Ionization, chemical external

Ion traps with hybrid sources are not presented in the table. As long as they allow working alternatively in internal ionization and external ionization, they combine the advantages and possibilities of both systems. Rare artifacts can nevertheless complicate the interpretation of mass spectra in hybrid mode. Ghost ions can indeed appear in the chemical ionization mass spectra of certain compounds. ... 

Internal and External Phases. When dyeing hydrated fibers, for example, hydrophUic fibers in aqueous dyebaths, two distinct solvent phases exist, the external and the internal. The external solvent phase consists of the mobile molecules that are in the external dyebath so far away from the fiber that they are not influenced by it. The internal phase comprises the water that is within the fiber infrastmcture in a bound or static state and is an integral part of the internal stmcture in terms of defining the physical chemistry and thermodynamics of the system. Thus dye molecules have different chemical potentials when in the internal solvent phase than when in the external phase. Further, the effects of hydrogen ions (H" ) or hydroxyl ions (OH ) have a different impact. In the external phase acids or bases are completely dissociated and give an external or dyebath pH. In the internal phase these ions can interact with the fiber polymer chain and cause ionization of functional groups. This results in the pH of the internal phase being different from the external phase and the theoretical concept of internal pH (6). 

Where the feed contains a large proportion of treated water, softening is a minimum requirement and the raw water quality dictates whether a more sophisticated form of external treatment would be preferable. If the water has a high alkalinity it calls for de-alkalization and base exchange. De-ionization is the ideal water treatment, but is usually avoided if possible because of its cost and use of corrosive chemicals. Membrane processes giving partial de-ionization are not normally installed at present, but are certain to become important in the future. 

Wu, H.-F. Lin, Y.-P. Determination of the Sensitivity of an External Source Ion Trap Tandem Mass Spectrometer Using Dimethyl Ether Chemical Ionization. J. Mass Spectrom. 1999,54,1283-1285. 

Pulsed-Valve Cl and CID-Exneriments. Chemical Ionization (Cl), self-CI (SCI), and direct or desorption Cl (DCI) experiments in FTMS can be done equally well with the differentially-pumped external ion source described below, or with a pulsed-valve single cell arrangement (5,6). In our experiments, we admit a pulse of reagent gas via a piezoelectric pulsed valve with a minimum opening time of about 2.5 ms (7). Unlike solenoid pulsed valves, the performance of piezoelectric pulsed valves is not disturbed by the strong magnetic field of 4.7 Tesla. 

A most important aspect of the tunneling mechanism as applied to low-temperature irradiation-induced chain conversions in a solid is the assumption of energy equilibrium in a reacting solid-state system. However, the universality of kinetic models of the above processes based on the Arrhenius equilibrium law has neven been considered an axiom—especially in studies of chemical reactions stimulated externally by ionizing radiation, that is, under conditions where temperature was no longer the only parameter characterizing the energy state of the system. 

A structure-function study of a proton pathway in the y-class carbonic anhydrase from Methanosarcina thermophila was conducted in the work of Tripp and Ferry (2000). Four enzyme glutamate residues were characterized by site-directed mutagenesis. It was shown that Glu 84 and an active site residue, Glu 89, are important for CO2 hydration activity, while external loop residues, Glu 88 and Glu 89 are less important. Glu 84 can be substituted for other ionizable residues with similar pKa values and, therefore, participates in the enzyme catalysis not as a chemical reagent but as a proton shuttle. 

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