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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.
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. 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.
Gas chromatography–mass spectrometry (GC–MS) is an analytical method that combines the features of gas-chromatography and mass spectrometry to identify different substances within a test sample. Applications of GC–MS include drug detection, fire investigation, environmental analysis, explosives investigation, food and flavor analysis, and identification of unknown samples, including that of material samples obtained from planet Mars during probe missions as early as the 1970s. GC–MS can also be used in airport security to detect substances in luggage or on human beings. Additionally, it can identify trace elements in materials that were previously thought to have disintegrated beyond identification. Like liquid chromatography–mass spectrometry, it allows analysis and detection even of tiny amounts of a substance.
In mass spectrometry, the quadrupole mass analyzer is a type of mass analyzer originally conceived by Nobel laureate Wolfgang Paul and his student Helmut Steinwedel. As the name implies, it consists of four cylindrical rods, set parallel to each other. In a quadrupole mass spectrometer (QMS) the quadrupole is the mass analyzer – the component of the instrument responsible for selecting sample ions based on their mass-to-charge ratio (m/z). Ions are separated in a quadrupole based on the stability of their trajectories in the oscillating electric fields that are applied to the rods.
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.
Liquid chromatography–mass spectrometry (LC–MS) is an analytical chemistry technique that combines the physical separation capabilities of liquid chromatography with the mass analysis capabilities of mass spectrometry (MS). Coupled chromatography – MS systems are popular in chemical analysis because the individual capabilities of each technique are enhanced synergistically. While liquid chromatography separates mixtures with multiple components, mass spectrometry provides spectral information that may help to identify each separated component. MS is not only sensitive, but provides selective detection, relieving the need for complete chromatographic separation. LC–MS is also appropriate for metabolomics because of its good coverage of a wide range of chemicals. This tandem technique can be used to analyze biochemical, organic, and inorganic compounds commonly found in complex samples of environmental and biological origin. Therefore, LC–MS may be applied in a wide range of sectors including biotechnology, environment monitoring, food processing, and pharmaceutical, agrochemical, and cosmetic industries. Since the early 2000s, LC–MS has also begun to be used in clinical applications.
Ion mobility spectrometry (IMS) It is a method of conducting analytical research that separates and identifies ionized molecules present in the gas phase based on the mobility of the molecules in a carrier buffer gas. Even though it is used extensively for military or security objectives, such as detecting drugs and explosives, the technology also has many applications in laboratory analysis, including studying small and big biomolecules. IMS instruments are extremely sensitive stand-alone devices, but are often coupled with mass spectrometry, gas chromatography or high-performance liquid chromatography in order to achieve a multi-dimensional separation. They come in various sizes, ranging from a few millimeters to several meters depending on the specific application, and are capable of operating under a broad range of conditions. IMS instruments such as microscale high-field asymmetric-waveform ion mobility spectrometry can be palm-portable for use in a range of applications including volatile organic compound (VOC) monitoring, biological sample analysis, medical diagnosis and food quality monitoring. Systems operated at higher pressure are often accompanied by elevated temperature, while lower pressure systems (1–20 hPa) do not require heating.
Atmospheric pressure chemical ionization (APCI) is an ionization method used in mass spectrometry which utilizes gas-phase ion-molecule reactions at atmospheric pressure (105 Pa), commonly coupled with high-performance liquid chromatography (HPLC). APCI is a soft ionization method similar to chemical ionization where primary ions are produced on a solvent spray. The main usage of APCI is for polar and relatively less polar thermally stable compounds with molecular weight less than 1500 Da. The application of APCI with HPLC has gained a large popularity in trace analysis detection such as steroids, pesticides and also in pharmacology for drug metabolites.
In mass spectrometry, Orbitrap is an ion trap mass analyzer consisting of an outer barrel-like electrode and a coaxial inner spindle-like electrode that traps ions in an orbital motion around the spindle. The image current from the trapped ions is detected and converted to a mass spectrum using the Fourier transform of the frequency signal.
