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Mass Spectrometric Analysis
Published in Adorjan Aszalos, Modern Analysis of Antibiotics, 2020
Chemical ionization has been used frequently because it is available in most laboratories and generally give intense protonated molecular ions of basic macrolides. Isobutane and ammonia CI were used to confirm the structures of two antibiotics, M-4365A2 and M-4365G2 [169]. The isobutane and ammonia mass spectra were very similar; in addition to protonated molecular ions, decomposition ions corresponding to aglycones, protonated desosamine, and loss of water were observed. Exchangeable protons were determined from the mass shifts using deuterated ammonia. Deuterated methane and iso-butane gave (M + D)+ ions but did not exchange deuterium with other protons. To help elucidate the spectra of M-4365A2 and M-4365G2, five other 16-membered basic macrolides were examined.
Basics Of Gas Chromatography Mass Spectrometry System
Published in Raquel Cumeras, Xavier Correig, Volatile organic compound analysis in biomedical diagnosis applications, 2018
William Hon Kit Cheung, Raquel Cumeras
However, in some instances electron impact ionization may be too excessive and cause the molecular ion to be present in low abundance or even absent, resulting in inaccurate chemical matching and chemical formula generation. Chemical ionization is a softer form of ionization (x < 10 eV), which uses reagent gas such as isobutene, ammonia, methane or carbon dioxide to create a cloud of charge ion to transfer the charge to the analyte (charge transfer reaction). CI does not induce excesses fragmentation due to the low collisional energy used and can be used determine the molecular weight of the parent compound for structure elucidation. CI can be applied in either positive or negative mode polarity; most small scale molecules are able to form positive ions, however, in order to generate a negative ion, the molecule must be able to generate a stable negative charge such as those containing acidic functional groups or halogenated compounds.
Gas Chromatography
Published in Joseph Chamberlain, The Analysis of Drugs in Biological Fluids, 2018
For the operation of the mass spectrometer, the sample needs to be at low pressure in the source. Consequently, using conventional packed columns the carrier gas has to be separated from the analyte. Several ingenious separators have been designed to enable the separation to be as efficient as possible to ensure that most of the sample reaches the detector to maintain sensitivity. To obtain the best sensitivity, the use of chemical ionization has become widespread (Table 6.9)
Mass spectrometry based metabolomics for small molecule metabolites mining and confirmation as potential biomarkers for schistosomiasis – case of the Okavango Delta communities in Botswana
Published in Expert Review of Proteomics, 2022
Sedireng M. Ndolo, Matshediso Zachariah, Lebotse Molefi, Nthabiseng Phaladze, Kwenga F. Sichilongo
Table 1 summarizes the instrumentation, methods, ionization modes, columns, data filtration, and statistical evaluation techniques that have been employed in schistosomiasis metabolomics involving separation science and mass spectrometry for small molecules. Table 1 also emphasizes that there is very little literature on the metabolomics of schistosomiasis using either LC-MS or GC-MS. This underscores the tag attached to this disease, i.e. ‘a neglected tropical disease,’ which is the case despite affecting over a quarter of a billion people globally. The most commonly used ionization mode is electrospray ionization (ESI) for LC-MS and electron ionization (EI) for GC-MS. Future studies could focus on interrogating other ionization techniques, such as atmospheric pressure chemical ionization (APCI). This is well suited for small-molecule ionization using LC-MS and soft ionization, such as field desorption, in addition to chemical ionization for GC-MS. These techniques need to be probed for the analysis of abundant metabolites during ionization. There is a need to explore other data filtration software packages, in addition to XCMS, in order to increase the chances of biomarker discovery. This applies to multivariate statistical tools that revolve around PCA and PLS-DA.
Metabolism of cyclic phenones in rainbow trout in vitro assays
Published in Xenobiotica, 2020
Jose Serrano, Mark A. Tapper, Richard C. Kolanczyk, Barbara R. Sheedy, Tylor Lahren, Dean E. Hammermeister, Jeffrey S. Denny, Michael W. Hornung, Alena Kubátová, Patricia A. Kosian, Jessica Voelker, Patricia K. Schmieder
Hexane extracts of TEDG buffer, binding cytosols, and slice exposure media were analyzed by GC-MS for parent chemicals and metabolites with adequate volatility, sensitivity and thermal stability. Extracts were analyzed on an Agilent 6890 N gas chromatograph connected to either an Agilent 5975 Inert XL or Agilent 5973 mass selective detector (Agilent Technologies, Santa Clara, CA, USA) using the conditions reported by Tapper et al. (2018b) and reproduced in Supplemental Table 1. Electron and chemical ionization approaches were used for qualitative analyses. Selected- or total-ion methods were used for quantitative studies (see Data analysis section). Due to the limited quantity of metabolites formed, chemical derivatization with BSTFA or MSTFA was performed in some 24 h slice-incubated CPK samples prior to GC-MS as described by Segura et al. (1998) to confirm the presence, relative yield and thermal stability of hydroxylated CPK metabolites in reaction mixtures (Serrano et al., 2019).
Recent advances in the metabolomic study of bladder cancer
Published in Expert Review of Proteomics, 2019
Chandra Sekhar Amara, Venkatrao Vantaku, Yair Lotan, Nagireddy Putluri
Detection and quantitation of the analytes using MS are dependent on the separation of analytes prior to mass analysis [45–47]. To isolate proteins from biological specimens or to separate small molecules or chemically diverse metabolites that are bound to the protein matrix, methanol is used prior to metabolomic analysis. Determination of different classes of metabolites requires the application of different solvents for extraction. Hence, aliquoted samples are prepared from the same biological specimen (for example plasma or urine samples from a cancer patient) and subjected to different extraction protocols to be analyzed under various chromatographic separations. Next, the analytes will be ionized for detection with the MS platform. Several ionization techniques have been described previously based on the chromatographic methodology (e.g., electron, cold or chemical ionization used in gas chromatography; electrospray ionization (ESI), atmospheric pressure chemical ionization used in liquid chromatography). Among these ionization techniques, ESI is the most widely used method.