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Determinative Techniques to Measure Organics and Inorganics
Published in Paul R. Loconto, Trace Environmental Quantitative Analysis, 2020
In the words of Watson (p. 2)73: The most common ionization process, electron-impact (EI), is achieved by bombardment with electrons at 70 eV of energy. The ionization process in general is nothing more than transfer of energy to the neutral molecule in the vapor state, giving the neutral molecule sufficient energy to eject one of its own electrons and thereby become charged with a residual positive charge. This process produces a molecular ion with a positive charge as represented by M+·. The molecule ion or molecular ion still has considerable excess energy, and much of that energy can be dissipated by fragmentation of its chemical bonds. The decomposition of various chemical bonds leads to the production of fragment ions whose mass is equal to the sum of atomic masses of the group of atoms retaining the positive charge during the decomposition process. It is important to realize at this stage that not all of the molecular ions decompose into fragment ions. In molecules producing a molecular ion that is stable, many of them tend to survive, or not fragment, and an intense molecular ion will be recorded. During analysis of a compound having a molecular ion that is unstable, nearly all of the molecular ions decompose into fragment ions, and in these cases, the mass spectrum contains only a small peak for the molecular ion.
Molecular Characterization of Diesel Fuels Using Modern Analytical Techniques
Published in Chunshan Song, Chang S. Hsu, Isao Mochida, Chemistry of Diesel Fuels, 2020
C. S. Hsu, G. J. Dechert, D. J. Abbott, M. W. Genowitz, R. Barbour
Mass spectrometry is well suited for characterizing individual components based on their molecular ions or characteristic fragment ions. Generally, the distributions of thousands of diesel components are grouped into compound types, according to the number of rings and double bonds in the molecules. A commonly used reference method for determining diesel component distribution according to hydrocarbon type is the ASTM D 2425 standard method, utilizing high-voltage EI low-resolution mass spectrometry (EI-MS).10 Due to the presence of isobaric ions (ions with the same mass) in saturated and aromatic hydrocarbons, this ASTM method usually requires a prior separation of the fuel into saturated and aromatic fractions.13 Once the fuel is separated into these two fractions, other ASTM methods can also be used. It is common to analyze saturates by ASTM D 2786 and aromatics by ASTM D 3239, although these two methods were developed for higher boiling gas oil fractions.10
Pyrolysis Gas Chromatography and Mass Spectrometry
Published in Rui Yang, Analytical Methods for Polymer Characterization, 2018
The mass of the molecular ion corresponds to the molecular weight of the compound. The intensity of the molecular ion depends on its stability. For compounds such as aromatics or compounds with a conjugated structure, the intensity of the molecular ion peak is high. For compounds containing -OH, -NH2, and other groups (e.g., O, N, P, and S) or with substituents, the molecular ion peak is weak or even disappears. The order of the peak intensities of the molecular ion is as follows: Aromatics>conjugated alkenes>alkenes>cyclic compounds>carbonyl compounds>linear alkanes>ethers>esters>amines>acids>alcohols>highly branched alkanes.
Selective optical sensing of iron(III) ions in an aqueous medium by benzochromone-based Schiff base and its application on test strips
Published in Environmental Technology, 2022
Shahad Ayed Alahmady, Syed Nazreen, Ali Q. Alorabi, Ahmed A. Elhenawy
The binding stoichiometry was estimated based on Job’s plot, via a continuous variation method, and further confirmed by a spectrophotometric titration method. The results of both methods supported a 1:2 metal–ligand molar ratio, as shown in Figure4a. The maximum coordination according to Job’s method was found approximately at [Fe3+]/([Fe3+] + [HL]) of 0.31, and the equivalent [HL] upon titration method was 2, indicating a 1:2 metal–ligand ratio as well. The possible structure of the complex is depicted in Figure 1b. The complex structure as Fe(III)–2L is reasonably acceptable because HL combined with three functional groups namely carboxyl, azomethine, and chromene-carbonyl, are readily available for coordination with metal, thus suggesting a tridentate ligand and [Fe(III)L2]Cl complex structure. The structure of the complex was also confirmed from mass spectrometry, which displayed a molecular ion peak at 740.17 [M + H]+ as shown in Figure S2. Therefore, these conclusions confirmed the binding of Fe(III) to the HL.
Isolation and identification of 1,3,6,8-tetrabromocarbazole – degrading bacteria
Published in Journal of Environmental Science and Health, Part A, 2022
Shaorong Huang, Suiqiong Sheng, Meixian Bei, Yangyong Zhao, Ruihong Chen
The major metabolites were detected by GC-MS analysis during 1,3,6,8-TBCZ biodegradation. The degradation products were identified by GC-MS based on mass spectral data and Wiley275 mass spectrometry database. The CI (Chemical Ionization) and EI (electron impact ionization) mass spectrometry detected different products respectively. Four major peaks of derivatized samples were found and the molecular ion was at m/z 245.0, 325 and 402.9 respectively, via CI mass spectrometry (Figure 5a). The m/z of the compound B and C was same. Compound A, C and D were identified as bromocarbazole, 3,6-Dibromocarbazole 1,3,6-Tribromocarbazole based on mass spectral data and Wiley275 mass spectrometry database. The compound B was tentatively identified as an isomer of 3,6-dibromocarbazole, but the structure is uncertain. Most of the non-polar products were detected at 33.6 min with m/z 69.2 by GC-MS (EI), but the structural formula couldn’t be determined. (Figure 5b). The possible degradation pathways of 1,3,6,8-TBCZ were proposed based on the identified metabolites and the existing reports on the metabolism of carbazole and dibenzofuran[11–14] (Figure 6).
An efficient synthesis of novel spiro[indole-3,8′-pyrano[2,3-d][1,3,4]thiadiazolo[3,2-a]pyrimidine derivatives via organobase-catalyzed three-component reaction of malononitrile, isatin and heterocyclic-1,3-diones
Published in Journal of Sulfur Chemistry, 2021
Saedehsadat Hosseini, Abbas Ali Esmaeili, Amir Khojastehnezhad, Behrouz Notash
The chemical structure of all prepared products have been characterized with mass, FT-IR, 1H NMR, 13C NMR, and CHN analysis (see Supporting Information). For example, the 1H NMR spectrum of product (6a) exhibited two doublet and two triplet with four protons for the protons related to isatin ring at δ = 687–7.22, a singlet with two protons for NH2 at δ = 7.49, one multiplet (3H) and one doublet (2H) for the protons related to phenyl ring of thiadiazolopyrimidine moiety at δ = 7.60–792, and finally a singlet with one proton for NH at δ = 10.66. Moreover, the FT-IR was another analysis to approve the structures of all synthesized products. In this regard, the IR absorption peak at 3429 cm-1 is assigned to the NH group, the peak at 2197 cm-1 is belongs to CN moiety and the peaks at 1723 and 1698 are attributed to the C=O functional groups. In addition, the carbon NMR spectrum of 6a showed 20 distinct C NMR signal particularly carbonyls at δ = 158.9 and 177.8 ppm and cyanide at δ = 117.8 ppm. Besides, the mass spectrometry of all synthesized compounds exhibited the molecular ion peaks at relevant m/z values.