Atmospheric pressure chemical comparative studies

El-Hela, A.A., Al-Amier, H.A., and Ibrahim, T.A. 2010. Comparative study of the fla-vonoids of some Verbena species cultivated in Egypt by using high-performance liquid chromatography coupled with ultraviolet spectroscopy and atmospheric pressure chemical ionization mass spectrometry. J. Chromatogr. A 1217 6388-6393. 

Atmospheric-pressure chemical ionization (APCI) has been used for analysis of relatively polar lipids in comparison to those analyzed by El and Cl. APCI/MS spectra are relatively simple, with a protonated molecular ion as the most common base peak. Many classes of lipids, including free fatty acids, phospholipids, sterols, and TG, are ionizable by APCI. Although APCI is a relatively soft ionization technique, the comparatively harsh conditions employed relative to electrospray ionization (ESI) still induce some degree of fragmentation. After they were made commercially avaOable in the late 1980s and early 1990s, both ESI and MALDI mass spectrometers were extensively used for analysis of almost all nonvolatile lipids in their intact forms. Summaries for the majority of these studies can be found in multiple valuable review articles. " " ... 

Towards this goal, there have been extensive studies that have compared PTR-MS measurements of atmospheric VOCs with those obtained by other atmospheric analytical techniques, such as GC-MS [17], GC-FID [21-26], atmospheric pressure chemical ionization mass spectrometry (AP-CIMS) [27], differential optical absorption spectroscopy (DOAS) [24,28] and Fourier transform infrared (FTIR) spectroscopy [17,29], in addition to offline sampling methods coupled to GC analysis [30-34], These studies have shown that PTR-MS is capable of accurately measuring concentrations of VOCs providing that there is no contribution to the miz of interest in a mass spectram by interfering species. If other compounds are present in the atmospheric sample which can lead to ions (protonated parent compounds, cluster ions or fragment ion species) at the nominal mJz of the protonated VOC of interest, then the lack of specificity associated with PTR-MS requires that the actual identity of the compound still needs to be confirmed by other analytical techniques, such as GC-MS. 

In thermospray interfaces, the column effluent is rapidly heated in a narrow bore capillary to allow partial evaporation of the solvent. Ionisation occurs by ion-evaporation or solvent-mediated chemical ionisation initiated by electrons from a heated filament or discharge electrode. In the particle beam interface the column effluent is pneumatically nebulised in an atmospheric pressure desolvation chamber this is connected to a momentum separator where the analyte is transferred to the MS ion source and solvent molecules are pumped away. Magi and Ianni (1998) used LC-MS with a particle beam interface for the determination of tributyl tin in the marine environment. Florencio et al. (1997) compared a wide range of mass spectrometry techniques including ICP-MS for the identification of arsenic species in estuarine waters. Applications of HPLC-MS for speciation studies are given in Table 4.3. 

Laboratory (4) and Process Development Unit (5,6) studies originally conducted at the Universite de Sherbrooke, and now conducted jointly with the private industry at Universite Laval, province of Quebec, have led to the conclusion that thermal decomposition under reduced pressure is an attractive approach for the conversion of biomass into chemicals and fuels products. The process uses a multiple-hearth furnace for wood pyrolysis. This approach is characterized by a low pressure and a short residence time of the vapor products in the rciactor. When compared with conventional, atmospheric pressure carbonization, vacuum pyrolysis has the potential to significantly enhance the yields of organic liquid products with respect to solid and gaseous products. The pyrolysis oils (biooils) obtained from this process can be deoxygenated into transportation fuels upon further upgrading (7). Specialty as well as commodity (Pakdel, H. Roy, C. Biomass, in press) chemicals can also be extracted from the pyrolysis oil product. 

The International Journal for Ion Mobility Spectrometry is the official publication of ISIMS and publishes fully peer-reviewed research and application-oriented papers, critical reviews, technical notes, and topical issues. The journal is abstracted or indexed in Chemical Abstracts Service (CAS), Compendex, Google Scholar, Online Computer Library Center (OCLC), SCOPUS, and Summon by Serial Solutions. Articles can include presentations in all aspects of the mobility, reaction chemistry, and behavior of ions in a supporting gaseous atmosphere and in an electrical field. Also included are biomolecular studies, mobility at comparatively low pressure, instrumentation for field and process monitoring, and measurements of samples for... 

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