Preferential absorption

Distribution, Storage and Excretion. Hydrocarbons in each of the aliphatic and aromatic fractions are expected to be distributed throughout tissues and organs following absorption. Preferential distribution to fatty tissues occurs especially with aliphatic hydrocarbons. Ingested or inhaled volatile aliphatic and aromatic hydrocarbons in the HC5-EC8 and EC5-EC9 fractions can be eliminated in exhaled breath as unchanged parent compound. Metabolic elimination of aromatic hydrocarbons in each EC fraction predominately occurs via oxidative metabolic pathways involving... 

Inspection of Eq. (22) reveals that if Kq>1 i.e., if partitioning favors the solvent phase, absorption of solvent lowers the partition coefficient (Kfirst step the diffu-sant partitions in the absence of solvent absorption preferentially toward the solvent phase. In the second step, solvent containing some of the diffusant is absorbed by the polymer. 

Cas-gas Absorption Preferential absorption of one component into a liquid Removal of SO3 from other gases (CSI). Removal of CO2 from synthesis gas (CS2)... 

The most common alternative to distillation for the separation of low-molecular-weight materials is absorption. In absorption, a gas mixture is contacted with a liquid solvent which preferentially dissolves one or more components of the gas. Absorption processes often require an extraneous material to be introduced into the process to act as liquid solvent. If it is possible to use the materials already in the process, this should be done in preference to introducing an extraneous material for reasons already discussed. Liquid flow rate, temperature, and pressure are important variables to be set. 

These chemical effects become important in medicine because living systems operate mostly through the reactions of enzymes, which catalyze all sorts of metabolic reactions but are very sensitive to small changes in their environment. Such sensitivity can lead to preferential absorption of some deleterious isotopes in place of the more normal, beneficial ones. One example in metabolic systems can be found in the incorporation of a radioactive strontium isotope in place of calcium. 

Chemical analysis of the metal can serve various purposes. For the determination of the metal-alloy composition, a variety of techniques has been used. In the past, wet-chemical analysis was often employed, but the significant size of the sample needed was a primary drawback. Nondestmctive, energy-dispersive x-ray fluorescence spectrometry is often used when no high precision is needed. However, this technique only allows a surface analysis, and significant surface phenomena such as preferential enrichments and depletions, which often occur in objects having a burial history, can cause serious errors. For more precise quantitative analyses samples have to be removed from below the surface to be analyzed by means of atomic absorption (82), spectrographic techniques (78,83), etc. 

The primary reference method used for measuring carbon monoxide in the United States is based on nondispersive infrared (NDIR) photometry (1, 2). The principle involved is the preferential absorption of infrared radiation by carbon monoxide. Figure 14-1 is a schematic representation of an NDIR analyzer. The analyzer has a hot filament source of infrared radiation, a chopper, a sample cell, reference cell, and a detector. The reference cell is filled with a non-infrared-absorbing gas, and the sample cell is continuously flushed with ambient air containing an unknown amount of CO. The detector cell is divided into two compartments by a flexible membrane, with each compartment filled with CO. Movement of the membrane causes a change in electrical capacitance in a control circuit whose signal is processed and fed to a recorder. 

Absorption, in which a liquid solvent is used to remove certain compounds from a gas by virtue of their preferential solubility. Examples of absorption involve desulfurization of flue gases using alkaline solutions or ethanolamines,... 

Skin is also important as an occupational exposure route. Lipid-soluble solvents often penetrate the skin, especially as a liquid. Not only solvents, but also many pesticides are, in fact, preferentially absorbed into the body through the skin. The ease of penetration depends on the molecular size of the compound, and the characteristics of the skin, in addition to the lipid solubility and polarity of the compounds. Absorption of chemicals is especially effective in such areas of the skin as the face and scrotum. Even though solid materials do not usually readily penetrate the skin, there are exceptions (e.g., benzo(Lt)pyrene and chlorophenols) to this rule. 

Hydroxylamines ordinarily do not accumulate in the reduction of aromatic nitro compounds for, with some exceptions, most systems in competition will reduce the hydroxylamine function preferentially. Nonetheless, systems have been found that afford the intermediate aromatic hydroxylamine in excellent yield. With hydrogen gas as a reductant and platinum-on-carbon or -on-alumina and about I wt % of DMSO based on nitro compound as a modifier, aromatic hydroxylamines can be formed in 90% yield under mild conditions. The reduction slows markedly after absorption of the second mole of hydrogen and should be stopped at this stage (80). 

Nature of ion exchange resin. The absorption of ions will depend upon the nature of the functional groups in the resin. It will also depend upon the degree of cross-linking as the degree of cross-linking is increased, resins become more selective towards ions of different sizes (the volume of the ion is assumed to include the water of hydration) the ion with the smaller hydrated volume will usually be absorbed preferentially. 

PatU SD, Ngo LY, Glue P, Unadkat JD (1998) Intestinal absorption of ribavirin is preferentially mediated by the Na-l—nucleoside purine (Nl) transporter. Pharm Res 15 950-952... 

The exact site of anthocyanin absorption is not fully known recently it was suggested that the stomach is one of the preferential sites for the process in humans. Interestingly, anthocyanin glycosides are efhciently absorbed in rats (up to 25%) from both stomach " and small intestine, suggesting that anthocyanins have more than one site of absorption along the intestinal tract. 

Studies with rats and chickens given oral doses of TOCP and tn-/ ara-cresyl phosphate provide more definitive evidence that, following absorption, organophosphate esters in hydraulic fluids (or their metabolites) may be widely distributed among tissues with a preferential distribution to fatty tissues, the liver, and the kidneys (Abou-Donia et al. 1990a, 1990b Kurebayashi et al. 1985 Somkuti and Abou-Donia 1990 Suwita and Abou-Donia 1990). 

A study with a dog exposed to an occluded dermal dose of TOCP labeled with radioactive phosphorus provides limited evidence that organophosphate esters in hydraulic fluids may be widely distributed after dermal absorption (Hodge and Sterner 1943). Similar widespread distribution of radioactivity among tissues was observed in male cats after dermal exposure to [uniformly labeled 14C-phenyl]TOCP (Nomeir and Abou-Donia 1986). Tissues and fluids with the highest concentrations of radioactivity in these studies included the bile, gall bladder, urinary bladder, liver, kidney, and fat, thus suggesting that TOCP and metabolites are somewhat preferentially distributed to these tissues. 

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