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Mass Spectrometric Analysis
Published in Adorjan Aszalos, Modern Analysis of Antibiotics, 2020
The electrohydrodynamic spectra were taken with a double-focusing mass spectrometer (AEI MS-902). The voltage applied to the specially prepared platinum capillary needle emitter (0.2 mm) was about +8.6 kV. The collecter cup was at ground potential, and the ion current was measured with either an electrometer or an oscilloscope. The mass spectrometer was operated at a resolution of 800 and the electron multiplier set between 3000 and 500,000 V with a 50 Hz bandwidth for the amplifier. Spectra were obtained from 950 to 10 m/z at a rate of 160 sec per decade with an oscillographic recorder.
Emerging Biomedical Analysis
Published in Lawrence S. Chan, William C. Tang, Engineering-Medicine, 2019
In quadrupole, IT and TOF instruments, electron multiplier and microchannel plates are used as detectors. The electron multiplier was designed by extending the principles of the Faraday cup. It utilizes either multiple dynodes or a horn-shaped continuous dynode to amplify the electric signal and improve the sensitivity of detection. Microchannel plates are compact electron multipliers. Typically, the diameter of each channel is around 10 micrometers, and a microchannel plate usually consists of 10,000 to 10,000,000 closely packed channels (Wiza 1979). This design allows microchannel plates to provide additional spatial resolution.
Dictionary
Published in Mario P. Iturralde, Dictionary and Handbook of Nuclear Medicine and Clinical Imaging, 1990
Detector noise. Continuous background of very small, random pulses or noise produced by a nuclear detector in the absence of any incident particles. This occurs, for example, in the use of scintillation detectors in which the light produced by the scintillator releases photoelectrons from the sensitive cathode or an electron multiplier which multiplies the signal so that an output pulse of several volts may be produced. Inevitably thermal agitation also releases electrons from the various sensitive surfaces, and these are also multiplied to produce a continuous background of small pulses, or noise, at the output stage. This detector noise can be reduced by cooling the photomultiplier tube. The level of the noise sets a lower limit to the energy of the radiation which can be studied with a scintillation spectrometer.
Amorphization and modified release of ibuprofen by post-synthetic and solvent-free loading into tailored silica aerogels
Published in Drug Delivery, 2022
Ajmal Zarinwall, Viktor Maurer, Jennifer Pierick, Victor Marcus Oldhues, Julian Cedric Porsiel, Jan Henrik Finke, Georg Garnweitner
To elucidate the coordination mode of the ligands, thermogravimetric analysis (TGA; STA7200, Hitachi High-Tech Analytical Science, Oxford, UK) was linked with mass spectrometry (GSD 320 Thermostar TM, Pfeiffer-Vacuum, Asslar, Germany) via a coupling device (280 °C, REDshift, San Giorgio in Bosco, Italy). 10–12 mg of the samples were measured in alumina crucibles at a heating rate of 10 K/min in a nitrogen flow of about 200 mL/min up to 600 °C. The flow was redirected into a heated transfer capillary (deactivated fused silica tubing; inner diameter: 0.15 mm; outer diameter: 0.22 mm; kept at 280 °C; split of 1:200) and the coupling into the inlet (150 °C) of the mass spectrometer. The mass spectrometer was operated in the electron ionization mode at 70 eV with a secondary electron multiplier at 1080 V as detector. Measurements were performed in multiple-ion detection mode (MID) with 200 ms measurement time. The measured ion currents I(T) were baseline-corrected to their minimum Imin and normalized to the weight of the sample msample to obtain comparable ion currents Irel(T) according to:
Analyzing pesticides and metal(loid)s in imported tobacco to Saudi Arabia and risk assessment of inhalation exposure to certain metals
Published in Inhalation Toxicology, 2022
Mohammed A. Al Mutairi, Hatim A. Al Herbish, Rakan S. Al-Ajmi, Hatim Z. Alhazmi, Reham A. Al-Dhelaan, Abdullah M. Alowaifeer
Pesticide residues that were not detected by the LC-MS/MS were detected using a 7890 A gas chromatograph-mass spectrometer (GC-MS/MS) (Agilent, USA) equipped with DB-5MSUI column (5% Phenyl 95% dimethylarylene siloxane, Agilent, USA). Helium gas was used as carrier gas (99.999% purity) at a constant flow rate of 1.0 ml min−1. The sample injections were done using a Gerstel-PAL System Series autosampler. The initial temperature of the column was 70 °C held for 2 min, then ramped to 150 °C at 25 °C min−1, followed by 3 °C min−1 until 200 °C, and then 8 °C min−1 until 280 °C, which was held for 10 min. Samples were injected in a Split/Splitless mode with a 2 μL injection volume, and the run time was 41.27 min. An electron ionization mode was used to run the mass spectrometer using an electron multiplier voltage between 1000 and 2000 V, and a mass selective detector (MSD) was used as a detector. The MS quad temperature was set to 150 °C, and the ion source temperature was set for 280 °C. The mass spectrometer was acquired in the mass range from 50 to 600 amu.
Mass spectrometry in the lipid study of cancer
Published in Expert Review of Proteomics, 2021
Md. Mahamodun Nabi, Md. Al Mamun, Ariful Islam, Md. Mahmudul Hasan, A.S.M. Waliullah, Zinat Tamannaa, Tomohito Sato, Tomoaki Kahyo, Mitsutoshi Setou
The selection of the ionization source is important in MS studies of a particular group of molecules. Numerous ionization sources, including electrospray ionization (ESI) [23], chemical ionization (CI), atmospheric pressure chemical ionization (APCI), atmospheric pressure photo ionization (APPI), matrix-assisted laser desorption ionization (MALDI), desorption electrospray ionization (DESI), and secondary ion sources have been developed that are compatible with a variety of mass analyzers. Recently, rapid evaporative ionization mass spectrometry (REIMS) has emerged as an efficient technique for direct analysis of samples in near real time [24]. Time-of-flight (TOF) is the most widely used mass analyzer because of its high sensitivity and fragmentation capabilities in tandem mass spectrometry (MSn) analysis. Other commonly used analyzers are ion trap and quadrupole time-of-flight (QTOF) [25]. The Fourier-transform ion cyclotron resonance (FT-ICR) mass analyzer offers the best mass resolution and has thus far been applied in MALDI-MS. Usually, mass analyzers generate a current flow for each separated ion which is transformed digitally. The detector measures charged particles and records the abundances of each ion present in a sample. Initially, mass detectors (for example, Faraday Cup) were designed to capture and count the number of charged ions [26]. The commonly used mass detectors in the modern instrument are the secondary electron multiplier and image current. For example, FT-ICR and Orbitrap mass analyzer use image current for ion detection [27].