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Spectroscopy
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
A mass spectrometer is an instrument that bombards an organic molecule (or any other molecule) with high energy electrons to ionize the molecule. Such bombardment usually generates a radical cation although other ions can also be produced under the proper conditions. Usually, an initially formed high-energy radical cation fragments into other (smaller) mass radical cations. An electric field accelerates and focuses the ions toward a large magnet, which separates the radical cations that are produced according to their mass and charge. The ions then pass into a detector, where they are recorded. The recorded collection of ions arranged by their mass is known as the mass spectrum for a molecule. How many kilocalories (kcal) correlate with one electron volt (eV)?
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
Mass spectrometric detection mainly uses electron multipliers, and some use photomultiplier tubes. The ions from the quadrupole strike the high-energy dynodes to generate electrons. The electrons generate electrical signals through the electron multiplier. The signals of different ions are recorded to obtain the mass spectrum. The gain of the signal is related to the voltage of the multiplier. Increasing the voltage of the multiplier can increase the sensitivity, but at the same time, it will reduce the life of the multiplier. Therefore, the multiplier voltage should be as low as possible while ensuring the sensitivity of the instrument. The electrical signals from the multiplier are sent to the computer for storage. These signals can be then processed to obtain chromatograms, mass spectra, and other information.
Measurement of Pressure
Published in Pramod K. Naik, Vacuum, 2018
Terms, commonly used in mass spectrometry are discussed. Scanning: The variation of the parameters such as magnetic field or ion accelerating voltage in the case of magnetic sector type mass spectrometers and the variation of RF and DC voltages in quadrupole analyzers that causes the ions of different m/e ratios to be collected at the detector is called scanning. Mass spectrum: The mass spectrum is a plot representing the distribution of detected ions. The masses of ions (the masses divided by their charge) appear on the x axis. The charge on the ion is assumed as 1+. Figure 5.28 shows a typical mass spectrum indicating the variation of ion current at the collector resulting from scanning. Ions of a particular m/e ratio correspond to the value of the parameter varied during the scanning. Thus the peaks in the spectrum can be identified with the particular mass numbers. The magnitudes of the partial pressures correspond to the heights of the individual peaks. The abundance is expressed
Antiepileptic drugs in aquatic environments: Occurrence, toxicity, transformation mechanisms and fate
Published in Critical Reviews in Environmental Science and Technology, 2023
Quanzhen Liu, Long Wang, Xiong Xu, Saihong Yan, Jinmiao Zha, Donghong Wang, Dan Zhu
It is worth noting that AEDs and their metabolites/transformation products should be analyzed by different operation modes of LC–MS according to analysis strategies. For quantification of drugs, the most common mode operation is monitoring reaction multiple (MRM) of target analysis. The relevant standards in this mode are required to optimize compound-specific MS conditions including fragment-ion masses, ion-source voltages and collision energy (Acena et al., 2015). And environmental concentrations can be defined according to standard curve. As for the identification of unknown products, the operation modes of suspect and nontargeted screening will be recommended. The modes need to acquire mass spectrum information, retention time and isotope pattern by UPLC-high resolution mass spectrometry (UPLC-HRMS), then match the existing mass spectrum library such as MassBank, mzCloud, and so on, and finally define the compounds with the highest similarity of mass spectrum (Du et al., 2022). In previous study, twenty-two transformation products of CBZ have been found by nontarget analysis during chlorination and five of those were first reported (Han et al., 2018). However, specific structures of partial transformation products with two isomers such as chlorinated acridone (Cl-acridone) have not been identified limited to the current mass spectrometry analysis methods, which is also a challenge for nontarget analysis.
Vanadium(IV) coordination complexes with excellent biological activities: a synthetic, characterization, and density functional theory approach
Published in Journal of Coordination Chemistry, 2022
Sonika Sharma, Debasish Das, Biswajit Sadhu, Neeraj Sharma
All complexes were synthesized using analytical grade chemicals purchased from Merck, India. A reported method [33] was used for the synthesis of potassium 4-nitrocinnamohydroxamate ligand. Gravimetric method was used to determine the vanadium content in complex as V2O5 and elemental analyses were carried out on a Carlo-Erba 1108 analyzer. The molar conductance of the complexes was measured using an Elico Conductivity Bridge type CM-82T. FTIR spectra of the complexes were recorded on a Nicolet-5700 FTIR spectrophotometer (range 4000–200 cm−1) using KBr pellets. Gouy’s method was used to determine room temperature magnetic susceptibility using Hg[Co(NCS)4] as calibrant. UV–vis spectrum was recorded on a Varian Cary100 Bio UV–vis spectrophotometer using methanol as a solvent. The electron spray ionization mass spectrometry (ESI-MS) technique was used for recording mass spectrum of 1. The electrochemical experiment was performed in MeOH:H2O (95:5) medium using Bu4NClO4 as supporting electrolyte. Electrodes set up consist of three-electrode system comprising of Pt-disk working electrode, Pt-wire as auxiliary electrode and an Ag/AgCl electrode as reference electrode in a single compartmental cell of volume 10–15 mL. Thermal studies of 1 were done at a heating rate of 10 °C min−1 under nitrogen atmosphere on an EXSTAR TG/DTA 6300 thermal analyzer.
Analysis of newly synthesized disulfides of aryldithiocarbonates and vanadium(V) and niobium(V) complexes of aryldithiocarbonates based on spectroscopic, thermogravimetric, SEM and DFT studies
Published in Molecular Physics, 2020
Savit Andotra, Atiya Syed, Sandeep Kumar, Mandeep Kour, Sushil K. Pandey
Mass spectroscopy is one of the most important methods to determine molecular weight of the complexes and to identify the fragments formed during bombardment, which reveals composition and properties of the particular moiety of the complexes. The mass spectra of oxovanadium(V) complexes (5, 8) and niobium complexes (9, 12) have shown the presence of molecular ion peak [M+] at 468.9 (5), 537.8 (8), 565.8 (9) and 634.6 (12). Two significant peaks that were observed in the mass spectrum are the molecular ion peak, indicating the molecular mass of the complex, which is very weak in case of the complexes investigated and the base peak, corresponding to the fragment CH3C6H4O+. The various fragments observed are agreement with the molecular formula of the complexes. The occurrence of molecular ion peak [M+] is supporting the monomeric nature of the complexes. Moreover, the complexes containing the chlorine atom (8, 12) displayed the appearance of isotopic peaks in the mass spectrum. The masses of the fragmented ion listed in the table are calculated using one chlorine atom mass equal to 35 amu as it is the most abundant isotope of chlorine atom. The overlap of these isotope patterns occurs in the mass spectrum.