Neutral species

Ion chemistry experiments can also provide information about the thermochemistry of neutral molecules50. Guided ion-beam mass spectrometry experiments45 allow us to 

Given the sublimation enthalpy6 of Ag as 284.6 kJ mol-1, we conclude that reaction 23 

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The same procedure as outlined above can be used to study ion-molecule reactions [15, 34]- Mass-selected ions will react with neutral species inside the trap. The presence of the damping gas means that stable (tliemiodynamic and... 

PHOTOLYSIS OF AMMONIA. Restricting the discussion to neutral species only (ionic ones require high energy, and are not important in the 170-220-nm UV range, where ammonia absorbs strongly), the two low-energy reaction channels to ground state products are... 

A substance exists as a liquid rather than a gas because attractive forces between molecules (mtermolecular attractive forces) are greater m the liquid than m the gas phase Attractive forces between neutral species (atoms or molecules but not ions) are referred to as van der Waals forces and may be of three types... 

Free radical (Section 4 16) Neutral species in which one of the electrons in the valence shell of carbon is unpaired An ex ample is methyl radical CH3... 

Capillary zone electrophoresis also can be accomplished without an electroosmotic flow by coating the capillary s walls with a nonionic reagent. In the absence of electroosmotic flow only cations migrate from the anode to the cathode. Anions elute into the source reservoir while neutral species remain stationary. 

Capillary zone electrophoresis provides effective separations of any charged species, including inorganic anions and cations, organic acids and amines, and large biomolecules such as proteins. For example, CZE has been used to separate a mixture of 36 inorganic and organic ions in less than 3 minutes.Neutral species, of course, cannot be separated. 

Micellar Electrokinetic Capillary Chromatography One limitation to CZE is its inability to separate neutral species. Micellar electrokinetic chromatography... 

Because micelles are negatively charged, they migrate toward the cathode with a velocity less than the electroosmotic flow velocity. Neutral species partition themselves between the micelles and the buffer solution in much the same manner as they do in HPLC. Because there is a partitioning between two phases, the term chromatography is used. Note that in MEKC both phases are mobile. ... 

The elution order for neutral species in MEKC depends on the extent to which they partition into the micelles. Hydrophilic neutrals are insoluble in the micelle s hydrophobic inner environment and elute as a single band as they would in CZE. Neutral solutes that are extremely hydrophobic are completely soluble in the micelle, eluting with the micelles as a single band. Those neutral species that exist in a partition equilibrium between the buffer solution and the micelles elute between the completely hydrophilic and completely hydrophobic neutrals. Those neutral species favoring the buffer solution elute before those favoring the micelles. Micellar electrokinetic chromatography has been used to separate a wide variety of samples, including mixtures of pharmaceutical compounds, vitamins, and explosives. 

Capillary Electrochromatography Another approach to separating neutral species is capillary electrochromatography (CEC). In this technique the capillary tubing is packed with 1.5-3-pm silica particles coated with a bonded, nonpolar stationary phase. Neutral species separate based on their ability to partition between the stationary phase and the buffer solution (which, due to electroosmotic flow, is the mobile phase). Separations are similar to the analogous HPLC separation, but without the need for high-pressure pumps, furthermore, efficiency in CEC is better than in HPLC, with shorter analysis times. 

Methanol, which elutes at 4.69 min, is included as a neutral species to indicate the electroosmotic flow. When using standard solutions of each vitamin, CZE peaks are found at 3.41 min, 4.69 min, 6.31 min, and 8.31 min. Examine the structures and p/Ca information in Figure 12.47, and determine the order in which the four B vitamins elute. 

Vitamin Bi is a cation and must, therefore, elute before the neutral species methanol thus it elutes first at 3.41 min. Vitamin B3 is a neutral species and should elute with methanol at 4.69 min. The remaining two B vitamins are weak acids that partially ionize in the pH 9 buffer. Of the two, vitamin Be is the stronger acid and is ionized (as the anion) to a greater extent. Vitamin Be, therefore, is the last of the vitamins to elute. 

Ions impacting onto the cathode during a discharge cause secondary electrons and other charged and neutral species from the electrode material to be ejected. Some of these other particles derived... 

Similarly, the rate of evaporation of neutral species from a filament surface is given by Equation 7.4, in which Cq is the surface density of atoms on the surface (a complete monolayer of atoms would have a surface density of about 10 atoms/cm ). 

The Z-spray inlet/ionization source sends the ions on a different trajectory that resembles a flattened Z-shape (Figure 10.1b), hence the name Z-spray. The shape of the trajectory is controlled by the presence of a final skimmer set off to one side of the spray instead of being in-line. This configuration facilitates the transport of neutral species to the vacuum pumps, thus greatly reducing the buildup of deposits and blockages. 

The mass of an electron is very small, and, for most practical purposes, the mass of an ion is the same as that of the corresponding neutral species, viz., M = M = M. ... 

If the applied electromagnetic field is an alternating one, then the electrons and ions are pushed (or pulled) backward and forward as the sign of the field changes. At high frequencies of applied fields, this motion causes multiple collisions between ions and neutral species and between electrons and ions and neutral species. 

Additional ionization occurs by collision between the ions and other neutral species (ion/molecule collision see Chapter 1). Unless special steps are taken (see Chapters 8 and 11 ), the ions formed do not fragment, so little or no structural information is obtained. However, the lack of fragmentation does mean that good relative molecular mass data can be obtained. The assembly of ions formed by ion... 

Plasma consists of a gaseous mixture of neutral species, ions, and electrons. The charged species are in approximately equal concentrations. 

Mass analysis. A process by which a mixture of ionic (or neutral) species is separated according to the mass-to-charge (m/z) ratios (for ions) or their aggregate atomic masses (for neutrals). The analysis can be qualitative or quantitative. 

Thermal desorption. The vaporization of ionic or neutral species from the condensed state by the input of thermal energy. The energy input mechanism must be specified. 

Charge-exchange (charge transfer) ionization. Occurs when an ion/atom or ion/molecule reaction takes place in which the chaise on the ion is transferred to the neutral species without any dissociation of either. 

Ionic dissociation. Decomposition of an ion into another ion of lower formula weight, plus one or more neutral species. 

Metastable ion. An ion that is sufficiently excited to dissociate into a particular daughter ion and neutral species during the flight from the ion source to the detector. The dissociation is most readily observed when it takes place in one of the field-free regions in a mass spectrometer. 

Parent ion. An electrically charged molecular moiety that may dissociate to form fragments, of which one or more may be electrically charged, and one or more are neutral species. A parent ion can be a molecular ion or an electrically charged fragment of a molecular ion. 

Association reaction (associative combination). The reaction of a (slow moving) ion with a neutral species, wherein the reactants combine to form a single ionized species. 

Chaise-transfer reaction. An ion/neutral reaction wherein the charge on the reactant ion is transferred to the reactant neutral species so that the reactant ion becomes a neutral entity. 

Collision-induced dissociation (or decomposition), abbreviated CID. An ion/neutral process wherein the (fast) projectile ion is dissociated as a result of interaction with a target neutral species. This is brought about by conversion during the collision of part of the translational energy of the ion to internal energy in the ion. The term collisional-activated dissociation (or decomposition), abbreviated CAD, is also used. 

Ionizing collision. An ion/neutral reaction in which an electron or electrons are stripped from the ion and/or the neutral species in the collision. Generally, this term describes collisions of fast-moving ions or atoms with a neutral species in which the neutral species is ionized. Care should be taken to emphasize if charge stripping of the ion has taken place. 

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