. This process is called Coulombic fission because it is driven by repulsive Coulombic forces between charged molecules. The process repeats until the analyte is free of solvent and is a lone ion. There is still debate about the exact mechanism of the process, particularly the last stage, when lone ions form. Lone ions move to the mass analyzer of a mass spectrometer. Ionization is the physical process of converting an atom or molecule into an ion by changing the difference between the number of protons and electrons. ... A liquid will usually assume the shape of its container A liquid is one of the main states of matter. ... Hot metal work from a blacksmith In chemistry, a metal (Greek: Metallon) is an element that readily loses electrons to form positive ions (cations) and has metallic bonds between metal atoms. ... This article does not cite any references or sources. ... An Analyte is the substance or chemical constituent that is undergoing analysis. ... A solvent is a liquid that dissolves a solid, liquid, or gaseous solute, resulting in a solution. ... The ability of a liquid to evaporate quickly and at relatively low temperatures. ... Acidity redirects here. ... Acids and bases: Acid-base reaction pH Self-ionization of water Buffer solutions Systematic naming Acid-base extraction Acidity function Proton affinity Acids: Strong acids Weak acids Superacids Lewis acids Mineral acids Organic acids Bases: Strong bases Weak bases Superbases Lewis bases Organic bases edit In chemistry, a base is... Buffer solutions are solutions which resist change in pH upon addition of small amounts of acid or base. ... An electrostatic potential map of the nitrate ion (NO3−). Areas coloured red are lower in energy than areas colored yellow An ion is an atom or group of atoms which have lost or gained one or more electrons, making them negatively or positively charged. ... Protonation is the addition of a proton (H+) to an atom, molecule, or ion. ... An anion is an ion with negative charge. ... Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ... Particulates, alternatively referred to as particulate matter (PM), aerosols or fine particles, are tiny particles of solid or liquid suspended in a gas. ... Look up micro- in Wiktionary, the free dictionary. ... A Taylor cone refers to the cone observed in electrospray and hydrodynamic spray processes from which a jet of charged particles emanates above a threshold voltage. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... A nebulizer with an attached inhaling apparatus In medicine, a nebulizer is a device used to administer medication to people in forms of a liquid mist to the airways. ... Evaporation is the process whereby atoms or molecules in a liquid state (or solid state if the substance sublimes) gain sufficient energy to enter the gaseous state. ... In physics, Coulombs law is an inverse-square law indicating the magnitude and direction of electrical force that one stationary, electrically charged substance of small volume (ideally, a point source) exerts on another. ... An electrostatic potential map of the nitrate ion (NO3−). Areas coloured red are lower in energy than areas colored yellow An ion is an atom or group of atoms which have lost or gained one or more electrons, making them negatively or positively charged. ... Unsolved problems in physics: What causes anything to have mass? The U.S. National Prototype Kilogram, which currently serves as the primary standard for measuring mass in the U.S. Mass is the property of a physical object that quantifies the amount of matter and energy it is equivalent to. ... Mass spectrometry is a technique for separating ions by their mass-to-charge (m/z) ratios. ...

In electrospray processes, the ions observed may be quasimolecular ions created by the addition of a proton (a hydrogen ion) and denoted , or of another cation such as sodium ion, , or the removal of a proton, . Multiply-charged ions such as are often observed. For large macromolecules, there can be many charge states, occurring with different frequencies; the charge can be as great as , for example. All these are even-electron ion species: electrons (alone) are not added or removed, unlike in some other ionizations. The formation of ions in electrospray is somewhat homologous to acid-base reactions. Redox reactions do occur and a circuit with measurable current flow exists, but atomic and molecular ions are the primary carriers of charge in the solution and gas phases. In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ... A cation is an ion with positive charge. ... General Name, Symbol, Number sodium, Na, 11 Chemical series alkali metals Group, Period, Block 1, 3, s Appearance silvery white Standard atomic weight 22. ... A macromolecule is a molecule composed of a very large number of atoms. ... e- redirects here. ... Illustration of a redox reaction Redox (shorthand for oxidation/reduction reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. ...

History

Early researchers:

• Rayleigh
• Zeleny^[4]
• Gall^[5]
• Dole^[6]

John William Strutt, 3rd Baron Rayleigh (12 November 1842 – 30 June 1919) was an English physicist who (with William Ramsay) discovered the element argon, an achievement that earned him the Nobel Prize for Physics in 1904. ...

Ionization mechanism

There are two major competing theories about the final production of lone ions, the charged residue model (CRM) and the ion evaporation model (IEM). ^[7]

Electrospray droplets start off highly charged, and as they shrink through evaporation the Coulomb repulsion forces approach the force of surface tension that holds droplet together. The droplet then becomes unstable and disintegrates into several droplets of smaller radius. In physics, surface tension is an effect within the surface layer of a liquid that causes that layer to behave as an elastic sheet. ...

The Charged Residue Model suggests that electrospray droplets undergo evaporation and disintegration cycles, with each initial droplet leading to a multitude of much smaller "daughter" droplets. Each final "daughter" droplet contains on average one or less molecule of analyte. When the last solvent molecules evaporate from such droplet the analyte molecule is left with the charges that the droplet carried.

