Development,validation and application of an HPLC method for phenol electrooxidation products in the presence of chloride

A high-performance liquid chromatography (HPLC) method was developed and validated to determine phenol and potential intermediates from hydroxylation (hydroquinone, benzoquinone, catechol) and hypochlorination (2-chlorophenol, 3-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol, 2,6-dichlorophenol, 2,3,6-trichlorophenol, 2,4,5-trichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol) pathways during electrooxidation in the presence of chloride. A Hypersil ODS column (150 mm L × 4.6 mm I.D.) was used for the separation. The best separation was achieved when using a time variant gradient between a water mobile phase (with 0.1% formic acid adjusted to pH 3.0 with 0.1 mM sulfuric acid) and an organic phase (90:5:5 by volume mixture of acetonitrile:methanol:acetic acid). The flow rate was 0.8 mL min^?1 and UV absorbance was monitored at 270, 280, 290 and 300 nm, choosing the wavelength of strongest response for each compound. The intra- and inter-day accuracy and precision were tested using five replicates each day on three consecutive days.     

Synthesis of porous vinylnaphthalene/divinylnaphthalene copolymers and their sorptive properties towards phenol and its derivatives

Four porous vinylnaphthalene/divinylnaphthalene (VN/DVN) polymers having three different nominal crosslinking degrees (60, 80 and 100 wt.%) have been synthesized using the suspension polymerization method in the presence of toluene and decane.The use of various crosslinking levels and inert diluents was aimed at changing the extent of polymeric network-diluent interactions. The resultant polymers have specific surface area in the range 450-700 m²/g depending on the DVN content. Two sets of pores were detected in all resins: one with the diameter of ≈2 nm and the second one in the range of 30-40 nm. Their sorptive properties have been studied using dilute (0.5 mmol/l) solutions of phenol and its derivatives (o-chlorophenol, 2-methylphenol, o-nitrophenol, m-nitrophenol and p-nitrophenol). It has been found that sorption, at low equilibrium concentration, follows the order: o-nitrophenol > o-chlorophenol > m-nitrophenol > o-methylphenol > p-nitrophenol > phenol. Full characteristics of the porous structure of resultant polymers was obtained by nitrogen adsorption at 77 K and their surface properties analyzed using Inverse Gas Chromatography.     

Structure Sensitivity in the Hydrodechlorination of Chlorophenols

The gas phase hydrodechlorination of methanolic and mixed methanol/water solutions of 2-chlorophenol, 2,6-dichlorophenol, 2,4,5-trichlorophenol and pentachlorophenol has been studied at 573 K over nickel/silica catalysts of varying (1.5–20.3 wt.% Ni) nickel loading. Each catalyst was 100% selective in promoting hydrodechlorination: the variation of catalytic activity and selectivity with time-on-stream is illustrated and catalyst deactivation is addressed. Dechlorination is quantified in terms of specific rate constants, phenol selectivity/yield and chlorine removal efficiencies. Increasing the nickel loading resulted in a marked increase in dechlorination efficiency while the introduction of water into the feed lowered the activity.     

Use of polymeric sorbents for the off-line preconcentration of priority pollutant phenols from water for high-performance liquid chromatographic analysis

The use of porous polymeric minicolumns for the determination of phenols from the U.S. Environmental Priority Pollutant List was studied. For the off-line preconcentration of priority pollutant phenols from water by solid-phase extraction, minicolumns packed with 1,4-di(methacryloyloxymethyl)naphthalene-divinylbenzene copolymer and Amberlite XAD-4 were used. In order to compare the sorption properties of these polymeric sorbents, the recoveries and breakthrough volumes of phenol, p-nitrophenol, 2,4-dinitrophenol, o-chlorophenol, o-nitrophenol, 2,4-dimethylphenol, 4-chloro-m-cresol, 4,6-dinitro-o-cresol, 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol were studied.     

