CHEMICAL IONISATION MASS SPECTROSCOPY

Mottram, H.R., Evershed, R.P. 2001. Elucidation of the composition of bovine milk fat triacylglycerols using high-performance liquid chromatography-atmospheric pressure chemical ionisation mass spectroscopy. J. Chromatogr. A., 926, 239-253. 

Most of the compounds identified gave observable molecular ions in electron impact mass spectrometry. Chemical ionisation mass spectroscopy with isobutane was carried out to determine the relative molecular masses. In all instances, the quasi-molecular ion was M + 1 with a relative abundance of 10% no M + 57 was observed. Some compounds were identified on the basis of their mass spectra only because no reference compounds were obtainable. 

High-resolution mass spectra were obtained for unidentified compounds a, b, c, d, and f. The molecular formula of compounds a, b, c, and d is C12H22O. Proposed structures are isomers of ketones, e.g., a and b might be 2- or 4-isomers of ethylisopropyl cyclohexyl ketone and c and d might be cyclohex-4-ylhexan-2-one or cyclohex-4-yl-4-methylpentan-2-one, respectively. An unidentified compound (e) was found also for the quasi-molecular ion M + 1105. The only fragment was M - 18 in chemical ionisation mass spectroscopy. The molecular formula of unidentified compound f is C15H14O. The proposed structure is... 

Determined by chemical ionisation mass spectroscopy The relative intensities of major peaks in the mass spectra are given in parentheses ... 

Resonance (NMR) spectroscopy, InfraRed (IR) absorption, Gas Chromatography / Electron Ionisation - Mass Spectometry (GC/EI-MS) and by Gas Chromatography / Chemical Ionisation - Mass Spectrometry (GC/CI-MS)(see below for fiirther details of the analyses). 

NMR) [24], and Fourier transform-infrared (FT-IR) spectroscopy [25] are commonly applied methods. Analysis using mass spectrometric (MS) techniques has been achieved with gas chromatography-mass spectrometry (GC-MS), with chemical ionisation (Cl) often more informative than conventional electron impact (El) ionisation [26]. For the qualitative and quantitative characterisation of silicone polyether copolymers in particular, SEC, NMR, and FT-IR have also been demonstrated as useful and informative methods [22] and the application of high-temperature GC and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) is also described [5]. 

Mass spectroscopy [electron ionisation (El), chemical ionisation (Cl), electrospray ionisation (ESI), fast atom bombardment (FAB), matrix-associated laser desorption ionisation (MALDI), inductively coupled plasma-mass spectrmetry (ICP-MS, cf and ), etc]... 

Udseth and Friedman [18] carried out a mass spectroscopy (MS) study of PS with a molecular weight of 21,000. The PS was evaporated from a probe filament heated at 1000 °C/s under both electron ionisation (El) and methane and argon chemical... 

Ballistreri and co-workers [59] examined the primary thermal decomposition mechanism of this polymer by Py-MS. Several MS techniques were used to identify compounds present in the pyrolysis mixture comparison of electron impact and chemical ionisation spectra, high resolution accurate mass measurements and tandem mass spectroscopy (daughter and parent ion spectra). The results obtained indicate that intramolecular exchange reactions predominate in the primary thermal fragmentation processes yielding cyclic oligomers up to tetramer. No other pyrolysis products were detectable. 

The structures of three bacillomycins D, F and L have been completely established as (59), (58) and (60) respectively. All of them contained the characteristic iturinic acids and seven a-amino acids. The sequence of amino acids was studied using chemical methods, in particular Edman degradation of the product obtained by specific cleavage of the peptide moiety with N-bromosuccinimide. Confirmatory results were obtained by chemical ionisation (isobutane) mass spectrometry and various techniques of NMR spectroscopy. The exact molecular weights of the various species were obtained by FAB mass spectrometry 146, 147) (see Table 7). 

In recent years higher field H-n.m.r. spectroscopy and new mass spectroscopic methods (chemical ionisation, field desorption, FAB and Mikes technique) became available. Recently Baldwin etal. (2) applied some of these new mass spectroscopic techniques to the structure determination of some bruceolides. A detailed C-n.m.r. study of a number of quassinoids has been published (Si) and C-n.n.r. data have since then been recorded in most of the papers dealing with constituents of Simaroubaceae. X-Ray analysis has also become more accessible and structures of many quassinoids are now being established by this method. 

Kassalainen and Williams [135] coupled thermal field flow fractionation (ThFFF) and matrix-assisted laser desorption/ionisation time-of-flight mass spectroscopy (MALDI-ToF-MS) to yield a powerful combination of techniques for the analysis of polydisperse PS. ThFFF high selectivity and sensitivity to chemical composition were used to separate polydisperse polymers and polymer mixtures into the narrow polydispersity and homogeneous chemical composition fractions essential for MAT.DT-ToF-MS analyses. On the other hand, because it is possible to measure directly using MALDI-ToF-MS, it alleviates the need for polymer standards for ThFFF. Kassalainen and Williams [135] address the coupling of ThFFF and MALDI-ToF-MS and identify compatibility issues. Optimum conditions were determined and developed to maximise the capabilities of the combined technique. Depending on the polymer and the method of matrix-assisted laser desorption/ionisation (MALDI) sample deposition, fractions from 1-10 ThFFF runs were combined for MALDI-ToF-MS analysis. Binary solvents are used to enhance ThFFF retention and resolution of low (<15 kDa) polymers, and methods developed to allow routine MALDI-ToF-MS analyses of PS polymers up to 575 kDa. Overall, the compatibility of the two techniques was extended from several kilodaltons to several hundred kDa. Polymer... 

Spectroscopy Chemical Ionisation in Mass Spectrometry Chromatography-MS, Methods Hyphenated Techniques, Applications of in Mass Spectrometry Inductively Coupled Plasma Mass Spectrometry, Methods Mass Spectrometry, Historical Perspective MS-MS and MS" Photoacoustic Spectroscopy, Applications. 

Today, atomic emission spectroscopy always makes use of relative quantitation, i. e. unknown samples are quantitatively analysed after calibration with samples of known composition. The most common approach to calibration is internal standardisation. The underlying assumption, introduced by Gerlach in 1925, is that the ratio of the analyte mass to the mass of the internal standard, matching the analyte in its chemical properties, emission wavelength, energy of the line, and ionisation... 

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