Surface-enhanced laser desorption/ionization (SELDI) is a soft ionization method in mass spectrometry (MS) used for the analysis of protein mixtures. It is a variation of matrix-assisted laser desorption/ionization (MALDI). In MALDI, the sample is mixed with a matrix material and applied to a metal plate before irradiation by a laser, whereas in SELDI, proteins of interest in a sample become bound to a surface before MS analysis. The sample surface is a key component in the purification, desorption, and ionization of the sample. SELDI is typically used with time-of-flight (TOF) mass spectrometers and is used to detect proteins in tissue samples, blood, urine, or other clinical samples, however, SELDI technology can potentially be used in any application by simply modifying the sample surface.
Protein mass spectrometry refers to the application of mass spectrometry to the study of proteins. Mass spectrometry is an important method for the accurate mass determination and characterization of proteins, and a variety of methods and instrumentations have been developed for its many uses. Its applications include the identification of proteins and their post-translational modifications, the elucidation of protein complexes, their subunits and functional interactions, as well as the global measurement of proteins in proteomics. It can also be used to localize proteins to the various organelles, and determine the interactions between different proteins as well as with membrane lipids.
Quantitative proteomics is an analytical chemistry technique for determining the amount of proteins in a sample. The methods for protein identification are identical to those used in general proteomics, but include quantification as an additional dimension. Rather than just providing lists of proteins identified in a certain sample, quantitative proteomics yields information about the physiological differences between two biological samples. For example, this approach can be used to compare samples from healthy and diseased patients. Quantitative proteomics is mainly performed by two-dimensional gel electrophoresis (2-DE), preparative native PAGE, or mass spectrometry (MS). However, a recent developed method of quantitative dot blot (QDB) analysis is able to measure both the absolute and relative quantity of an individual proteins in the sample in high throughput format, thus open a new direction for proteomic research. In contrast to 2-DE, which requires MS for the downstream protein identification, MS technology can identify and quantify the changes.
Sample preparation for mass spectrometry is used for the optimization of a sample for analysis in a mass spectrometer (MS). Each ionization method has certain factors that must be considered for that method to be successful, such as volume, concentration, sample phase, and composition of the analyte solution. Quite possibly the most important consideration in sample preparation is knowing what phase the sample must be in for analysis to be successful. In some cases the analyte itself must be purified before entering the ion source. In other situations, the matrix, or everything in the solution surrounding the analyte, is the most important factor to consider and adjust. Often, sample preparation itself for mass spectrometry can be avoided by coupling mass spectrometry to a chromatography method, or some other form of separation before entering the mass spectrometer. In some cases, the analyte itself must be adjusted so that analysis is possible, such as in protein mass spectrometry, where usually the protein of interest is cleaved into peptides before analysis, either by in-gel digestion or by proteolysis in solution.
Two-dimensional chromatography is a type of chromatographic technique in which the injected sample is separated by passing through two different separation stages. Two different chromatographic columns are connected in sequence, and the effluent from the first system is transferred onto the second column. Typically the second column has a different separation mechanism, so that bands that are poorly resolved from the first column may be completely separated in the second column. Alternately, the two columns might run at different temperatures. During the second stage of separation the rate at which the separation occurs must be faster than the first stage, since there is still only a single detector. The plane surface is amenable to sequential development in two directions using two different solvents.
Ion mobility spectrometry–mass spectrometry (IMS-MS) is an analytical chemistry method that separates gas phase ions based on their interaction with a collision gas and their masses. In the first step, the ions are separated according to their mobility through a buffer gas on a millisecond timescale using an ion mobility spectrometer. The separated ions are then introduced into a mass analyzer in a second step where their mass-to-charge ratios can be determined on a microsecond timescale. The effective separation of analytes achieved with this method makes it widely applicable in the analysis of complex samples such as in proteomics and metabolomics.
Label-free quantification is a method in mass spectrometry that aims to determine the relative amount of proteins in two or more biological samples. Unlike other methods for protein quantification, label-free quantification does not use a stable isotope containing compound to chemically bind to and thus label the protein.
