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Ionization is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule is called an ion. Ionization can result from the loss of an electron after collisions with subatomic particles, collisions with other atoms, molecules, electrons, positrons, protons, antiprotons and ions, or through the interaction with electromagnetic radiation. Heterolytic bond cleavage and heterolytic substitution reactions can result in the formation of ion pairs. Ionization can occur through radioactive decay by the internal conversion process, in which an excited nucleus transfers its energy to one of the inner-shell electrons causing it to be ejected.
Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a mass spectrum, a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is used in many different fields and is applied to pure samples as well as complex mixtures.
An ion source is a device that creates atomic and molecular ions. Ion sources are used to form ions for mass spectrometers, optical emission spectrometers, particle accelerators, ion implanters and ion engines.
Electron ionization is an ionization method in which energetic electrons interact with solid or gas phase atoms or molecules to produce ions. EI was one of the first ionization techniques developed for mass spectrometry. However, this method is still a popular ionization technique. This technique is considered a hard ionization method, since it uses highly energetic electrons to produce ions. This leads to extensive fragmentation, which can be helpful for structure determination of unknown compounds. EI is the most useful for organic compounds which have a molecular weight below 600 amu. Also, several other thermally stable and volatile compounds in solid, liquid and gas states can be detected with the use of this technique when coupled with various separation methods.
Tandem mass spectrometry, also known as MS/MS or MS2, is a technique in instrumental analysis where two or more stages of analysis using one or more mass analyzer are performed with an additional reaction step in between these analyses to increase their abilities to analyse chemical samples. A common use of tandem MS is the analysis of biomolecules, such as proteins and peptides.
Photoionization is the physical process in which an ion is formed from the interaction of a photon with an atom or molecule.
Fourier-transform ion cyclotron resonance mass spectrometry is a type of mass analyzer (or mass spectrometer) for determining the mass-to-charge ratio (m/z) of ions based on the cyclotron frequency of the ions in a fixed magnetic field. The ions are trapped in a Penning trap (a magnetic field with electric trapping plates), where they are excited (at their resonant cyclotron frequencies) to a larger cyclotron radius by an oscillating electric field orthogonal to the magnetic field. After the excitation field is removed, the ions are rotating at their cyclotron frequency in phase (as a "packet" of ions). These ions induce a charge (detected as an image current) on a pair of electrodes as the packets of ions pass close to them. The resulting signal is called a free induction decay (FID), transient or interferogram that consists of a superposition of sine waves. The useful signal is extracted from this data by performing a Fourier transform to give a mass spectrum.
Electron-capture dissociation (ECD) is a method of fragmenting gas-phase ions for structure elucidation of peptides and proteins in tandem mass spectrometry. It is one of the most widely used techniques for activation and dissociation of mass selected precursor ion in MS/MS. It involves the direct introduction of low-energy electrons to trapped gas-phase ions.
A triple quadrupole mass spectrometer (TQMS), is a tandem mass spectrometer consisting of two quadrupole mass analyzers in series, with a (non-mass-resolving) radio frequency (RF)–only quadrupole between them to act as a cell for collision-induced dissociation. This configuration is often abbreviated QqQ, here Q1q2Q3.
Instrumental analysis is a field of analytical chemistry that investigates analytes using scientific instruments.
In mass spectrometry, fragmentation is the dissociation of energetically unstable molecular ions formed from passing the molecules mass spectrum. These reactions are well documented over the decades and fragmentation patterns are useful to determine the molar weight and structural information of unknown molecules. Fragmentation that occurs in tandem mass spectrometry experiments has been a recent focus of research, because this data helps facilitate the identification of molecules.
Collision-induced dissociation (CID), also known as collisionally activated dissociation (CAD), is a mass spectrometry technique to induce fragmentation of selected ions in the gas phase. The selected ions are usually accelerated by applying an electrical potential to increase the ion kinetic energy and then allowed to collide with neutral molecules. In the collision, some of the kinetic energy is converted into internal energy which results in bond breakage and the fragmentation of the molecular ion into smaller fragments. These fragment ions can then be analyzed by tandem mass spectrometry.
Atmospheric pressure laser ionization is an atmospheric pressure ionization method for mass spectrometry (MS). Laser light in the UV range is used to ionize molecules in a resonance-enhanced multiphoton ionization (REMPI) process. It is a selective and sensitive ionization method for aromatic and polyaromatic compounds. Atmospheric photoionization is the latest in development of atmospheric ionization methods.
Photoelectron photoion coincidence spectroscopy (PEPICO) is a combination of photoionization mass spectrometry and photoelectron spectroscopy. It is largely based on the photoelectric effect. Free molecules from a gas-phase sample are ionized by incident vacuum ultraviolet (VUV) radiation. In the ensuing photoionization, a cation and a photoelectron are formed for each sample molecule. The mass of the photoion is determined by time-of-flight mass spectrometry, whereas, in current setups, photoelectrons are typically detected by velocity map imaging. Electron times-of-flight are three orders of magnitude smaller than those of ions, which allows electron detection to be used as a time stamp for the ionization event, starting the clock for the ion time-of-flight analysis. In contrast with pulsed experiments, such as REMPI, in which the light pulse must act as the time stamp, this allows to use continuous light sources, e.g. a discharge lamp or a synchrotron light source. No more than several ion–electron pairs are present simultaneously in the instrument, and the electron–ion pairs belonging to a single photoionization event can be identified and detected in delayed coincidence.
