Ion in mass spectrometry

The stability of isothiazole derives from the fact that it has an aromatic delocalized ir-electron system. The NMR chemical shifts, which depend, inter alia, on ring currents, and the high stability of the molecular ions in mass spectrometry, are typical of aromatic compounds, and X-ray measurements confirm the partial double bond character of all the bonds of the ring. 

Electron impact (Section 13.22) Method for producing positive ions in mass spectrometry whereby a molecule is bombarded by high-energy electrons. 

Varied Methane Cations. The methane molecular ion (methane radical cation, CH4+ ), the parent ion in mass spectrometry, and the methane dication (CH42+) are of great significance and have been studied both experimentally and theoretically.800 802 Recent advanced studies have shown that the methane radical cation, CH4+ has a fivecoordinate planar structure as suggested in early calculations by Olah and Klopman.800... 

The mass determination of ionic species (atomic or polyatomic ions) in mass spectrometry is always a comparative measurement, which means the mass of an ionic species is determined with respect to reference masses of elements (or substances) used for mass calibration. The reference mass is thus acquired from the mass unit (m = In = 1/12) of the mass of the neutral carbon isotope (m = 1.66 X 10 kg). A mass calibration is easy to perform in solid-state mass spectrometry if the sample contains carbon (using carbon cluster ions with whole masses, as discussed above). The so-called doublet method was apphed formerly, e.g., ions and doubly charged Mg + forming a doublet at the same nominal mass number 12 were considered, where they are slightly displaced with respect to one another. The doublet method is no longer of relevance in modern inorganic mass spectrometry. Orientation in the mass spectra can be carried out via the matrix, minor and trace elements after mass calibration and by comparing the measured isotopic pattern of elements with theoretical values. 

In many cases the mere observation of a parent negative ion in mass spectrometry or ion mobility spectrometry is evidence of the positive electron affinity of a molecule. The ECD kinetic model is applicable to the ions observed in NICI experiments so the same quantities measured in the ECD can also be measured with this technique. There is a large body of NIMS data taken at two temperatures for compounds significant to those used in environmental chemistry that can be analyzed to obtain approximate electron affinities and activation energies [10]. 

Methods for producing ions in mass spectrometry with a chromatographic sample inlet MM = molecular mass... 

Developments in two general areas have spurred this progress. Sector and quadrupole mass analyzers, the traditional methods of separation of ions in mass spectrometry, have recently been complemented by the development of powerful Foiuier transform (FT-MS) and time-of-flight (TOF-MS) instruments. The TOF analyzers are particularly well-suited for detecting higher molar-mass species present in polymers. 

Molecular ion In mass spectrometry, the species formed by loss of an electron from a molecule. 

The ions in mass spectrometry may be formed in a variety of ways. One method for converting molecules to ions (ionization) in a mass spectrometer is to place a sample under high vacuum and bombard it with a beam of high-energy electrons ( 70 eV, or 6.7 X 10 kj mop ). This method is called electron impact (El) ionization mass spectrometry. The impact of the electron beam dislodges a valence electron from the gas-phase molecules, leaving them with a -El charge and an unshared electron. This species is called the molecular ion (M ). We can represent this process as follows ... 

Holmes, J.L. Aubry, C. Meyer, RM. Assigning Structures to Ions in Mass Spectrometry. Taylor Francis Boca Raton, FL, 2006. 

Shimizu, T, Watanabe-Ezoe, Y., Yamaguchi, S., Tsukatani, H., Imasaka,T, Zaitsu, S., Uchimura,T, Imasaka,T. (2010) Enhancement of molecular ions in mass spectrometry using an ultrashort optical pulse in multiphoton ionization. Anal. Chem.,82,3441-3444. 

Mayer PM, Poon C (2009) The mechanisms of collisional activation of ions in mass spectrometry. Mass Spectrom Rev 28 608-639... 

The ions in mass spectrometry may be formed in a variety of ways. One method for converting molecules to ions (ionization) in a mass spectrometer is to place a sample under high vacuum and bombard it with a beam of high-energy electrons (—70 eV, or —6.7 X 10 kJ mol ). 

Minimum energy that must be imparted to an atom or molecule to produce a detectable amount of a specified ion. In mass spectrometry it is the voltage, which corresponds to the minimum electron energy necessary for the production of a given fragment ion. The term appearance potential (AP) is deprecated. 

Holmes JL and Benoit FM (1972) Metastable ions in mass spectrometry. In Maccoll A (ed) MTP International Review of Science, Physical Chemistry, Series One, Vol 5, pp 259-300. London Butterworth. 

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