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.
Electrospray ionization (ESI) is a technique used in mass spectrometry to produce ions using an electrospray in which a high voltage is applied to a liquid to create an aerosol. It is especially useful in producing ions from macromolecules because it overcomes the propensity of these molecules to fragment when ionized. ESI is different from other ionization processes since it may produce multiple-charged ions, effectively extending the mass range of the analyser to accommodate the kDa-MDa orders of magnitude observed in proteins and their associated polypeptide fragments.
Koichi Tanaka is a Japanese electrical engineer who shared the Nobel Prize in Chemistry in 2002 for developing a novel method for mass spectrometric analyses of biological macromolecules with John Bennett Fenn and Kurt Wüthrich.
The history of mass spectrometry has its roots in physical and chemical studies regarding the nature of matter. The study of gas discharges in the mid 19th century led to the discovery of anode and cathode rays, which turned out to be positive ions and electrons. Improved capabilities in the separation of these positive ions enabled the discovery of stable isotopes of the elements. The first such discovery was with the element neon, which was shown by mass spectrometry to have at least two stable isotopes: 20Ne and 22Ne. Mass spectrometers were used in the Manhattan Project for the separation of isotopes of uranium necessary to create the atomic bomb.
In mass spectrometry, direct analysis in real time (DART) is an ion source that produces electronically or vibronically excited-state species from gases such as helium, argon, or nitrogen that ionize atmospheric molecules or dopant molecules. The ions generated from atmospheric or dopant molecules undergo ion-molecule reactions with the sample molecules to produce analyte ions. Analytes with low ionization energy may be ionized directly. The DART ionization process can produce positive or negative ions depending on the potential applied to the exit electrode.
Thermospray is a soft ionization source by which a solvent flow of liquid sample passes through a very thin heated column to become a spray of fine liquid droplets. As a form of atmospheric pressure ionization in mass spectrometry these droplets are then ionized via a low-current discharge electrode to create a solvent ion plasma. A repeller then directs these charged particles through the skimmer and acceleration region to introduce the aerosolized sample to a mass spectrometer. It is particularly useful in liquid chromatography-mass spectrometry (LC-MS).
Desorption electrospray ionization (DESI) is an ambient ionization technique that can be coupled to mass spectrometry (MS) for chemical analysis of samples at atmospheric conditions. Coupled ionization sources-MS systems are popular in chemical analysis because the individual capabilities of various sources combined with different MS systems allow for chemical determinations of samples. DESI employs a fast-moving charged solvent stream, at an angle relative to the sample surface, to extract analytes from the surfaces and propel the secondary ions toward the mass analyzer. This tandem technique can be used to analyze forensics analyses, pharmaceuticals, plant tissues, fruits, intact biological tissues, enzyme-substrate complexes, metabolites and polymers. Therefore, DESI-MS may be applied in a wide variety of sectors including food and drug administration, pharmaceuticals, environmental monitoring, and biotechnology.
Robert Graham Cooks is the Henry Bohn Hass Distinguished Professor of Chemistry in the Aston Laboratories for Mass Spectrometry at Purdue University. He is an ISI Highly Cited Chemist, with over 1,000 publications and an H-index of 144.
Desorption atmospheric pressure photoionization (DAPPI) is an ambient ionization technique for mass spectrometry that uses hot solvent vapor for desorption in conjunction with photoionization. Ambient Ionization techniques allow for direct analysis of samples without pretreatment. The direct analysis technique, such as DAPPI, eliminates the extraction steps seen in most nontraditional samples. DAPPI can be used to analyze bulkier samples, such as, tablets, powders, resins, plants, and tissues. The first step of this technique utilizes a jet of hot solvent vapor. The hot jet thermally desorbs the sample from a surface. The vaporized sample is then ionized by the vacuum ultraviolet light and consequently sampled into a mass spectrometer. DAPPI can detect a range of both polar and non-polar compounds, but is most sensitive when analyzing neutral or non-polar compounds. This technique also offers a selective and soft ionization for highly conjugated compounds.
Ambient ionization is a form of ionization in which ions are formed in an ion source outside the mass spectrometer without sample preparation or separation. Ions can be formed by extraction into charged electrospray droplets, thermally desorbed and ionized by chemical ionization, or laser desorbed or ablated and post-ionized before they enter the mass spectrometer.
In mass spectrometry, liquid junction interface is an ion source or set-up that couples peripheric devices, such as capillary electrophoresis, to mass spectrometry.
Renato Zenobi is a Swiss chemist. He is Professor of Chemistry at ETH Zurich. Throughout his career, Zenobi has contributed to the field of analytical chemistry.
Extractive electrospray ionization (EESI) is a spray-type, ambient ionization source in mass spectrometry that uses two colliding aerosols, one of which is generated by electrospray. In standard EESI, syringe pumps provide the liquids for both an electrospray and a sample spray. In neutral desorption EESI (ND-EESI), the liquid for the sample aerosol is provided by a flow of nitrogen.
Paper spray ionization is a technique used in mass spectrometry to produce ions from a sample to be analyzed. It is a variant of electrospray ionization. The sample is applied to a piece of paper and solvent is added. Then a high voltage is applied, which creates the ions to be analyzed with a mass spectrometer. The method, first described in 2010, is relatively easy to use and can detect and measure the presence of various substances in the sample. This technique shows great potential for point-of-care clinical applications, in that important tests may be run and results obtained within a reasonable amount of time in proximity to the patient in a single visit.
Gary Glish is an American analytical chemist at the University of North Carolina at Chapel Hill. He is a leading researcher in the fields of mass spectrometry, ion chemistry, and biomolecule analysis.
The MasSpec Pen, or the precìso MasSpec Pen System, is a mass spectrometry (MS) based cancer detection and diagnosis system that can be used for ex vivo and in vivo tissue sample analysis. The system collects biological molecules from a tissue sample surface via a solid-liquid extraction mechanism and transports the molecules to a mass spectrometer for analysis. The composition of the extracted molecules can then be used to predict if the tissue sample analyzed contains cancerous cells using machine learning algorithms and statistical models. In early-stage clinical research, the MasSpec Pen system was able to distinguish various cancer tissues, including thyroid, breast, lung, and ovarian tumor tissues, from their normal counterparts with an overall accuracy of 96.3%. A follow-up study in illustrating the use of the device for detection of serous ovarian carcinoma in ex vivo tissue biopsies allowed for the discrimination of normal and cancerous ovarian samples with a clinical sensitivity and specificity of 94.0% and 94.4%, respectively.
Livia Schiavinato Eberlin is a Brazilian analytical chemist who won a MacArthur "Genius" Fellowship for her research on the use of mass spectrometry to detect cancerous tissue.
Peter Nemes is a Hungarian-American chemist, who is active in the fields of bioanalytical chemistry, mass spectrometry, cell/developmental biology, neuroscience, and biochemistry.
Abraham Badu-Tawiah is a Ghanaian scientist who is an Associate Professor of Chemistry at the Ohio State University. His research considers the development of mass spectrometry for the detection of disease. In 2017 he was awarded the American Chemical Society Arthur F. Findeis prize and in 2020 a Sloan Research Fellowship.
Julia Laskin is the William F. and Patty J. Miller Professor of Analytical Chemistry at Purdue University. Her research is focused on the fundamental understanding of ion-surface collisions, understanding of phenomena underlying chemical analysis of large molecules in complex heterogeneous environments, and the development of new instrumentation and methods in preparative and imaging mass spectrometry.
