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Coupled Mass Spectrometic—Chromatographic Systems
Published in Steven H. Y. Wong, Iraving Sunshine, Handbook of Analytical Therapeutic Drug Monitoring and Toxicology, 2017
The advantage of APCI to the toxicologist lies in the area of ionization of neutral molecules, such as steroids and relatively polar, low-molecular weight species. For these molecules, APCI produces mainly protonated molecular ions that can be monitored directly or fragmented either in the interface region or in a collision cell (SRM). The majority of applications of APCI have been for selective quantitative analysis, because there are no libraries available for matching MS/MS spectra, nor are there clearly delineated rules for interpretation that exist for electron ionization (EI). Henion et al.36 described a robust “heated pneumatic nebulizer” that allowed direct coupling of standard HPLC columns to a mass spectrometer. A co-axial stream of air assists in the nebulization of the the HPLC effluent, and the solvent is removed during passage through a large diameter, heated quartz tube. The ions are transported through the interface region (Figure 10–6), wherein declustering of the solvent molecules occurs, and into the mass spectrometer. This approach has been used routinely for analysis of hundreds of samples per day in the pharmaceutical industry for pharmacokinetic studies and metabolite identification. APCI is a useful adjunct to electrospray (ES) ionization for addressing a wide spectrum of problems.
Metabolomics of Microbial Biofilms
Published in Chaminda Jayampath Seneviratne, Microbial Biofilms, 2017
Tanujaa Suriyanarayanan, Chaminda Jayampath Seneviratne, Wei Ling Ng, Shruti Pavagadhi, Sanjay Swarup
In APCI, the analyte liquid is pumped through a capillary and nebulised at the tip. A corona discharge located near the tip of the capillary is used to ionise the gas and solvent molecules present in the ion source. The analyte samples react with the ions generated and become ionised in turn by means of charge transfer. APCI is a particularly useful technique for ionising small thermally stable molecules that are not effectively ionised by ESI. Moderately polar metabolites, such as fatty acids and steroids, are suitable for ionisation through APCI mode. It has been reported that APCI mode is more sensitive than ESI mode for detection of phospholipids, especially phosphoethanolamines [69]. Another distinction from ESI is that multiple charging does not occur and so singly charged ions dominate [70].
Metabolomic Techniques to Discover Food Biomarkers
Published in Dale A. Schoeller, Margriet S. Westerterp-Plantenga, Advances in the Assessment of Dietary Intake, 2017
Pekka Keski-Rahkonen, Joseph A. Rothwell, Augustin Scalbert
Interfacing of the LC system to MS is made through an ion source, which is used to evaporate the sample and ionize the dissolved molecules for their detection as ions. Different ion sources are available which will cause major differences in metabolite coverage. Most published metabolomics methods have been based on electrospray ionization (ESI), which is most suitable for the analysis of compounds that are ionizable in solution. ESI is a soft ionization technique that does not induce excessive fragmentation of chemically labile compounds, but is somewhat susceptible to coeluting matrix interferences from the biological background. Matrix effects, such as ion suppression, can mask the concentration–response relationship or render a compound undetectable. Alternative ion sources such as atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) are available, which both enable more efficient ionization of neutral compounds and suffer less from matrix effects, although with less efficient ionization of highly polar metabolites and more in-source fragmentation. The potential benefits of APCI and APPI in metabolomics have been well recognized, but they have remained less commonly used (Ernst et al. 2014; Mirnaghi and Caudy 2014). Irrespective of the ion source type, an important parameter is the ionization mode used to create the ions. Depending on the molecular structure, it may be possible to detect a metabolite only as a cation or an anion, and it is thus advantageous to perform sample analyses with both polarities. In addition to ion sources, a promising new technology for LC–MS metabolomics is ion mobility MS. This is achieved with a hybrid instrument where the ions generated in the ion source are taken into a gas-phase separation system before mass analysis. This enables measuring the drift time for the ions, which is analogous to LC retention time, and can add another dimension to the data that can increase the number of selectively detected compounds (Dwivedi et al. 2010; May et al. 2015). One challenge of the technique lies in the processing of the acquired data, which require software that can fully exploit the additional drift time measurements.