The magnesium argide ion, MgAr+ is an ion composed of one ionised magnesium atom, Mg+ and an argon atom. It is important in inductively coupled plasma mass spectrometry and in the study of the field around the magnesium ion. The ionization potential of magnesium is lower than the first excitation state of argon, so the positive charge in MgAr+ will reside on the magnesium atom. Neutral MgAr molecules can also exist in an excited state.
Infrared photodissociation (IRPD) spectroscopy uses infrared radiation to break bonds in, often ionic, molecules (photodissociation), within a mass spectrometer. In combination with post-ionization, this technique can also be used for neutral species. IRPD spectroscopy has been shown to use electron ionization, corona discharge, and electrospray ionization to obtain spectra of volatile and nonvolatile compounds. Ionized gases trapped in a mass spectrometer can be studied without the need of a solvent as in infrared spectroscopy.
Resonance ionization is a process in optical physics used to excite a specific atom beyond its ionization potential to form an ion using a beam of photons irradiated from a pulsed laser light. In resonance ionization, the absorption or emission properties of the emitted photons are not considered, rather only the resulting excited ions are mass-selected, detected and measured. Depending on the laser light source used, one electron can be removed from each atom so that resonance ionization produces an efficient selectivity in two ways: elemental selectivity in ionization and isotopic selectivity in measurement.
The triboracyclopropenyl fragment is a cyclic structural motif in boron chemistry, named for its geometric similarity to cyclopropene. In contrast to nonplanar borane clusters that exhibit higher coordination numbers at boron (e.g., through 3-center 2-electron bonds to bridging hydrides or cations), triboracyclopropenyl-type structures are rings of three boron atoms where substituents at each boron are also coplanar to the ring. Triboracyclopropenyl-containing compounds are extreme cases of inorganic aromaticity. They are the lightest and smallest cyclic structures known to display the bonding and magnetic properties that originate from fully delocalized electrons in orbitals of σ and π symmetry. Although three-membered rings of boron are frequently so highly strained as to be experimentally inaccessible, academic interest in their distinctive aromaticity and possible role as intermediates of borane pyrolysis motivated extensive computational studies by theoretical chemists. Beginning in the late 1980s with mass spectrometry work by Anderson et al. on all-boron clusters, experimental studies of triboracyclopropenyls were for decades exclusively limited to gas-phase investigations of the simplest rings (ions of B3). However, more recent work has stabilized the triboracyclopropenyl moiety via coordination to donor ligands or transition metals, dramatically expanding the scope of its chemistry.
References
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- ↑ Talebpour A, Bandrauk AD, Yang J, Chin SL (1999). "Multiphoton ionization of inner-valence electrons and fragmentation of ethylene in an intense Ti:sapphire laser pulse". Chemical Physics Letters. 313 (5–6): 789–794. Bibcode:1999CPL...313..789T. doi:10.1016/s0009-2614(99)01075-1.
- ↑ Talebpour A, Bandrauk AD, Vijayalakshmi K, Chin SL (2000). "Dissociative ionization of benzene in intense ultra-fast laser pulses". Journal of Physics B: Atomic, Molecular and Optical Physics. 33 (21): 4615–4626. Bibcode:2000JPhB...33.4615T. doi:10.1088/0953-4075/33/21/307.
- ↑ Laskin J, Futrell JH (2005). "Activation of large ions in FT-ICR mass spectrometry". Mass Spectrometry Reviews. 24 (2): 135–67. Bibcode:2005MSRv...24..135L. doi:10.1002/mas.20012. PMID 15389858.
- ↑ Polfer NC, Oomens J (2007). "Reaction products in mass spectrometry elucidated with infrared spectroscopy". Physical Chemistry Chemical Physics. 9 (29): 3804–17. Bibcode:2007PCCP....9.3804P. doi:10.1039/b702993b. PMID 17637973. S2CID 23485300.
- ↑ Fielicke, André (2023). "Probing the binding and activation of small molecules by gas-phase transition metal clusters via IR spectroscopy". Chemical Society Reviews. 52 (11): 3778–3841. doi: 10.1039/D2CS00104G . ISSN 0306-0012.
- ↑ Gruene P, Rayner DM, Redlich B, van der Meer AF, Lyon JT, Meijer G, Fielicke A (2008). "Structures of Neutral Au7, Au19, and Au20 Clusters in the Gas Phase". Science. 321 (5889): 674–6. Bibcode:2008Sci...321..674G. doi:10.1126/science.1161166. hdl: 11858/00-001M-0000-0010-FC2A-A . PMID 18669858.
- ↑ Martens J, van Outersterp RE, Vreeken RJ, Cuyckens F, Coene KL, Engelke UF, et al. (January 2020). "Infrared ion spectroscopy: New opportunities for small-molecule identification in mass spectrometry - A tutorial perspective". Analytica Chimica Acta. 1093: 1–15. doi:10.1016/j.aca.2019.10.043. hdl: 2066/212342 . PMID 31735202.
- ↑ Martens J, Berden G, van Outersterp RE, Kluijtmans LA, Engelke UF, van Karnebeek CD, et al. (June 2017). "Molecular identification in metabolomics using infrared ion spectroscopy". Scientific Reports. 7 (1): 3363. doi:10.1038/s41598-017-03387-4. PMC 5469762 . PMID 28611404.
- ↑ van Geenen FA, Kranenburg RF, van Asten AC, Martens J, Oomens J, Berden G (February 2021). "Isomer-Specific Two-Color Double-Resonance IR2MS3 Ion Spectroscopy Using a Single Laser: Application in the Identification of Novel Psychoactive Substances". Analytical Chemistry. 93 (4): 2687–2693. doi:10.1021/acs.analchem.0c05042. PMC 7859929 . PMID 33470107.
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