Membrane-assisted solvent extraction of seven phenols combined with large volume injection-gas chromatography-mass spectrometric detection

Membrane-assisted solvent extraction (MASE) was applied for the determination of seven phenols (phenol, 2-chlorophenol, 2,4-dimethylphenol, 2,4-dichlorophenol, 4-chloro-3-methylphenol, 2,4,6-trichlorophenol and pentachlorophenol) with log Kow (octanol-water-partition-coefficient) between 1.46 (phenol) and 5.12 (pentachlorophenol) in water. The extraction solvents cyclohexane, ethyl acetate and chloroform were tested and ethyl acetate proved to be the best choice. The optimisation of extraction conditions showed the necessity of adding 5 g of sodium chloride to each aqueous sample to give a saturated solution (333 g/L). The pH-value of the sample was adjusted to 2 in order to convert all compounds into their neutral form. An extraction time of 60 min was found to be optimal. Under these conditions the recovery of phenol, the most polar compound, was 11%. The recoveries of the other analytes ranged between 42% (2-chlorophenol) and 98% (2,4-dichlorophenol). Calibration was performed using large volume injection (100 microL injection volume). At optimised conditions the limits of detection were between 0.01 and 0.6 microg/L and the relative standard deviation (n = 3) was on average about 10%. After the method optimisation with reagent water membrane-assisted solvent extraction was applied to two contaminated ground water samples from the region of Bitterfeld in Saxony-Anhalt, Germany. The results demonstrate the good applicability of membrane-assisted solvent extraction for polar analytes like phenols, without the necessity of derivatisation or a difficult and time-consuming sample preparation.     

Detection and determination of chlorophenols and chlorophenoxyacetic acids by instrumental analysis

A quantitative method for the determination of chlorophenols and chlorophenoxyacetic acids in aqueous solutions is described. The samples investigated contained 2-chlorophenol, 2,4-dichlorophenol, 2,6-dichlorophenol, 2,4,6-trichlorophenol and their phenoxyacetic acid derivatives. The total amount of chlorophenols is determined by spectrophotometry, the ratio of individual chlorophenols by gas chromatography and the total quantity of phenoxyacetic acids by acidimetric titration. The determinations are carried out after extraction with diethyl ether, carbon tetrachloride and petroleum ether, respectively.     

Derivative spectrophotometry in the analysis of mixtures of phenols and herbicides

Derivative spectrophotometry (zero-crossing technique) was applied to the determination of selected phenols and herbicides in two-component mixtures. Methyl- and chlorophenols (3-methylphenol, 2,3- and 3,4-dimethylphenol, 2,5-, 2,6- and 3,4-dichlorophenol and 2,4,5-trichlorophenol) and triazine, uracil and urea herbicides (simazine, propazine, hexazinone, bromacil and metoxuron) were examined. The RSD values ranged between 0.05 and 4% and the recoveries obtained were between 97 and 110%. The developed derivative spectrophotometric method was also applied as a complementary technique for the separation of overlapping peaks of sample compounds obtained by HPLC with diode-array detection. Metoxuron and 3-methylphenol, metoxuron and 2,5-dichlorophenol and simazine and 2,6-dichlorophenol were determined simultaneously by this method at the level of 1 x 10(-3) g l-1.     

Oxidative degradation of phenols in sono-Fenton-like systems upon high-frequency ultrasound irradiation

The kinetics of oxidative degradation of phenol and chlorophenols upon acoustic cavitation in the megahertz range (1.7 MHz) is studied experimentally in model systems, and the involvement of in situ generated reactive oxygen species (ROSs) is demonstrated. The phenols subjected to high frequency ultrasound (HFUS) are ranked in terms of their rate of conversion: 2,4,6-trichlorophenol > 2,4-dichlorophenol ~ 2-chlorophenol > 4-chlorophenol ~ phenol. Oxidative degradation upon HFUS irradiation is most efficient at low concentrations of pollutants, due to the low steady-state concentrations of the in situ generated ROSs. A dramatic increase is observed in the efficiency of oxidation in several sonochemical oxidative systems (HFUS in combination with other chemical oxidative factors). The system with added Fe²⁺ (a sono-Fenton system) derives its efficiency from hydrogen peroxide generated in situ as a result of the recombination of OH radicals. The S₂O₈^2-/Fe²⁺/HFUS system has a synergetic effect on substrate oxidation that is attributed to a radical chain mechanism. In terms of the oxidation rates, degrees of conversion, and specific energy efficiencies of 4-chlorophenol oxidation based on the amount of oxidized substance per unit of expended energy the considered sonochemical oxidative systems form the series HFUS < S₂O₈^2-/HFUS < S₂O₈^2-/Fe²⁺/HFUS.     

