Ethyl cyclohexane, adsorption

We then designed model studies by adsorbing cinchonidine from CCU solution onto a polycrystalline platinum disk, and then rinsing the platinum surface with a solvent. The fate of the adsorbed cinchonidine was monitored by reflection-absorption infrared spectroscopy (RAIRS) that probes the adsorbed cinchonidine on the surface. By trying 54 different solvents, we are able to identify two broad trends (Figure 17) [66]. For the first trend, the cinchonidine initially adsorbed at the CCR-Pt interface is not easily removed by the second solvent such as cyclohexane, n-pentane, n-hexane, carbon tetrachloride, carbon disulfide, toluene, benzene, ethyl ether, chlorobenzene, and formamide. For the second trend, the initially established adsorption-desorption equilibrium at the CCR-Pt interface is obviously perturbed by flushing the system with another solvent such as dichloromethane, ethyl acetate, methanol, ethanol, and acetic acid. These trends can already explain the above-mentioned observations made by catalysis researchers, in the sense that the perturbation of initially established adsorption-desorption equilibrium is related to the nature of the solvent. 

In analyses of extract from freeze-dried fish [89] gel chromatography on Bio-Beads S-X3 with cyclohexane/ethyl acetate (1/1) was used for removal of neutral fat. Then adsorption column chromatography on silica gel (1.5% water) according to the multi-residue procedure of Specht and Tillkes [93] was applied. Elution with n-hexane separated TCBTs and PCBs from the main portion of organochlorine pesticides and other more polar compounds. The hexane extract was evaporated to 0.5 ml for GC-MS determination [89,90]. 

Reiger and Ballschmiter [43] described a multistep method for PCA analysis in sewage sludge by cyclohexane-isopropanol extraction and cleanup on silica gel column chromatography. Fractionation on silica gel was achieved by eluting with hexane (FI), which desorbed hexachlorobenzene, 4,4 -DDE, PCB, PCDD, and PCDF. PCAs were then desorbed from the column with (90 10) hexane/di-ethyl ether. The recovery of PCAs by this method was 86%. These authors also noted that cleanup chromatography on activated alumina should be avoided because PCAs were either totally or partially destroyed by dehydrochlorination during the adsorption process. 

The mobile phase competes with the sample components for adsorption sites on the stationary phase and thereby decreases the number of adsorption sites which are available for the solutes (i.e. sample components). Consequently, use of increasingly polar mobile phases decreases the retention times of solutes. Several solvents used in LSC in order of increasing polarity are Fluoroalkanes, petroleum ether, carbon tetrachloride, cyclohexane, toluene, benzene, esters, chloroform, ethyl ether, dichloroethane, methyl ethyl ketone, acetonitrile, alcohols, water, pyridine, organic acids. 

For the separation of decaborane on silica, Hermanek (42) has noted that tetrahydrofurane and ethyl ether appear anomalously weak as solvents. The apparent eluotropic series is tetrahydrofurane, n-hexane i% cyclohexane, ethyl ether, CCI4 (cf. Table 8-1), followed by several stronger solvents in approximately their normal order. The greater adsorption of decaborane from the two ether solvents is attributed to the formation of a polar decaborane-ether adduct, which is expected to be more strongly adsorbed than the nonpolar decaborane. 

The classical thermodynamic approach has been applied to liquid phase adsorption by Larionov and Myers and by Minka and Myers. It was shown that for sorption of carbon tetrachloride-isooctane and benzene-carbon tetrachloride on aerosil the adsorbed solutions show approximately ideal behavior whereas adsorbed mixtures of benzene, ethyl acetate, and cyclohexane on activated carbon showed appreciable deviations from ideality. However, it is shown that the activity coefficients and hence the adsorption equilibrium data for the ternary systems may be successfully predicted, by classical methods, from data for the constituent binaries. 

Poly(methyl methacrylate) and polytetrahydrofuran polymers were studied at the critical point of adsorption. This critical point of adsorption occurs where the retention of a given polymer is governed strictly hy the number and types of functional groups on the polymer [858]. The authors show plots of log MW vs. retention time for various mobile phase compositions on a given column. The critical point is reached when the retention time becomes independent of the molecular weight of the polymer. For poly(methyl methacrylate) that point was reached on a silica column (RI detector) with a 73/27 methyl ethyl ketone/cyclohexane mobile phase. For polytetrahydrofuran, the silica column and a 95/5 acetone/hexane mobile phase created the critical conditions. This approach has enabled the individual blocks within the co-polymer to be studied (i.e., the portion of the polymer that can make contact with the support surface). 

Alumina Silicic acid Magnesium sulfate Cellulose paper 1 Increasing adsorption of polar materials Water t Methanol Ethanol Acetone Ethyl acetate Diethyl ether Methylene chloride Cyclohexane Pentane 1 Increasing solvation of polar materials... 

Figure 14.8 Modelling of the adsorption isotherms (surface excess) of liquid solutions on activated carbon using MPTA. (a) Ethyl acetate + cyclohexane atT = 303.15 K (b) ethanol + cyclohexane atT = 303.15 K. Reprinted from Monsalvo and Shapiro (2007b), with permission from Elsevier...

Helmroth and co-workers [2] in the course of studying the effect of solvent adsorption on additive migration from low-density polyethylene described a gas chromatographic (GC) method for the determination of this antioxidant in the solvents used in the extraction studies. These include cyclohexane, ethanol, ethyl acetate, isooctane, isopropanol, olive oil, tributyrin and tricaprylin. 

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