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Query: EC:3.4.15.1 (ACE)
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Toxic organic compounds detected generally in source water could combine with chlorine and contribute significantly to chlorination disinfection by-products (CDBPs). The effects of pH on species distribution of CDBPs and the kinetics of chlorination were investigated using phenol as a model of ionizable toxic organic compounds in the pH range of 6.0-9.0. It was found that five chlorination products including 2-monochlorophenol (2-MCP), 4-monochlorophenol (4-MCP), 2,6-dichlorophenol (2,6-DCP), 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (TCP) were produced by successive chlorination substitution. MCP (2-MCP and 4-MCP) were the dominant products and phenol partly remained in acid media, while TCP and DCP (2,6-DCP and 2,4-DCP) were the main components in neutral and alkaline media. A steady equilibrium of phenol and its chlorination products was reached in 20-30 min in acid-, neutral- and slightly alkaline media, and was delayed to 60-180 min in alkaline media. The difference in properties between phenols and phenolates, and those between HOCl and ClO(-) should be considered simultaneously in explaining the effects of pH on the chlorination process with the theory of electrophilic substitution. These results show that pH plays an important regulating role in the species distribution of CDBPs and the kinetics of chlorination for ionizable toxic organic compounds in chlorination.
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PMID:Effects of pH on the chlorination process of phenols in drinking water. 1633 40

Phenol, 2,4-dichlorophenol (2,4-DCP), and 2,4,6-trichlorophenol (2,4,6-TCP) were baseline separated by using a homemade microchip CE with an end-channel amperometric detector where a 50 microm Pt microdisk working electrode (WE) and a Pt cathode were integrated onto the microchip itself. Separation parameters such as injection time and voltage, pH of the buffer, online pretreatment condition for WE, reproducibility, and detection potential were investigated. Under the selected separation conditions, the linear ranges for phenol, 2,4-DCP, and 2,4,6-TCP were 2-200, 4-400, and 4-400 microM, respectively. The LODs were 0.4, 0.5, and 0.7 microM for phenol, 2,4-DCP, and 2,4,6-TCP, respectively (S/N = 3). The standard addition method was successfully applied to the analysis of landfill leachate samples and the concentration of phenol in the landfill leachate samples was measured to be 0.32 and 0.21 mM, respectively. The recoveries were in the range of 85-103% and corresponding RSDs were less than 5.5%.
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PMID:Determination of phenol in landfill leachate by using microchip capillary electrophoresis with end-channel amperometric detection. 1648 19

The 1-octyl-3-methylimidazolium hexafluorophosphate ([C8MIM][PF6]) ionic liquid was immobilized in the pores of a polypropylene hollow fiber for hollow fiber-protected liquid-phase microextraction. Analytes including 4-chlorophenol (4-CP), 3-chorophenol (3-CP), 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP) were extracted into this ionic liquid membrane, and back extracted into 10microL sodium hydroxide acceptor solution in the lumen of the hollow fiber. Then, the acceptor solution was withdrawn into the high-performance liquid chromatography (HPLC) microsyringe connected to the hollow fiber, and directly injected into the HPLC system for analysis. Some parameters that might affect the extraction efficiency were optimized, and low detection limits (0.5microgL(-1) for 4-CP, 3-CP, DCP and 1.0microgL(-1) for TCP) were obtained. Good repeatability was achieved because of the stability of the hollow fiber-supported ionic liquid membrane. The proposed procedure was applied for direct determination of the four chlorophenols in some real water samples including groundwater, river water, wastewater and tap water. All of the four chlorophenols in these water samples were under the limits of determination, and the recoveries were in the range of 70.0-95.7% at 5microgL(-1) spiked level.
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PMID:Direct determination of chlorophenols in environmental water samples by hollow fiber supported ionic liquid membrane extraction coupled with high-performance liquid chromatography. 1711 89

The catalytic dechlorination of five chlorophenols, by Ni/Fe bimetal was investigated through batch experiments. The results showed that the destruction of chlorophenols by hydrodechlorination over Ni / Fe was very effective and followed the pseudo-first-order kinetics under aqueous conditions. The order of reaction rate was 2-chlorophenol > 4-chlorophenol > 2,4-dichlorophenol > 2,4,6-trichlorophenol > 2,6-dichlorophenol (2,6-DCP). The dechlorination rate of chlorophenol increased linearly with increasing nickel coating on iron. In general, increasing the degree of chlorine substitution on the phenol ring decreased the rate of dechlorination except for 2,6-DCP. Chlorophenols were dechlorinated to phenol via both stepwise as the major pathway and concerted mechanisms with minor contribution. The relative contribution of each reaction pathway is discussed through a model fitting.
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PMID:Kinetic studies of reductive dechlorination of chlorophenols with Ni/Fe bimetallic particles. 1761 67