The Ion Evaporation (Desorption) Model suggests that as the droplet reaches a certain radius the field strength at the surface of the droplet becomes great enough to push or desorb ions directly out of the droplet. Characteristically, the fission event corresponds to an almost negligible loss in droplet mass, but a significant drop in charge.

It has been suggested that both models probably occur for different analytes/solvents and in the limit of both models they have a tendency to converge. That is to say that the distinction between a droplet containing an analyte molecule and an analyte molecule surrounded by a layer of solvent eventually disappears and coulombic fission looks a lot like ion evaporation. The real question is scale and timing and the techniques to definitively determine this are not yet available.

The use of the word "ionization" in "electrospray ionization" is criticized by some because many of the ions observed are thought to be preformed in solution before the electrospray process or created by simple changes in concentrations as the aerosolized droplets shrink. It is argued that electrospray is simply an interface for transferring ions from the solution phase to the gas phase. Dissolving table salt (NaCl) in water This article is about a chemical solution; for other uses of the term solution, see solution (disambiguation). ... This article does not cite any references or sources. ...

Variants

There are many variations on the basic electrospray technique, that generally offer better sensitivity than it.^[8] Two important ones are microspray (µ-spray) and nanospray.^[9] The primary difference is in the reduced flow rate of the analyte containing liquid, µLiters/minute and nLiters/minute respectively; this causes many other differences, such as the reduced internal diameter of the tubing or lack of nebulization gas.

Applications

Liquid chromatography–mass spectrometry

see also the main article on liquid chromatography-mass spectrometry

Electrospray ionization is the primary ion source used in liquid chromatography-mass spectrometry because it is a liquid-gas interface capable of coupling liquid chomatography with mass spectrometry. Liquid chromatography-mass spectrometry (LC-MS)is an analytical chemistry technique that combines the physical separation capabilities of liquid chromatography (aka HPLC) with the mass analysis capabilities of mass spectrometry. ... Liquid chromatography-mass spectrometry (LC-MS)is an analytical chemistry technique that combines the physical separation capabilities of liquid chromatography (aka HPLC) with the mass analysis capabilities of mass spectrometry. ... Chromatography is a family of analytical chemistry techniques for the separation of mixtures. ... Mass spectrometry (also known as mass spectroscopy (deprecated)[1] or informally, mass-spec and MS) is an analytical technique used to measure the mass-to-charge ratio of ions. ...

Noncovalent gas phase interactions

Electrospray ionization is also ideal in studying noncovalent gas phase interactions. The electrospray process is capable of transferring liquid-phase noncovalent complexes into the gas phase without disrupting the noncovalent interaction. This means that a cluster of two molecules can be studied in the gas phase by other mass spectrometry techniques. An interesting example of this is studying the interactions between enzymes and drugs which are inhibitors of the enzyme. Because inhibitors generally work by noncovalently binding to its target enzyme with reasonable affinity the noncovalent complex can be studied in this way. Competition studies have been done in this way to screen for potential new drug candidates. Noncovalent bonding refers to a variety of interactions, that are not covalent in nature, between molecules or parts of molecules that provide force to hold the molecules or parts of molecules together usually in a specific orientation or conformation. ... Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ...

Colloid thrusters

Electrospray techniques are used to control satellites, since the fine-controllable particle ejection allows precise and effective thrusts.^[10] 20 μN colloid thruster system[1] A colloid thruster is a type of ion thruster which uses electrostatic acceleration of charged liquid droplets for propulsion. ... An Earth observation satellite, ERS 2 For other uses, see Satellite (disambiguation). ...

Deposition of particles for nanostructures

Electrospray may be used in nanotechnology, to deposit single particles on surfaces.^[11] This is done by spraying colloids on average containing only one particle per droplet. The solvent evaporates, leaving an aerosol stream of single particles of the desired type. The ionizing property of the process is not crucial for the application but may be used in electrostatic precipitation of the particles. Buckminsterfullerene C60, also known as the buckyball, is the simplest of the carbon structures known as fullerenes. ... A colloid or colloidal dispersion, is a form of matter intermediate between a true solution and a mixture (suspension). ... Aerosol, is a term derived from the fact that matter floating in air is a suspension (a mixture in which solid or liquid or combined solid-liquid particles are suspended in a fluid). ... An electrostatic precipitator (ESP), or electrostatic air cleaner is a particulate collection device that removes particles from a flowing gas (such as air) using the force of an induced electrostatic charge. ...

References

Science is the journal of the American Association for the Advancement of Science (AAAS). ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Mass Spectrometry Reviews (usually abbreviated as ), is a peer-reviewed scientific journal, published since 1982 by John Wiley & Sons. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Physical Review is one of the oldest and most-respected scientific journals publishing research on all aspects of physics. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... The Journal of Chemical Physics is a scientific journal that publishes research papers on all areas of chemical physics. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ...

See also

• Taylor cone

A Taylor cone refers to the cone observed in electrospray and hydrodynamic spray processes from which a jet of charged particles emanates above a threshold voltage. ...

External links

• A thesis with significant background on electrospray ionization
• New Objective: What is Electrospray?