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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
Combined GC/MS provides three-dimensional data for each component: GC retention time (correlated with boiling point if the GC column is coated with a nonpolar stationary phase, such as methyl silicone), mass (molecular and fragment), and abundance. The mass spectra acquired can be used as fingerprints for compound identification. Electron ionization (EI) commonly provides molecular weight and structural information, although other ionization techniques, such as chemical ionization, are often used to confirm molecular weight and molecular type. In GC/MS, the distribution of diesel components can be displayed by mass chromatograms -- ion-current traces of selected masses as a function of GC retention time. Figures 2–2 and 2–3 show mass chromatograms of a homologous series of 98 daltons (Da) ions for a severely hydrotreated diesel fuel (Diesel A) and a typical diesel fuel (Diesel B), respectively. A reconstructed (or total) ion chromatogram (RIC, total ion current as a function of GC retention time and equivalent to a GC trace with flame ionization detection) is also shown as a bottom trace in each figure for reference.
Analysis of Pesticide Residues by Chromatographic Techniques Coupled with Mass Spectrometry
Published in José L. Tadeo, Analysis of Pesticides in Food and Environmental Samples, 2019
Wan Jing, Jin Maojun, Jae-Han Shim, A.M. Abd El-Aty
Electron ionization (EI) is the most widely used ion source. It is mainly used for ionization of volatile organic samples. The sample is injected as a gas into the ion source. The sample molecules are ionized by colliding with the electrons emitted from the filament. The organic molecules may then form molecular ions. They may also form fragment ions, as chemical bonds may break down. The molecular weight of any compound can be validated from the molecular ion and its structure can be obtained from the fragment ions. The ionization potential of general organic compounds is approximately 10 eV, while the ionization energy commonly used for EI is 70 eV. Thus, sample molecules are ionized to molecular ions and further fragmented to produce abundant fragment ions under such high energy. EI is therefore called a “hard ionization” technology.
Breathomics and its Application for Disease Diagnosis: A Review of Analytical Techniques and Approaches
Published in Raquel Cumeras, Xavier Correig, Volatile organic compound analysis in biomedical diagnosis applications, 2018
David J. Beale, Oliver A. H. Jones, Avinash V. Karpe, Ding Y. Oh, Iain R. White, Konstantinos A. Kouremenos, Enzo A. Palombo
As the name suggests, samples for GC-MS must either be in the gaseous phase or, more likely, be transferred into the gaseous phase by heating. The sample is then injected into the chromatograph where an inert carrier gas (usually helium, but increasingly hydrogen) is used to transport it through a packed or open, tubular (capillary) column. The column is typically coiled and very thin (0.25 mm internal diameter) allowing even those tens of meters in length to be housed within a relatively small temperature controlled oven. The exact length of the column depends on the type and speed of the desired analysis, but for metabolomic studies, longer columns (∼30 meters) are generally used as these provide better chromatographic resolution and ensure maximum separation of the analytes in complex samples. Separation of compounds occurs due to differing rates of partitioning of the components of the sample between the internal lining of the column (stationary phase) and the carrier gas (mobile phase). This means each compound exits the column at a different time (known as the retention time). The mass spectrometer (MS) can then be used to detect eluting compounds, traditionally using electron impact (EI) ionization to ionize the compound, and then to measure the mass to charge ratio of each ion and generate a unique mass spectrum for the compound. SPME can also be used to absorb and pre-concentrate volatile compounds in breath prior to analysis.
Enhancement of Fenton processes at initial circumneutral pH for the degradation of norfloxacin with Fe@Fe2O3 core-shell nanomaterials
Published in Environmental Technology, 2019
Jingyi Liu, Wenyong Hu, Maogui Sun, Ouyang Xiong, Haibin Yu, Haopeng Feng, Xuan Wu, Lin Tang, Yaoyu Zhou
According to our previous work, the concentration of NOR was analyzed using an ultraviolet spectrophotometer in an aqueous solution with a maximum absorption wavelength of 273 nm [9]. The measurement of iron content by 1,10-phenanthroline colouring method has the advantages of high sensitivity, simple operation, fast and stable colour. In the solution of pH 3.0–9.0, Fe2+ and 1,10-phenanthroline completed to form a stable orange-red complex , the maximum absorption wavelength was 510 nm of this orange-red complex, and iron content in the range of 0.1–6 μg/mL to comply with Bill’s law. By making the standard curve of Fe2+ concentration and absorbance, we can measure the Fe2+ concentration with an ultraviolet spectrophotometer. The exact content of H2O2 in the reaction solution at different times was determined as much as possible. We use the Ce(SO4)2 method to determine the content of H2O2. The method is a 4-valent cerium salt solution as a titrant for capacity analysis. The method is simple and easy to operate. Under the condition of rare earth acid such as dilute H2SO4 or dilute HCl, titration of H2O2 with Ce(SO4)2 standard solution with FeSO4 and 1,10-phenanthroline as the indicator is very suitable in the process of reaction, the residual H2O2 content and the precision of the reaction solution were measured in time and accurately. The material was characterized by scanning electron microscopy (SEM). The structure and properties of the materials were measured by Fourier transform infrared spectroscopy (FTIR). The intermediates were identified by gas chromatography-mass spectrometry (GC-MS) equipped with a TG-5 column (30mϕ × 0.25 mm ID, 0.25 μm film thickness). Electron bombardment (EI) is used as an ionization technique with an electron energy of 70 eV. Using helium as the carrier gas at a constant flow rate of 1.0 mL/min. The sample volume was 10 μL.