Ionization, chemical liquid

Atmospheric pressure ionization mass spectrometers, 13 468 Atmospheric pressure chemical ionization (APCI) liquid chromatography, 4 625 Atmospheric Pressure MALDI, 15 658 Atmospheric stability, of organic semiconductors, 22 210... 

Maillard, M.-N., Giampaoli, P., and Cuvelier, M.-E., Atmospheric pressure chemical ionization (APCI) liquid chromatography-mass spectrometry characterization of natural antioxidants, Talanta, 43, 339, 1996. 

GC analysis is performed by using an ion trap mass spectrometer (ITMS) equipped with a chemical liquid ionization system. Figure 6.4 shows the GC-MS chromatogram relative to THPI and captan analysis in a grape sample, analytical conditions are reported in Table 6.13. The... 

Light amplification by stimulated emission of radiation was first demonstrated by Maiman in 1960, the result of a population inversion produced between energy levels of chromium ions in a ruby crystal when irradiated with a xenon flashlamp. Since then population inversions and coherent emission have been generated in literally thousands of substances (neutral and ionized gases, liquids, and solids) using a variety of incoherent excitation techniques (optical pumping, electrical discharges, gas-dynamic flow, electron-beams, chemical reactions, nuclear decay). 

Analytes are introduced into mass spectrometers in gas, liquid, or solid states. In the latter two cases, volatilization must be accomplished either prior to or accompanying ionization. Many ionization techniques are available to produce charged species from analytes the most common ones are electron ionization (electron impact ionization), chemical ionization, matrix-assisted laser desoprtion ionization and atmospheric-pressure ionization (electrospray, atmospheric-pressure chemical ionization, and atmospheric-pressure photoionization). Electron ionization utilizes accelerated electrons (70 eV) colliding with gaseous analyte... 

More quantitative data can be obtained either from reference books or from computerized databanks. Let us deal first with the books. A selection of ionization constants is given in Albert and Serjeant (1984). Exhaustive compilations of ionization constants are listed on p. 383. Recently determined values may be located through Chemical Abstracts through the entry Ionization in Liquids in the General Subject Index, or under the name of the particular substance in the Chemical Substance Index. For the prediction of ionization constants from the chemical structure, see Perrin, Dempsey and Serjeant (1981). The standard compilations of the stability constants of chelated metals are given at the end of Section 11.3 (p. 459). 

Photo-ionization in liquids and crystals and the dependence of the frequency of X-ray absorption edges on chemical constitution. Phys. Rev. 34 (1929) 954-963. 

The ionization of an ionic salt, such as NaCl (see Equation 11.10), poses a special problem. The un-ionized chemical species in this equilibrium is not dissolved. This is an example of what is termed a heterogeneous equilibrium (i.e., two or more of the equilibrium participants are present in different phases [solid, liquid, gas, or dissolved]). In this case, we have a solid that is not dissolved while everything else is dissolved. Since the solid is undissolved, it does not make sense to refer to its molar concentration. An interesting and important fact about this undissolved solid is that regardless of how much is present, the concentrations of the dissolved ions are constants (at a given temperature). Thus, while the molar concentrations of the ions are real numbers, the molar concentration of the un-ionized species is a nonsensical term. In this case, a special equilibrium constant is defined which uses only the molar concentrations of the dissolved ions in its definition. This special equilibrium constant is called the solubility product constant (K p), which is defined as the mathematical product of the molar concentrations of the ions raised to the power of their balancing... 

With the ion traps that offer the possibility of performing negative chemical ionization with liquid reactants, methanol is a preferred reactant in negative mode. The reagent ions are then methanolate ions CHjO formed according to reactions 6 and 7 in Figure 9.63. 

The term nebulizer is used generally as a description for any spraying device, such as the hair spray mentioned above. It is normally applied to any means of forming an aerosol spray in which a volume of liquid is broken into a mist of vapor and small droplets and possibly even solid matter. There is a variety of nebulizer designs for transporting a solution of analyte in droplet form to a plasma torch in ICP/MS and to the inlet/ionization sources used in electrospray and mass spectrometry (ES/MS) and atmospheric-pressure chemical ionization and mass spectrometry (APCI/MS). 

Liquids that are sufficiently volatile to be treated as gases (as in GC) are usually not very polar and have little or no hydrogen bonding between molecules. As molecular mass increases and as polar and hydrogen-bonding forces increase, it becomes increasingly difficult to treat a sample as a liquid with inlet systems such as El and chemical ionization (Cl), which require the sample to be in vapor form. Therefore, there is a transition from volatile to nonvolatile liquids, and different inlet systems may be needed. At this point, LC begins to become important for sample preparation and connection to a mass spectrometer. 

Direct liquid introduction interface. An interface that continuously passes all, or a part of, the effluent from a liquid chromatograph to the mass spectrometer the solvent usually functions as a chemical ionization agent for ionization of the solute. 

Perfluorinated carboxylic acids are corrosive liquids or solids. The acids are completely ionized in water. The acids are of commercial significance because of their unusual acid strength, chemical stabiUty, high surface activity, and salt solubiUty characteristics. The perfluoroaLkyl acids with six carbons or less are hquids the higher analogues are soHds (Table 1). 

A liquid chromatography-mass spectrometry (LC-MS) method that can quantitatively analyze urinar y normal and modified nucleosides in less than 30 min with a good resolution and sufficient sensitivity has been developed. Nineteen kinds of normal and modified nucleosides were determined in urine samples from 10 healthy persons and 18 breast cancer patients. Compounds were separ ated on a reverse phase Kromasil C18 column (2.1 mm I.D.) by isocratic elution mode using 20 mg/1 ammonium acetate - acetonitrile (97 3 % v/v) at 200 p.l/min. A higher sensitivity was obtained in positive atmospheric pressure chemical ionization mode APCI(-i-). 

I. Fener, V. Pichon, M-C. Hennion and D. Barcelo, Automated sample preparation with exti action columns by means of anti-isoproturon immunosorbents foi the determination of phenylurea herbicides in water followed by liquid chi omatography-diode aixay detection and liquid cliromatogi aphy-atmospheric pressure chemical ionization mass spectrometiy , 7. Chromatogr. 777 91-98 (1997). 

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