Chlorinated phenols separation

Figure 4. Separation of twelve different chlorinated phenols by conventional HPLC. The solutes are listed in Table I.

Fig. 4.1 Separation of technical pentachlorophenol using cyclohexane-acetic acid (98 2) as the eluting solvent. Peaks 1, mixture of dioxins and other polychlorinated products 2, mixture of chlorinated phenols including trichlorophenol 3, tetrachlorophenol 4, pentachlorophenol...

Although the GC separation of methyl ethers [16] of phenols has been described, these derivatives are nowadays mainly employed only in special instances, e.g., for increasing the sensitivity of the analysis. The determination of chlorinated phenols in spent bleach liquors from paper mills was reported by Lindstrom and Nordin [17]. A water sample was extracted stepwise with diethyl ether at various pH values, after preliminary purification by means of HPLC, phenols were converted into ethyl ethers by reaction with diazoethane in isooctane—ethanol (9 1) and good reproducibility was achieved. 

Otsuka, K., S. Terabe, and T. Ando, Electrokinetic chromatography with micellar solutions Retention behaviour and separation of chlorinated phenols, J. Chromatogr. 348 39- 47 (1985). 

Chlorinated Phenols HOP and PGP. Two phenolic pollutants derivatized as methyl ethers, pentachlorophenol (PCP) and hexachlorophene (HCP or 2,2 -methylenebls(3,4,6-trlchlorophenol)), eluted with PCB s during TLC separation. The Identities of these compounds In samples were confirmed by comparison of retention times and mass spectra to those of methylated standards. Salient features of these mass spectra are described by Buhler et al. (52). 

Calixarenes are conical-shaped macrocyclic oligomers whose inner cavity can accommodate several guest molecules and, therefore, can serve as a viable option to replace CDs in EKC separations. Environmental examples of the use of calixarene as EKC secondary phases include the separation of chlorinated phenols, benzenediols, and toluidines." Sulfonated calixarenes have also been used as chromophores in the indirect detection of aliphatic amines." ... 

Extraction has to be continued until all lichen substances are dissolved (6-60 h). Often heavily soluble compounds precipitate in the extract and can be removed by filtration. One way to work up the extract is separation in an acid, a phenolic and a neutral part, by shaking successively with a solution of NaHCOj (10% in H2O) and NaOH (2% in HjO). Some compounds, e.g. chlorinated phenolics, are soluble in a solution of Na2C03 (5% in H2O). Shaking should be continued for 10-15 min. Another way is chromatography of the extract over silica gel. The ratio of product to adsorbent is about 1 30 to 1 50, and an approved sequence of eluents is n-hex-ane-diethyl ether-methanol. Many extracts are heavily soluble in n-hexane to overcome this difficulty, the mixture is dissolved in a proper... 

Micellar electrokinetic chromatography (MEKC) has been used by several authors for the separation of phenolic compoimds [103] and in some cases for the determination in water [104], Off-line SPE using pol)nneric sorbents and MEKC with ECD were used for the determination of chlorinated phenols in a river at a low pg/L level [104]. Generally, one problem associated with miniaturized techniques such as CE when combined with UV detection is its limitation to small injection volumes. Therefore, efficient enrichment steps in the sample preparation are necessary. 

Today the sulphonation route is somewhat uneconomic and largely replaced by newer routes. Processes involving chlorination, such as the Raschig process, are used on a large scale commercially. A vapour phase reaction between benzene and hydrocholoric acid is carried out in the presence of catalysts such as an aluminium hydroxide-copper salt complex. Monochlorobenzene is formed and this is hydrolysed to phenol with water in the presence of catalysts at about 450°C, at the same time regenerating the hydrochloric acid. The phenol formed is extracted with benzene, separated from the latter by fractional distillation and purified by vacuum distillation. In recent years developments in this process have reduced the amount of by-product dichlorobenzene formed and also considerably increased the output rates. 

Capillary columns may provide the best method for the separation of phenols prior to their quantification (Eichelberger et al. 1983 Shafer et al. 1981 Sithole et al. 1986). Of the various methods available for detection, the two commonly used methods that are most sensitive are mass spectrometry and flame ionization detection. Although electron capture detectors provide good sensitivities for higher chlorine-substituted phenols, they are poor for phenol itself (Sithole et al. 1986). The best method for the quantification of phenol may be mass spectrometric detection in the selected ion mode, but the loss of qualitative information may be significant (Eichelberger et al. 1983). 

The spectra separate Into two large well separated groups. In the first, smaller clusters can be recognized ortho dlols, para-alkyl phenols, meta-alkyl phenols, ortho-chloro phenols, and multiply chlorinated benzenes. In the second group, these subclusters can be found ortho-alkyl phenols, benzenes bearing chlorine on alkyl side chains, and ortho-chlorotoluenes. 

Tratnyek and Hoigne (1994) investigated 25 substituted phenoxide anions for QSARs that can be used to predict rate constants for the reaction of additional phenolic compounds oxidized by chlorine dioxide (OCIO). Correlating oxidation rates of phenols in aqueous solution is complicated by the dissociation of the phenolic hydroxyl group. The undissociated phenol and the phenoxide anion react as independent species and exhibit very different properties. The correlation analysis should be performed on the two sets of rate constants separately. 

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