Retention of Organic Substances

The end product of protein catabolism, urea, has been studied for almost 200 years and the literature on this subject is vast (B18, F9, Kll, R12). In 1921 Leiter observed that infusing urea into normal dogs produced hypothermia, a frequent 

In renal failure uric acid is also increased, its levels correlating poorly with creatinine (G16). Apparently there is an increase in the extrarenal uric acid elimination by uricolysis in the intestinal tract (B14, S29, S30). This becomes progressively important as plasma uric acid concentration rises (S30). Although hyperuricemia has been implicated in the precipitation of uremic pericarditis (CIO), most investigators believe that uric acid is innocuous, though clearly it may precipitate gout. 

Some investigators suggested that the toxic effects observed during urea infusion experiments were due to products formed from urea (G17) (Fig. 1). Dimhuber and Schultz had shown earlier that cyanate, formed in urea solutions, could cause drowsiness and hyperglycemia (D16, S15). Gilboe and Javid had likewise con- 

Myoinositol and other polyols, such as scylloinositol and neoinositol, are normal constituents of a class of phospholipids known as the phosphoinositides. These compounds, closely related to nervous tissue and neuronal function, are retained in uremia and have been considered a possible cause of peripheral neuropathy (D7, H8, N10). Rats receiving large amounts of myoinositol show a decrease in nerve condition velocity (C12). Adding myoinositol to root ganglion cells in vitro in concentrations known to occur in uremic plasma produces cytotoxic changes (L14). 

In uremic patients an inverse correlation has been observed between nerve conduction velocity and the blood level of myoinositol (Rll). Uremic nerve tissue has been shown to contain increased levels of myoinositol (N6). In hemodialyzed patients, however, there is no correlation between nerve conduction times, the degree of clinical neuropathy or electroencephalographic changes, and the levels of plasma or cerebrospinal fluid myoinositol (B24, Rll). Thus, there is little convincing evidence of an etiological role of myoinositol in the development of neuropathy. 

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Adsorption units are usually not mass produced, they are supplied on the basis of experimental tests for the given technology. For the retention of organic substances, separation efficiencies exceeding 99% may be... 

Kovats, E. 1965. Gas chromatographic characterization of organic substances in the retention index system. Adv. Chromatographia 1 229. 

This method as its name implies is based on the concept of retention indices from gas chromatography. So far the method only has group contribution units worked out for estimating the partitioning of organic substances between polyolefins in contact with ethanol and water but it gives very good estimations for these systems. 

In the optimization of an HPLC method different steps can usually be considered (Fig. 6.1). If only the solvent composition of the mobile phase (i.e. types and amounts of organic modifiers) are considered, one often first optimizes the retention of the substances by selecting a mobile phase with an acceptable solvent strength retention optimization). Retention has to be sufficiently high to achieve separation of the compounds of interest, but also sufficiently low to obtain an acceptable analysis time. Conditions leading to an acceptable retention do not necessarily lead to the separation of all peaks. In a next step the organic modifier composition is adapted (e.g. replacement of one organic modifier by another one) in order to achieve selectivity selectivity optimiza-... 

Recent studies have made it possible to classify water-organic solvent systems in CCC for separation of organic substances on the basis of the liquid-phase density difference, the solvent polarity, and other parameters from the point of view of stationary-phase retention in a CCC column [1,3-9]. Ito [1] classified some liquid systems as hydrophobic (such as heptane-water or chloroform-water), intermediate (chloroform-acetic acid-water and n-butanol-water) and hydrophilic (such as n-butanol-acetic acid-water) according to the hydrophobicity of the nonaqueous phase. Thirteen two-phase solvent systems were evaluated for relative polarity by using Reichardt s dye to measure solvachromatic shifts and using the solubility of index compounds [6]. 

Ion retention is actually ion exchange. Soils give up other ions, H+ or OH- and HCOj, in equal amounts to those retained. When trace ions are removed from the soil solution, the ion exchange to the soil solution is often unnoticed. The retention of organic, nonionic substances usually results in their degradation by soil microbes and conversion to CO2 and water. This chapter is concerned with the exchange, the retention and release, of cations between soil particles and the soil solution. 

Oft, the mobilization of many elements (e.g. U, but not Th, in crystalline rocks) is correlated with the flow of oxidizing water. The mobilization and fixation of uranium involves conqrlexation, redox and retention on minerals via adsorption, and ion exchange. In clay media, the redox potential is strongly bufleied if significant amounts of organic substances ate present. 

Kovats, E. (1965). Gas Chromatographic Characterization of Organic Substances in the Retention Index System. Ado. Chromatogr., Vol.l, pp. 229-247, ISSN 00652415. 

Substances that are solubilized in surfactant micelles can be separated by ultrafiltration through membranes whose pores are smaller in diameter than the micelle size. For a membrane molecular weight cutoff from 1 to 50kDa, the rejections are 98%. The stream of water-containing monomeric molecules of surfactant (permeate) flows through the membrane. The remaining solution (retentate) contains solutes solubilized in micelles. The MEUF process is used for the separation of organic substances and various ions, the latter after their previous complexation. 

Ohi, G., Nishigaki, S., Seki, H., Tamura, Y., Maki, T., Maeda, H., Ochiai, S., Yamada, H., Shimamura, Y., and Yagyu, H., 1975, Interaction of dietary methylmercury and selenium on accumulation and retention of these substances in rat organs, Toxicol. Appl. Pharmacol. 32 527. 

Kovats, E. Gas chromatographic characterization of organic substances in the retention index system. In J. C. Giddings and R. A. Keller, Eds., Advances in Chromatography, p. 229—247. New York Marcel Dekker. 1966. 

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