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Analysis of Clinical Specimens Using Inductively Coupled Plasma Mass Spectrometry
Published in Steven H. Y. Wong, Iraving Sunshine, Handbook of Analytical Therapeutic Drug Monitoring and Toxicology, 2017
K. Owen Ash, Gabor Komaromy-Hiller
Ions are injected from the source along the axis of the quadrupole ion trap. The charged particles are under the influence of the quadrupole field that forces them to oscillate along the central axis of travel. Depending on their m/z ratio, ions display different trajectories. Some of these trajectories are unstable (i.e., they tend toward infinite displacement from the center of the traveling axis). These ions are lost and not detected (e.g., through collision with an electrode). Ions that are successfully transmitted through the analyzer are said to possess stable trajectories. These ions give rise to a signal in the detection system. The path stability of an ion depends on the radiofrequency (Ω), and the magnitude of the dc and radiofrequency potentials (U and V).22 The ratio of the dc and radiofrequency potentials (U/V) determines the resolution of the instrument. At zero dc potential (U = 0), wide bands of m/z values are transmitted; but, as the ratio U/V increases, the resolution of a single m/z value also increases. A mass spectrum can be generated in two ways: either by scanning U and V while keeping their ratio, as well as the radiofrequency constant, or by scanning the frequency and holding U and V constant.
Detection of Food Allergen Residues by Immunoassays and Mass Spectrometry
Published in Andreas L. Lopata, Food Allergy, 2017
Sridevi Muralidharan, Yiqing Zhao, Steve L. Taylor, Nanju A. Lee
All MS instruments measure ions by their mass-to-charge (m/z) ratios. Ion motion is regulated by electric and magnetic fields under vacuum. MALDI and ESI ionisation interfaces allow easy coupling with different mass analysers. Mass analysers types widely in use include quadrupoles (Q), linear ion-trap, quadrupole ion-trap, Orbitrap, time of flight TOF and Fourier-Transform Ion Cyclotron Resonance (FTICR) mass analysers. Multiple stage mass analysers such as triple quadrupole (QQQ), tandem TOF (TOF/TOF) or hybrid Q/TOF instruments are already popular for their increased accuracy and resolution. As extensively reviewed, different mass analysers show slightly varying sensitivity, resolution and mass accuracy in their MS/MS spectra and this is attributed to their technical improvements (Picariello et al. 2011, Rubert et al. 2015). Ion traps are sensitive and have high dynamic range but were limited to moderate mass accuracy and relative quantification but recent orbitrap and fourier transform (FT) instruments have shown excellent sensitivity and mass accuracy (Scigelova and Makarov 2006). Ion traps are capable of multi stage MSn, useful for peptide characterisation, are sensitive and, whereas TOFs show high mass range but moderate resolution, and are suited for absolute quantification. Factors such as sensitivity and specificity (high resolution) are characteristic of the MS instrument being used and need to be chosen to fit for purpose. LC-ESI-MS/MS, MALDI-TOF TOF and QQQ instruments are predominant choices among the food allergen scientific community and have been used from identification to detection and quantification of food allergenic proteins and peptides from complex matrices (Johnson et al. 2011, Koeberl et al. 2014).
Adulteration of Essential Oils
Published in K. Hüsnü Can Başer, Gerhard Buchbauer, Handbook of Essential Oils, 2020
However, fingerprinting of EOs by GC with FID detection alone cannot reveal the chemical identity of detected peaks if any deviations from the expected profiles occur. In that case further information is needed besides the chromatographic data, and mass spectrometry provides detailed information on the structure of the separated compounds. High-resolution gas chromatography coupled with a mass spectrometric detector (HRGC-MS or simply GC-MS), most commonly quadrupole ion trap detectors in EO analysis, together with sophisticated chromatographic software and special mass spectral libraries of essential oil components (Königet al., 2004; Adams, 2007; Mondello, 2011) separates and identifies most components of an EO. Since some classes of compounds show very similar mass spectra, like some groups of mono- and sesquiterpenes, retention indices must be taken into account as a second criterion for an unequivocal identification. Usually a GC-MS run is performed for identifying the EO components and a second GC-FID run for peak area, respectively, for percentage composition determination. Normally this is done on two different instruments. Identical capillary columns must be used in both GCs, and device parameters must be adjusted properly to obtain closely similar chromatographic profiles for both detectors to facilitate peak allocation between the two chromatograms. Peaks identified in the mass spectrometry (MS) chromatogram must be correctly assigned in the FID chromatogram for peak integration. Sometimes this is proving difficult since separation on two instruments is never exactly equal especially if one column ends up in a high vacuum (MS) and the other at atmospheric pressure (FID). Therefore, a series of closely eluting peaks may not be resolved in the same manner on both columns. To overcome this problem, an FID-MS splitter can be used since here the separation takes place on one GC column and the effluent is split to both detectors, MS and FID. To detect peak overlapping, the same procedure should be undertaken on another capillary column of different polarity. In EO analysis GC separations are preferably performed on 95% dimethylpolysiloxane/5% diphenylpolysiloxane and on Carbowax 20 M columns. In the end you come up with two FID and two MS chromatograms, each of the two carried on different capillary columns. These results in two analyses that should for the most part coincide and accept the overlapping peaks on the other GC column. EO analysis performed in this way confirms the chemical composition of an EO and detects adulterations with exogenic substances if they are amenable by GC, that is, volatile. Adulterations with gas chromatographic undetectable substances like very high boiling vegetable or mineral oils can be disclosed by a change in the percentage composition or a too low total peak area. Specific marker compounds or a diastereomeric isomer distribution can also be used for authentication of EO (Teisseire, 1987).