Mixed hemimicelles solid-phase extraction (SPE) based on cetyltrimethylammonium bromide (CTAB)-coated nano-magnets Fe3O4 was investigated for the preconcentration of four chlorophenols (CPs) in environmental water samples prior to HPLC-spectrophotometry determination in this paper. By the rapid isolating (about 5 min) of Fe3O4 nanoparticles (NPs) through placing a Nd-Fe-B strong magnet on the bottom of beaker, the time-consuming preconcentration process of loading large volume sample in conversional SPE method with a column can be avoided. The unique properties of Fe3O4 NPs such as high surface area and strong magnetism were utilized adequately in the SPE process. This novel separation method produced a high preconcentration rate and factor. A comprehensive study of the adsorption conditions such as the Fe3O4 NPs zeta-potential, CTAB added amounts, pH value, standing time and maximal extraction volume was also presented. Under optimized conditions, four analytes of 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (TCP) and pentachlorophenol (PCP) were quantitatively extracted. The method was then used to determine four CPs in five real environmental water samples. High concentration factors (700) were achieved for each of the analytes, with observed detection limits ranging between 0.11 and 0.15 microg L(-1). The accuracy of method was evaluated by recovery measurements on spiked samples. Good recovery results (83-98%) with satisfactory relative standard deviation (RSD) were achieved. It is important to note that satisfactory preconcentration factors and extraction recoveries for the four CPs were obtained with only a little amount of Fe3O4 NPs (0.1g) and CTAB (60 mg). To the best of our knowledge, this was the first time a mixed hemimicelles SPE method based on Fe3O4 NPs magnetic separation had been used for the pretreatment of environmental water samples.
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PMID:Mixed hemimicelles solid-phase extraction based on cetyltrimethylammonium bromide-coated nano-magnets Fe3O4 for the determination of chlorophenols in environmental water samples coupled with liquid chromatography/spectrophotometry detection. 1817 1

Determination of trace chlorophenols (CPs) in environmental samples has been evaluated using liquid-phase microextraction (LPME) coupled with gas chromatography-mass spectrometry (GC-MS) without derivatization. The LPME procedure used to extract CPs from water involved 15 microL 1-octanol as acceptor solution in a 5.0 cm polypropylene hollow fiber with an inner diameter of 600 microm and a pore size of 0.2 microm. Under the optimal extraction conditions, enrichment factors from 117 to 220 are obtained. The obtained linear range is 1-100 ng mL(-1) with r(2)=0.9967 for 2,4-dichlorophenol (2,4-DCP); 1-100 ng mL(-1) with r(2)=0.9905 for 2,4,6-trichlorophenol (2,4,6-TCP); 5-500 ng mL(-1) with r(2)=0.9983 for 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP), and 10-1000 ng mL(-1) with r(2)=0.9929 for pentachlorophenol (PCP). The limits of detection range from 0.08 to 2 ng mL(-1), which is comparable with the reported values (12-120 ng mL(-1)). Recoveries of CPs in various matrices exceed 85% with relative standard deviations of less than 10%, except for PCP in landfill leachate. The applicability of this method was examined to determine CPs in environmental samples by analyzing landfill leachate, ground water and soil. The 2,4-DCP and 2,4,6-TCP detected in the landfill leachate are 6.68 and 2.47 ng mL(-1). The 2,4,6-TCP detected in ground water is 2.08 ng mL(-1). All the studied CPs are detected in contaminated soil. The proposed method is simple, low-cost, less organic solvent used and can potentially be applied to analyze CPs in complex environmental matrices.
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PMID:Evaluation of liquid-phase microextraction conditions for determination of chlorophenols in environmental samples using gas chromatography-mass spectrometry without derivatization. 1858 57

This study reports the feasibility of removing pentachlorophenol (PCP) by an acidogenic process in batch reactors. When the acidogenic sludge was first acclimated with 2,4,6-trichlorophenol (2,4,6-TCP) and developed 2,4,6-TCP dechlorinating activity, PCP could be ortho-dechlorinated to 3,4,5,-trichlorophenol (3,4,5-TCP) via 2,3,4,5-tetrachlorophenol as the intermediary. However, due to PCP's higher hydrophobicity and its higher expected Gibbs free energy yield, it was adsorbed to the sludge and dechlorinated preferentially to 2,4,6-TCP. This resulted in the inhibition of 2,4,6-TCP dechlorination. PCP removal under acidogenic condition was attributed to both reductive dechlorination and adsorption. At low PCP loads of 0.48micromoles/gMLVSS.d, dechlorination was the dominant removal mechanism (69% of total removal), while at the higher PCP load of 9.3micromoles/gMLVSS.d, adsorption was the main mechanism (82% of total removal). Attempts to induce meta or para position dechlorination of PCP failed when using meta position chlorophenols such as 2,3,6-TCP, 3,4,5-TCP and 3,5-DCP as the initial substrates. Overall, acidogenic biotreatment was an effective process in reducing PCP loads prior to downstream biological treatment.
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PMID:Pentachlorophenol dechlorination by an acidogenic sludge. 1869 30