Gastric protective effect of Alpinia officinarum flavonoids: mediating TLR4/NF-κB and TRPV1 signalling pathways and gastric mucosal healing
Published in Pharmaceutical Biology, 2023
Kaiwen Lin, Tang Deng, Huijuan Qu, Hongya Ou, Qifeng Huang, Bingmiao Gao, Xiaoliang Li, Na Wei
In October 2017, the rhizome of A. officinarum was collected (Haikou city, Hainan Province, China) and identified by Professor Zeng Niankai (Hainan Medical University). Some samples were stored in the Laboratory of Natural Phytomedicinal Chemistry of Hainan Medical University (specimen number: 20171024). Subsequently, the composition and structure of flavonoid compounds were extracted and analysed using laboratory-validated extraction methods (a kilo of A. officinarum was refluxed with 80% ethanol for 1 h and concentrated to 40% under reduced pressure. Then, the extract was purified with AB-8 macroporous. The ethanol elution fraction was subjected to silica gel column chromatography and eluted with a petroleum ether-ethyl acetate gradient. The fractions were subjected to gel column chromatography and eluted with methanol to obtain F.AOH), ultra-high performance liquid chromatography diode array detector, and mass spectrometer analysis (the ultra-high performance liquid chromatography-diode array detector-mass spectrometry (UHPLC-DAD-MS) data were obtained from an Agilent 1290 Infinity series UHPLC system with a diode array detector and an Agilent 6120 quadrupole mass spectrometer. The mass spectrometer contained a dual atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) interface.) (Lin et al. 2020), and flavonoids were then stored in the refrigerator at −20 °C for subsequent analysis.
Mass spectrometry based metabolomics for small molecule metabolites mining and confirmation as potential biomarkers for schistosomiasis – case of the Okavango Delta communities in Botswana
Published in Expert Review of Proteomics, 2022
Sedireng M. Ndolo, Matshediso Zachariah, Lebotse Molefi, Nthabiseng Phaladze, Kwenga F. Sichilongo
Table 1 summarizes the instrumentation, methods, ionization modes, columns, data filtration, and statistical evaluation techniques that have been employed in schistosomiasis metabolomics involving separation science and mass spectrometry for small molecules. Table 1 also emphasizes that there is very little literature on the metabolomics of schistosomiasis using either LC-MS or GC-MS. This underscores the tag attached to this disease, i.e. ‘a neglected tropical disease,’ which is the case despite affecting over a quarter of a billion people globally. The most commonly used ionization mode is electrospray ionization (ESI) for LC-MS and electron ionization (EI) for GC-MS. Future studies could focus on interrogating other ionization techniques, such as atmospheric pressure chemical ionization (APCI). This is well suited for small-molecule ionization using LC-MS and soft ionization, such as field desorption, in addition to chemical ionization for GC-MS. These techniques need to be probed for the analysis of abundant metabolites during ionization. There is a need to explore other data filtration software packages, in addition to XCMS, in order to increase the chances of biomarker discovery. This applies to multivariate statistical tools that revolve around PCA and PLS-DA.
A sensitive and high-throughput LC-ESI-MS/MS method to detect budesonide in human plasma: application to an evaluation of pharmacokinetics of budesonide intranasal formulations with and without charcoal-block in healthy volunteers
Published in Drug Development and Industrial Pharmacy, 2021
Xin Li, Huan Tong, Bing Xu, Yang Deng, Yuan Li, Junchen Huang, Yong Mao, Mengqin Liu, Ping Zhang, Siwei Guo
LC-MS/MS is the most used method for detecting budesonide. It is obvious that a low level of matrix suppression about 10–30% consistently exists when using the ESI source [17,21]. This may be caused by the co-elution of endogenous substances such as phospholipids and cholesterol. Even though Nilsson et al. [22] tried to use a phospholipid removal plate to remove most of the phospholipids, they still observed ion suppression, resulting in a low recovery. The atmospheric pressure chemical ionization (APCI) or atmospheric pressure photoionization (APPI) source seems to slightly less liable to MF than ESI source. [19,24] In addition, the application of co-eluting isotopically labeled IS could be an effective alternative strategy to offset the suppression of matrix. [19] In our study, nearly 20% matrix suppression was observed, which was consistent at different plasma levels. When normalized by isotopically labeled IS, the MF, as measured by their CV (%), was lower than 4.1%.