Narrow-band irradiation of a homologous series of chlorophenols on TiO2: charge-transfer complex formation and reactivity

The goal of this research was to investigate the formation and reactivity of charge-transfer complexes (CTCs) among a homologous series of chlorophenols on TiO2. We previously showed that 2,4,5-trichlorophenol (245TCP) forms a CTC with Degussa P25, a commercial preparation of TiO2. Here, we probe how light energy influences reactivity and product formation. Slurries of P25 containing 245TCP were irradiated at 360, 400, 430, 480, and 550 nm. At each wavelength, the amount of transformation of 245TCP correlates to the diffuse-reflectance absorbance of a 245TCP/P25 system, supporting the CTC as the cause of reaction. In addition, polymeric products are formed only under wavelengths that excite the CTC, indicating a different reaction mechanism for the CTC than for bandgap excitation of TiO2. We also found a higher quantum efficiency for CTC reactivity than for bandgap activation of the catalyst, suggesting that the photocatalytic efficiency and selectivity can be improved for certain compounds by designing catalytic materials that form CTCs with them. Furthermore, to determine how chlorine substitution patterns affected adsorption and sub-bandgap reactivity, P25 slurries containing phenol, 4-chlorophenol, 2,4-dichlorophenol, or 2,4,6-trichlorophenol were probed following dark contact or irradiation at 360, 430, or 550 nm. With respect to the extent of adsorption, complexation, reaction, and polymerization on P25, the behavior of 245TCP far exceeded that of the other chlorophenols. Among these chlorophenols, only 2,4-dichlorophenol produced a polymeric product. 245TCP is unique among this family of chlorophenols, which we attribute to a chlorine arrangement that leads to a favorable orbital overlap with TiO2 and sterically permits coupling reactions. Our results demonstrate the critical role that charge-transfer complexation can play in determining the rates and products of photocatalytic reactions.     

Synthesis and analytical properties of a novel columnar metallomesogenic polymer

A metallomesogenic side-chain polymer with copper carboxylato discotic units in stacks prepared by covalent bonding of 14-pentadecenoic acid, stearic acid and poly(methylhydrosiloxane) is described. The physico-chemical and thermal properties of both monomeric and polymeric metallomesogens were determined by elemental analysis, IR, polarizing optical microscopy, thermal gravimetric analysis and differential scanning calorimetry. The polymeric states showed a discotic lamellar phase at 50-95 degrees C and an ordered discotic hexagonal phase at 95-200 degrees C. By dynamic coating, the metallomesogenic polymer was crosslinked to the capillary wall via benzoyl peroxide. The wall-coated capillary columns (15 m x 0.25 mm I.D.) were used for the separation of phenols. Factors affecting the retention and the sample selectivity were examined. Van 't Hoff plots as a function of temperature indicated that phase transitions were occurring. Thermodynamic properties of the analytes in this system were also studied. For the determination of a mixture of 3-aminophenol, 2-chlorophenol, 2-nitrophenol, 4-nitrophenol, o-methylphenol, m-methylphenol, p-methylphenol, 2,4-dichlorophenol, 2,4-dimethylphenol, 2,4-dinitrophenol, 2,4,6-trichlorophenol, 2,4,6-trimethylphenol, 4-bromophenol, 3-methyl-4-chlorophenol, pentachlorophenol, and unsubstituted phenol, the calibration graphs for most phenols were linear over the range of 10-1000 microg ml(-1) and the mass detection limits were in the ng range based on three times standard deviation of seven measurements of the lowest peak that could be detected.     

A comparison between positive and negative ion modes in thermospray liquid chromatography-mass spectrometry for the determination of chlorophenols and herbicides

Summary Positive and negative ion modes (Pl and NI, respectively) have been employed for the characterization of 2,4-dichlorophenol, 2,4,5-trichlorophenol, pentachlorophenol, Linuron and Cyanazine in thermospray (TSP) liquid chromatography-mass spectrometry (LC-MS). The PI mode showed no response when 200 ng of the different chlorophenols were injected, while for Linuron and Cyanazine high signals were obtained with [M+NH₄]⁺ and [M+acetic acid]⁺ ions as base peaks, respectively. With the NI mode, the base peak usually corresponds to the [M−H]⁻ ion, with better sensitivities for the chlorophenols than for the herbicides. The chloride adduct [M+Cl]⁻ ion was also obtained for 2,4,5-trichlorophenol and for Linuron. Although the PI mode is more sensitive than the NI mode for the two herbicides, the combination of both ionization modes offers complementary structural information for characterizing such compounds in TSP LC-MS.     