Liquid chromatography coupled to mass spectrometry for metabolite profiling in the field of drug discovery
Published in Expert Opinion on Drug Discovery, 2019
Javier Saurina, Sonia Sentellas
Strategies for metabolite identification by MS have been changed along the years in parallel to the rapid evolution of the technology [68]. Nowadays, high resolution instruments, able to distinguish peaks of compounds with highly similar mass-to-charge (m/z) values, are gaining popularity against the oldest and well known counterparts such as ion trap (IT), TQ or hybrid quadrupole-ion trap (QTRAP) platforms. Spectral analysis from MS and MS/MS as well as ‘more complex’ detection modes, such as neutral loss (NL) and precursor ion (PI) scans using TQ or MSn fragmentation using IT, have been extensively employed for the detection of unknown metabolites. Often, combinations of different platforms are needed in order to have more comprehensive information. In addition, the use of deuterated solvents (with low or high resolution MS) has also demonstrated its ability to carry out metabolite identification based on H/D exchange [72,73]. A more thorough description of the aforementioned platforms is given elsewhere [5,7,70,71].
Covalent labeling and mass spectrometry reveal subtle higher order structural changes for antibody therapeutics
Published in mAbs, 2019
Patanachai Limpikirati, John E. Hale, Mark Hazelbaker, Yongbo Huang, Zhiguang Jia, Mahdieh Yazdani, Eric M. Graban, Robert C. Vaughan, Richard W. Vachet
Mass spectra were acquired on a Thermo Scientific Orbitrap Fusion mass spectrometer. The nano-electrospray ionization source was operated in the positive mode using a needle voltage of 2,000 V. The ion transfer tube temperature was set to 300°C. The resolution of Orbitrap was set to 60,000 and the MS1 AGC target and maximum injection time were optimized and set to 1 × 106 ions and 100 msec, respectively. Tandem mass spectrometry (MS/MS) was performed on linear quadrupole ion trap for the most abundant peptide ions, with ion abundances above 5,000. The precursor ions were selected using a quadrupole mass filter at an isolation width of 2.0, and the MS2 AGC target and maximum injection time were set to 5 × 104 ions and 100 msec, respectively. Tandem mass spectra were generated using collisional-induced dissociation with a normalized collision energy of 35%. To avoid a biased selection of high-abundance ions, a dynamic exclusion of 60 sec was activated after 5 spectra were acquired for any given precursor ion within 5 sec. Mass detection during MS and MS/MS was done in centroid mode to ease the data analysis.
Quantifying RNA modifications by mass spectrometry: a novel source of biomarkers in oncology
Published in Critical Reviews in Clinical Laboratory Sciences, 2022
Amandine Amalric, Amandine Bastide, Aurore Attina, Armelle Choquet, Jerome Vialaret, Sylvain Lehmann, Alexandre David, Christophe Hirtz
MS was first applied to epitranscriptomics at the end of the last century [66]. Since then, different mass spectrometers have been used to quantify nucleosides in body fluids. They have either a single analyzer, such as with quadrupole ion trap (QTRAP) or two analyzers, as in quadrupole time-of-flight (QTOF) and triple quadrupole (QQQ) machines. At present, QTOF is employed simultaneously for targeted and un-targeted molecules whereas QQQ is used for the quantification of compounds with known molecular mass. As a consequence, QQQ is most used in the clinical laboratory due to its higher sensitivity, rapid targeting capabilities and simpler data analysis [66,67].