A modified headspace liquid-phase microextraction (HS-LPME) method was studied for the extraction of chlorophenols (CPs) from aqueous samples with complicated matrices, before gas chromatographic (GC) analysis with electron capture detection (ECD). Microwave heating was applied to accelerate the evaporation of CPs into the headspace, and an external-cooling system was used to control the sampling temperature. Conditions influencing extraction efficiency, such as the LPME-solvent, the sampling position of LPME, the sampling temperature, microwave power, and irradiation time (the same as sampling time), sample pH, and salt addition were thoroughly optimized. Experimental results indicated that the extraction of CPs from a 10mL aquatic sample (pH 1.0) was achieved with the best efficiency through the use of 1-octanol as solvent, microwave irradiation of 167W, and sampling at 45 degrees C for 10min. The detections were linear in the concentration of 5.0-100microg/L for 2,4-dichlorophenol (2,4-DCP), and 0.5-10microg/L for 2,4,6-trichlorophenol (2,4,6-TCP), 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP) and pentachlorophenol (PCP). Detection limits were found to be 0.7, 0.04, 0.07, and 0.08microg/L for 2,4-DCP, 2,4,6-TCP, 2,3,4,6-TeCP, and PCP, respectively. A landfill leachate sample was analyzed with recovery between 83 and 102%. The present method was proven to serve as a simple, sensitive, and rapid procedure for CP analysis in an aqueous sample.
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PMID:Microwave-assisted headspace controlled temperature liquid-phase microextraction of chlorophenols from aqueous samples for gas chromatography-electron capture detection. 1876 Jul 97

Reductive dehalogenation of 2,4,6-trichlorophenol (2,4,6-TCP) by two types of high carbon iron filings (HCIF), HCIF-1 and HCIF-2 was studied in batch reactors. While the iron, copper, manganese and carbon content of the two types of HCIF was similar, the specific surface area of HCIF-1 and HCIF-2 were 1.944 and 3.418m(2)g(-1), respectively. During interaction with HCIF-1, 2,4,6-TCP adsorbed on HCIF-1 surface resulting in rapid reduction of aqueous phase 2,4,6-TCP concentration. However, reductive dehalogenation of 2,4,6-TCP was negligible. During interaction between 2,4,6-TCP and HCIF-2, both 2,4,6-TCP adsorption on HCIF-2, and 2,4,6,-TCP dechlorination was observed. 2,4,6-TCP partitioning between solid and aqueous phase could be described by a Freundlich isotherm, while 2,4,6-TCP dechlorination could be described by an appropriate rate expression. A mathematical model was developed for describing the overall interaction of 2,4,6-TCP with HCIF-2, incorporating simultaneous adsorption/desorption and dechlorination reactions of 2,4,6-TCP with the HCIF surface. 2,4-Dichlorophenol (2,4-DCP), 2-chlorophenol (2-CP) and minor amounts of 4-chlorophenol (4-CP) evolved as 2,4,6-TCP dechlorination by-products. The evolved 2,4-DCP partitioned strongly to the HCIF surface. 4-CP and 2-CP accumulated in the aqueous phase. No transformation of 2-CP or 4-CP to phenol was observed.
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PMID:Interaction of 2,4,6-trichlorophenol with high carbon iron filings: Reaction and sorption mechanisms. 1883 19

The sorption behaviour of 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), 2,3,4,5-tetrachlorophenol (2,3,4,5-TeCP) and pentachlorophenol (PCP) with an aquatic humic sorbent (HS) was examined in their single and mixed solutions at different acidities (pH 3, 5.5 and 7). The binding capacities and equilibrium coefficients (K(OC)) obtained were fairly close to the literature values but still underline HS's structural and steric influence on the sorption. The most acidic carboxylic (COOH) groups of the HS structure have unquestionably an essential role in the sorption. The amounts of different chlorophenols bound onto the constant quantity of the aquatic HS were in reality very low demonstrating that the amount of the dissolved organic carbon (DOC) in the environment plays a greater role than the value of K(OC). The ability of the aqueous phase to force chlorophenols to associate with the HS becomes at more neutral acidities weaker and weaker and other binding mechanisms become favoured in comparison to hydrogen or hydrophobic bonds. Sorption isotherms were constructed from sorption data, and conformity to a linear model, non-linear Freundlich equation and Langmuir equation was checked.
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PMID:Sorption behaviour of some chlorophenols in lake aquatic humic matter. 1896 25


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