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Desorption Atmospheric Pressure Photoionization
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. History The history o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
DAPPI
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. History The history of d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solvent
A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for polar molecules and the most common solvent used by living things; all the ions and proteins in a cell are dissolved in water within the cell. The quantity of solute that can dissolve in a specific volume of solvent varies with temperature. Major uses of solvents are in paints, paint removers, inks, and dry cleaning. Specific uses for organic solvents are in dry cleaning (e.g. tetrachloroethylene); as paint thinners (toluene, turpentine); as nail polish removers and solvents of glue (acetone, methyl acetate, ethyl acetate); in spot removers (hexane, petrol ether); in detergents ( citrus terpenes); and in perfumes (ethanol). Solvents find various applications in chemical, pharmaceutical, oil, and gas industries, including in chemical syn ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemical Polarity
In chemistry, polarity is a separation of electric charge leading to a molecule or its chemical groups having an electric dipole moment, with a negatively charged end and a positively charged end. Polar molecules must contain one or more polar bonds due to a difference in electronegativity between the bonded atoms. Molecules containing polar bonds have no molecular polarity if the bond dipoles cancel each other out by symmetry. Polar molecules interact through dipole–dipole intermolecular forces and hydrogen bonds. Polarity underlies a number of physical properties including surface tension, solubility, and melting and boiling points. Polarity of bonds Not all atoms attract electrons with the same force. The amount of "pull" an atom exerts on its electrons is called its electronegativity. Atoms with high electronegativitiessuch as fluorine, oxygen, and nitrogenexert a greater pull on electrons than atoms with lower electronegativities such as alkali metals and alkaline ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrospray Ionization
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 (e.g. matrix-assisted laser desorption/ionization (MALDI)) 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. Mass spectrometry using ESI is called electrospray ionization mass spectrometry (ESI-MS) or, less commonly, electrospray mass spectrometry (ES-MS). ESI is a so-called 'soft ionization' technique, since there is very little fragmentation. This can be advantageous in the sense that the molecular ion (or more accurately a pseudo molecular ion) is almost alw ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fourier Transform Ion Cyclotron Resonance
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. History FT- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbazole
Carbazole is an aromatic heterocyclic organic compound. It has a tricyclic structure, consisting of two six-membered benzene rings fused on either side of a five-membered nitrogen-containing ring. The compound's structure is based on the indole structure, but in which a second benzene ring is fused onto the five-membered ring at the 2–3 position of indole (equivalent to the 9a–4a double bond in carbazole, respectively). Carbazole is a constituent of tobacco smoke. Synthesis A classic laboratory organic synthesis for carbazole is the Borsche–Drechsel cyclization. In the first step, phenylhydrazine is condensed with cyclohexanone to the corresponding imine. The second step is a hydrochloric acid-catalyzed rearrangement reaction and ring-closing reaction to tetrahydrocarbazole. In one modification, both steps are rolled into one by carrying out the reaction in acetic acid. In the third step, this compound is oxidized by red lead to carbazole itself. Another classic is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coronene
Coronene (also known as superbenzene and cyclobenzene) is a polycyclic aromatic hydrocarbon (PAH) comprising seven peri-fused benzene rings. Its chemical formula is . It is a yellow material that dissolves in common solvents including benzene, toluene, and dichloromethane. Its solutions emit blue light fluorescence under UV light. It has been used as a solvent probe, similar to pyrene. The compound is of theoretical interest to organic chemists because of its aromaticity. It can be described by 20 resonance structures or by a set of three mobile Clar sextets. In the Clar sextet case, the most stable structure for coronene has only the three isolated outer sextets as fully aromatic although superaromaticity would still be possible when these sextets are able to migrate into the next ring. Occurrence and synthesis Coronene occurs naturally as the very rare mineral carpathite, which is characterized by flakes of pure coronene embedded in sedimentary rock. This mineral may be create ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Benzoperylene
