Chromatography, on carbon

It is difficult to conclude what the best analytical method is for PCDEs but, based on the literature, microcolumns such as Florisil [57] seem to be effective in separation of PCDEs from PCDDs and PCDFs. Furthermore they are fast and inexpensive. Before PCDEs can be analyzed by MS, however, an additional cleanup step is needed. This has been performed using column chromatography on carbon, since silica gel and neutral alumina microcolumns have not worked well with fish extracts for this purpose [57]. Activated silica and alumina microcolumns, however, could possibly be alternatives for a carbon column. An activated silica column has been used an additional cleanup step after Florisil and carbon column chromatography in the case of mussel extracts [123]. It is not necessary to separate PCBs from PCDEs, since PCBs have been reported not to interfere in the MS analysis of PCDEs [57,130],... 

Fio. 5.—Chromatography on Carbon (Carboraffin Supra) of a Mixture of n-Glu-cose, Sucrose, and Raffinose by Displacement Development with 0.5% Ephedrine in Water (Refractive Index vs. Volume of Developer). ... 

The solvent-strength parameters for the common solvents used in normal phase chromatography on carbon are quite different from those of silica or alumina. Thus carbon offers quite different selectivities than alumina and silica for normal-phase chromatography. However, the lack of a reproducible commercial source for carbon was for many years a significant limitation to its widespread application. In addition the sensitivity of carbon to changes in solvent strength is much less than that of silica or alumina. 

Although the principal oligosaccharide of milk is lactose, this disacchaiide is accompanied by smaller amounts of other oligosaccharides, which can be separated from lactose by adsorption on activated carbon and elution with dilute acetic acid. The amounts vary somewhat with the mammalian species. In human milk, the concentration, exclusive of lactose, is about 3 g per liter. Preparative chromatography on carbon-Celite and cellulose columns has led to the isolation of live oligosaccharides in pure form (see Table X). 

The irradiation of tetra-/-butylcyclopentadienone with 254 nm light at 77 K produced a tricyclopentanone which, upon extended irradiation, lost carbon monoxide. Tetra-f-butyltetrahedrane was formed. This derivative of the second fundamental hydrocarbon of molecular formula (CH), namely tetrahedrane, is stable at room temperature and could be isolated after chromatography on silica gel in crystalline form (G. Maier, 1978). 

Diaziridines also show slow nitrogen inversion, and carbon-substituted compounds can be resolved into enantiomers, which typically racemize slowly at room temperature (when Af-substituted with alkyl and/or hydrogen). For example, l-methyl-3-benzyl-3-methyl-diaziridine in tetrachloroethylene showed a half-life at 70 °C of 431 min (69AG(E)212). Preparative resolution has been done both by classical methods, using chiral partners in salts (77DOK(232)108l), and by chromatography on triacetyl cellulose (Section 5.08.2.3.1). 

For selective estimation of phenols pollution of environment such chromatographic methods as gas chromatography with flame-ionization detector (ISO method 8165) and high performance liquid chromatography with UV-detector (EPA method 625) is recommended. For determination of phenol, cresols, chlorophenols in environmental samples application of HPLC with amperometric detector is perspective. Phenols and chlorophenols can be easy oxidized and determined with high sensitivity on carbon-glass electrode. 

The purity of cyclobutanone was checked by gas chromatography on a 3.6-m. column containing 20% silicone SE 30 on chromosorb W at 65°. The infrared spectrum (neat) shows carbonyl absorption at 1779 cm. - the proton magnetic resonance spectrum (carbon tetrachloride) shows a multiplet at 8 2.00 and a triplet at S 3.05 in the ratio 1 2. 

Sufficient data are not yet available to allow evaluation of the relative merits of palladium-on-carbon and degassed Raney nickel catalysts. Comparable yields of 2,2 -biquinolines have been obtained by both methods under suitable conditions but the percentage conversions with degassed Raney nickel have been found to be much lower, reflecting the extent of side reactions with this catalyst. However, work in this laboratory has shown that the reaction of quinoline with palladium-on-carbon is not free from complications for example, at least three products in addition to 2,2 -biquinoline have been detected by paper chromatography. 