Capillary electrophoresis–mass spectrometry (CE–MS) is an analytical chemistry technique formed by the combination of the liquid separation process of capillary electrophoresis with mass spectrometry. CE–MS combines advantages of both CE and MS to provide high separation efficiency and molecular mass information in a single analysis. It has high resolving power and sensitivity, requires minimal volume and can analyze at high speed. Ions are typically formed by electrospray ionization, but they can also be formed by matrix-assisted laser desorption/ionization or other ionization techniques. It has applications in basic research in proteomics and quantitative analysis of biomolecules as well as in clinical medicine. Since its introduction in 1987, new developments and applications have made CE-MS a powerful separation and identification technique. Use of CE–MS has increased for protein and peptides analysis and other biomolecules. However, the development of online CE–MS is not without challenges. Understanding of CE, the interface setup, ionization technique and mass detection system is important to tackle problems while coupling capillary electrophoresis to mass spectrometry.
A direct electron ionization liquid chromatography–mass spectrometry interface is a technique for coupling liquid chromatography and mass spectrometry (LC-MS) based on the direct introduction of the liquid effluent into an electron ionization (EI) source. Library searchable mass spectra are generated. Gas-phase EI has many applications for the detection of HPLC amenable compounds showing minimal adverse matrix effects. The direct-EI LC-MS interface provides access to well-characterized electron ionization data for a variety of LC applications and readily interpretable spectra from electronic libraries for environmental, food safety, pharmaceutical, biomedical, and other applications.
Isobaric labeling is a mass spectrometry strategy used in quantitative proteomics. Peptides or proteins are labeled with chemical groups that have identical mass (isobaric), but vary in terms of distribution of heavy isotopes in their structure. These tags, commonly referred to as tandem mass tags, are designed so that the mass tag is cleaved at a specific linker region upon high-energy CID (HCD) during tandem mass spectrometry yielding reporter ions of different masses. The most common isobaric tags are amine-reactive tags. However, tags that react with cysteine residues and carbonyl groups have also been described. These amine-reactive groups go through N-hydroxysuccinimide (NHS) reactions, which are based around three types of functional groups. Isobaric labeling methods include tandem mass tags (TMT), isobaric tags for relative and absolute quantification (iTRAQ), mass differential tags for absolute and relative quantification, and dimethyl labeling. TMTs and iTRAQ methods are most common and developed of these methods. Tandem mass tags have a mass reporter region, a cleavable linker region, a mass normalization region, and a protein reactive group and have the same total mass.
References
- ↑ Guevremont R (November 2004). "High-field asymmetric waveform ion mobility spectrometry: a new tool for mass spectrometry". J Chromatogr A. 1058 (1–2): 3–19. doi:10.1016/S0021-9673(04)01478-5. PMID 15595648.
- ↑ Kolakowski BM, Mester Z (September 2007). "Review of applications of high-field asymmetric waveform ion mobility spectrometry (FAIMS) and differential mobility spectrometry (DMS)". Analyst. 132 (9): 842–64. Bibcode:2007Ana...132..842K. doi:10.1039/b706039d. PMID 17710259.
- ↑ Лосев, В.В.; Кумпаненко, И.В.; Рощин, А.В. (2007). "Спектроскопия подвижности ионов — перспективный метод обнаружения химически опасных веществ в многокомпонентных воздушных средах" [Ion mobility spectroscopy is a promising method for the detection of chemically hazardous substances in multicomponent air environments]. Химическая физика (in Russian). 26 (10): 33–42.
- 1 2 Swearingen, Kristian E; Moritz, Robert L (2012). "High-field asymmetric waveform ion mobility spectrometry for mass spectrometry-based proteomics". Expert Review of Proteomics. Informa UK Limited. 9 (5): 505–517. doi:10.1586/epr.12.50. ISSN 1478-9450. PMC 4777519 . PMID 23194268.
- ↑ "Детектор паров взрывчатых веществ МО-2М". ООО "Сибел" (in Russian).
- ↑ Капустин, В.И.; Коржавый, А.П. (2016). "Дрейф-спектрометрия: традиционные методы и перспективы развития" [Drift spectrometry: traditional methods and development prospects]. Российский технологический журнал [Russian Technological Journal] (in Russian). 4 (2): 3–24. doi: 10.32362/2500-316X-2016-4-2-3-24 .