Benzo 'ghi''erylene is a polycyclic aromatic hydrocarbon with the chemical formula C22H12. Occurrence and safety Benzo 'ghi''erylene occurs naturally in crude oil and coal tar. It is a product of incomplete combustion and is found in tobacco smoke, automobile exhausts, industrial emissions, grilled meat products and edible oils. In the atmosphere, it is adsorbed to particles and is deposited into the soil and water. The compound accumulates strongly in organisms and the environment, and is suspected to be mutagenic and carcinogenic. It is one of 16 PAHs A polycyclic aromatic hydrocarbon (PAH) is a class of organic compounds that is composed of multiple aromatic rings. The simplest representative is naphthalene, having two aromatic rings and the three-ring compounds anthracene and phenanthrene. ... included in the EPA list of priority pollutants. References Polycyclic aromatic hydrocarbons PBT substances {{hydrocarbon-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Perylene
Perylene or perilene is a polycyclic aromatic hydrocarbon with the chemical formula C20H12, occurring as a brown solid. It or its derivatives may be carcinogenic, and it is considered to be a hazardous pollutant. In cell membrane cytochemistry, perylene is used as a fluorescent lipid probe. It is the parent compound of a class of rylene dyes. Reactions Like other polycyclic aromatic compounds, perylene is reduced by alkali metals to give a deeply colored radical anion and a dianion. The diglyme solvates of these salts have been characterized by X-ray crystallography. Emission Perylene displays blue fluorescence. It is used as a blue-emitting dopant material in OLEDs, either pure or substituted. Perylene can be also used as an organic photoconductor. It has an absorption maximum at 434 nm, and as with all polycyclic aromatic compounds, low water solubility (1.2 x 10−5 mmol/L). Perylene has a molar absorptivity of 38,500 M−1cm−1 at 435.7 nm. Image:Perylene ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Squalene
Squalene is an organic compound. It is a triterpenoid with the formula C30H50. It is a colourless oil, although impure samples appear yellow. It was originally obtained from shark liver oil (hence its name, as ''Squalus'' is a genus of sharks). All plants and animals produce squalene as a biochemical intermediate to sterol biosynthesis. An estimated 12% of bodily squalene in humans is found in Sebaceous gland, sebum. Squalene has a role in topical skin lubrication and protection. Squalene is a precursor (chemistry), precursor for synthesis of all plant and animal sterols, including cholesterol and steroid hormones in the human body. Squalene is an important ingredient in some vaccine adjuvants: The Novartis and GlaxoSmithKline adjuvants are called MF59 and AS03, respectively. Role in steroid synthesis Squalene is the biochemical precursor to steroids. The squalene conversion begins with oxidation (via squalene monooxygenase) of one of its terminal double bonds, resulting in 2,3- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Farnesene
The term farnesene refers to a set of six closely related chemical compounds which all are sesquiterpenes. α-Farnesene and β-farnesene are isomers, differing by the location of one double bond. α-Farnesene is 3,7,11-trimethyl-1,3,6,10-dodecatetraene and β-farnesene is 7,11-dimethyl-3-methylene-1,6,10-dodecatriene. The alpha form can exist as four stereoisomers that differ about the geometry of two of its three internal double bonds (the stereoisomers of the third internal double bond are identical). The beta isomer exists as two stereoisomers about the geometry of its central double bond. Two of the α-farnesene stereoisomers are reported to occur in nature. (''E'',''E'')-α-Farnesene is the most common isomer. It is found in the coating of apples, and other fruits, and it is responsible for the characteristic green apple odour. Its oxidation by air forms compounds that are damaging to the fruit. The oxidation products injure cell membranes which eventually causes cell dea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Matrix-assisted Laser Desorption/ionization
In mass spectrometry, matrix-assisted laser desorption/ionization (MALDI) is an ionization technique that uses a laser energy absorbing matrix to create ions from large molecules with minimal fragmentation. It has been applied to the analysis of biomolecules ( biopolymers such as DNA, proteins, peptides and carbohydrates) and various organic molecules (such as polymers, dendrimers and other macromolecules), which tend to be fragile and fragment when ionized by more conventional ionization methods. It is similar in character to electrospray ionization (ESI) in that both techniques are relatively soft (low fragmentation) ways of obtaining ions of large molecules in the gas phase, though MALDI typically produces far fewer multi-charged ions. MALDI methodology is a three-step process. First, the sample is mixed with a suitable matrix material and applied to a metal plate. Second, a pulsed laser irradiates the sample, triggering ablation and desorption of the sample and matrix materi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