Fig. 8. Preparative isolation of hexon antigen of EDS-76 by hydrophobic-interaction chromatography on Butyl-PG column (2x5 cm) (A) application of the allantoic fluid diluted (1 5) by 50 mM potassium acetate, pH 4,130 ml (B)0.01 mol/1 potassium acetate, pH 5.5 (C) 0.01 mol/1 potassium bicarbonate pH 8.0, 10% isopropanol (D) 0.01 mol/1 potassium carbonate pH 9.6, 10% isopropanol. EDS-0 — components of alantoic fluid eluted with buffer A, EDS-1 — desorbed hexon fraction eluted with buffer C, EDS-2 — fraction desorbed with buffer D [56]...

A mixture of TMSOTf (0.1 mmol, lmol%), allyltrimethylsilane (11.5 mmol) and dichioromethane (1 ml) was cooled to -78 °C, and to this was added benzaldehyde dimethylacetal (10.5 mmol) in dichioromethane (4ml). The resulting mixture was stirred for 6h at —78°C, and then poured into saturated sodium hydrogen carbonate solution (10 ml) and extracted with ether (3 x 20 ml). The combined organic extracts were washed with brine, dried and concentrated. Chromatography on silica gel (1 20 ether hexane) gave 4-pheny]-4-methoxybut-l-ene (9.2mmol, 88%). 

An aqueous solution of HF (40%, 2eq.) was added to a solution of the substrate in MeCN at either 0°C or at ambient temperature. When the reaction was complete by t.l.c. analysis (ca. 30min), excess sodium hydrogen carbonate solution (8%) was added, and the product was extracted with ether. The product was purified by flash chromatography on silica gel. 

A solution of Pd(OAc)2 (0.05 mmol) and bis(diphenylphosphino)ethane (0.05 mmol) in acetonitrile (1 ml) was heated gently to reflux, at which time a solution of the silyl enol ether (1 mmol) and diallyl carbonate (2 mmol) in MeCN (4 ml) was added in one portion. The mixture was heated under reflux for 1-3 h, the course of reaction being monitored by t.l.c. or g.l.c. analysis. On completion, the cooled reaction solution was filtered through fluorosil. The pure a/ -unsaturated compound was isolated by column chromatography on silica gel (70-95%). 

A solution of 2-methyl-l-(trimethylsilyloxy)cyclohex-l-ene (10 mmol) in dichloromethane (8 ml) was added dropwise over 15 min with stirring to acetyl chloride (10 mmol) and TiCl4 (10 mmol) in dichloromethane (15 ml) at -78 °C. After 1 h at -78 °C, the reaction mixture was allowed to warm to ambient temperature over 2h. It was then diluted with ether (20ml), and poured into saturated sodium hydrogen carbonate solution (50 ml). Normal work-up, followed by chromatography on silica gel, gave the /1-diketone (9.1 mmol, 91%). 

A solution of 1-trimethylsilyloxycyclohex-l-ene (5.12 mmol) and benzaldehyde dimethyl acetal (5.47 mmol) in dichloromethane (15 ml) was cooled to —78°C, and to this was added TMSOTf (0.05 mmol) in dichloromethane (0.5 ml). The mixture was stirred at -78°C for 8h, and then quenched by the addition of water at —78 °C. Dichloromethane (50 ml) was added, and the mixture was washed with saturated sodium hydrogen carbonate solution and brine, and dried. Concentration provided a crude oil consisting of a 93 7 mixture of erythro- and r/jreo-2-(methoxyphenyl-methyl)cyclohexanone. Chromatography on silica gel (20g, eluant petroleum ether ether 10 1) gave the pure erythro (82%) and threo (6.7%) isomers as oils. 

The partially hydrolysed material was fractionated by size exclusion chromatography on a Bio Gel PIO (Bio Rad) column (2,6 x 90 cm) and eluted with 50 mM ammonium hydrogen carbonate at 20 ml/h and fractions of 3.2 ml each were collected. Fractions 45-70 were pooled and subjected to HPAEC-PAD for further separation. 

Jackson, P. T., Schure, M. R., Weber, T. P., and Carr, P.W., Intermolecular interactions involved in solute retention on carbon media in reversed-phase high-performance liquid chromatography, Anal. Chem., 69(3), 416, 1997. 

Yamaki, S., Isobe, T., Okuyama, T., Shinoda, T., Reversed-phase liquid chromatography on a microspherical carbon column at high temperature, /. Chromatogr. A, 728(1 2), 189, 1996. 

Storr-Hansen, E. and T. Cederberg. 1992. Determination of coplanar polychlorinated biphenyl (CB) congeners in seal tissues by chromatography on active carbon, dual-column high resolution GC/ECD and high resolution GC/high resolution MS. Chemosphere 24 1181-1196. 

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