Surface-mediated ionization

Offline-surface mediated approach Collect effluent from multiple LCs on surface place surface in MS interface use fast, surface-mediated ionization methods such as MALDI, DESI, etc. to sample effluents... 

As the droplets move through the hot source area, they continue to vaporize. The electric field at the liquid surface increases until ions present in the eluent are ejected from the droplet. Ions are sampled through a conical exit aperture in the mass analyzer. The ionization of the analytes takes place by means of direct ion evaporization of the sample ion or by solvent-mediated CI reactions an ion of the electrolyte ejected from a droplet reacts with a sample molecule in the gas phase and generates a sample ion that is mass analyzed. In addition, fragment ions can be observed due to the high temperatures associated with TSP negative ions are also produced by TSP, and negative ion detection is recommended for acidic compounds. 

When one considers the role of the matrix in the particle-induced emission of secondary ions it is no wonder that it is so difficult to unravel all the processes that take place. The matrix is the medium in which the primary excitation occurs. It must also disperse some of that energy to sites at the surface where secondary ion emission occurs. It must provide the species to be desorbed and at the same time mediate the ionization process. In an attempt to understand these complex coupled processes we have tried to simplify the system by first selecting a homogeneous substrate for the energy deposition and then studying the ionization-emission process for species that are present as a submonolayer on the surface (26). 

Albanese J., Dainiak N., Modulation of intercellular communication mediated at the cell surface and on extracellular, plasma membrane-derived vesicles by ionizing radiation. Experimental Hematology, 2003,31,455-464. 

Beyond neat liquid water sum-frequency vibrational spectroscopy allowed the study of the alkyl chain conformation of surfactants such as dodecyl sulfate described in Ch. 9, that mediates the interfaces between water and CCI4 when the head group or the cations of these amphiphile molecules varied (77, 78). It also gave experimental evidence that the water surface favours the presence of anions rather than cations (79). This effect is at the origin of the oxidative power of sea water, which is ascribed to Cl anions positioned on surfaces of liquid-water droplets. It has also been applied to other H-bonded liquid water, such as methanol, where it could be demonstrated that the CH3 groups point away from the liquid at the interface with vapour (73). This is also the case for CH3 groups of acetic acid (80). Also the surface of liquid water could be shown (81) to be disrupted by even such a small amount as 0.3% of acetic acid, which does not ionize, even at this low... 

MALDl is a surface ionization technique that is based on energy transfer from the absorbed laser light to the sample leading to simultaneous desorption and ionization. Energy transfer is mediated by a so-called matrix, which absorbs in the wavelength region of laser emission. Figure 4 illustrates several compounds... 

Surface-assisted laser desorption/ionization is a laser-induced ionization method developed in parallel to the more well-known matrix-assisted laser desorption/ionization (MALDI) method. Using inorganic materials as energy-mediating media, it has been exploited as a possible alternative to MALDI, especially in small molecule detection (1—4). The most successful SALDI substrate was reported by Siuzdak and coworkers, in which a silicon surface of mesoporous features was used, commonly termed as... 

Structural Physicochemical Biochemical Pharmacokinetic Molecular weight, ionization, polarity, lipophilicity/hydrophilicity, shape, reactivity, polar surface area, H-bonding Solubility, dissolution rate, permeability, chemical stability Protein/tissue/cell binding, metabolism, receptor mediated transport (influx and efflux) Bioavailability, half-life, clearance, drug-drug interactions, toxicity, maximum concentrations in plasma... 

In summary, the initial formation of an allylic radical anion on the metal surface is the most likely event, which would explain the success of indium, as its first ionization potential is particularly low E - 5.79 eV). In tin- and indium-mediated reactions the second step should be the insertion of the metal cation into the carbon-bromine (chlorine) bond to afford organometallic intermediates, which are stable enough to be produced, but also highly reactive toward carbonyl compounds in aqueous media. 

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