In-capillary solid-phase extraction-capillary electrophoresis for the determination of chlorophenols in water

A novel CE method combined with SPE in a single capillary was developed for analysis of chlorophenols in water. A frit of 0.5 mm was first made by a sol-gel method, followed by packing a SPE sorbent in the inlet end of the capillary. Two phenol derivatives, 2,4-dichlorophenol and 2,4,5-trichlorophenol, were used as the model compounds. By loading sample solutions into the capillary, the two chlorophenols were extracted into the sorbent. They were desorbed by injecting only about 4 nL of methanol. Finally, the analytes were separated by conventional CE. The technique provided a concentration enhancement factor of over 4000-fold for both chlorophenols. The detection limits (S/N = 3) of 2,4-dichlorophenol and 2,4,5-trichlorophenol were determined to be 0.1 ng/mL and 0.07 ng/mL, respectively. For replicate analyses of 5 ng/mL of 2,4-dichlorophenol, within-day and between-day RSDs of migration time, peak height and peak area were in the range of 1.8-2.0%, 4.0-4.4% and 4.1-4.6%, respectively. The method shows wide linear range, acceptable reproducibility and excellent sensitivity, and it was applied to the analyses of spiked river water samples. The capillary packed with the SPE sorbents can be used for more than 400 runs without performance deterioration.     

酚类在芳烃溶剂中的缔合溶液热力学

用凝固点降低法测量了对甲酚、间甲酚、邻甲酚、2,4-二甲酚、2,6-二甲酚以及对甲酚+间甲酚、对甲酚+邻甲酚、间甲酚+邻甲酚、2,4-二甲酚+2,6-二甲酚的1:1摩尔比混合物等为溶质, 溶剂为苯或对二甲苯的活度系数, 用Wiehe-Bagley型的连续缔合模型对数据进行了处理, 得到了各种酚的自缔合常效K_A. 在同一溶剂中, K_A依下列顺序减小: 对甲酚>间甲酚>邻甲酚; 2,4-二甲酚>2,6-二甲酚. 各混合酚的表观K_A 介于两种纯酚的K_A之间.     

Photodegradation of chlorophenolic compounds using zinc oxide as photocatalyst: experimental and theoretical studies

Zinc oxide nanoparticles were synthesized via the sol?Cgel method. The structures of the obtained nanoparticles were investigated by X-ray diffraction. The photocatalytic degradation of chlorophenolic compounds, namely 2-chlorophenol (CP), 2,4-dichlorophenol (DCP) and 2,4,6-trichlorophenol (TCP), was carried out using ZnO nanoparticles under solar intensity of 20?C26?W?m^?2. The photocatalytic degradation efficiency of TCP?<?DCP?<?CP was found. The adsorption energies of the chlorophenolic compounds with ZnO catalyst were calculated from quantum chemical molecular dynamic model and found to increase in the order of TCP?<?DCP?<?CP.     

Potentiometric study of the distribution equilibria of phenols between 1.0 moldm−3 NaCl and organic solvents at 25 °C

The potentiometric determination of the distribution coefficient of phenol, 2-chlorophenol, 2-nitrophenol, 2,4-dichlorophenol and 2-methyl-phenol between 1.0 mol dm^–3 NaCl and five different organic solvents at 25 °C is presented. An automated potentiometric system was used and the determination of the constants was carried out using both graphical and numerical methods. The relevance of this study for the development of supported liquid membrane (SLM) recovery systems is discussed.     

Trace level determination of phenols as pentafluorobenzyl derivatives by gas chromatography-negative-ion chemical ionization mass spectrometry.

A method for the trace level determination of 11 phenols as pentafluorobenzyl (PFB) derivatives by gas chromatography-mass spectrometry (GC-MS) with negative-ion chemical ionization (NICI) is described. First, the conditions for the PFB derivatisation of phenols were optimized and were found to be reaction temperature 80 degrees C and reaction time 5 h. Second, the detection limits using selected ion monitoring (SIM) were compared between trimethylsilylated (TMS) derivatives in the electron ionization (EI) mode and PFB derivatives in the NICI mode. The responses for the PFB derivatives in the NICI mode were 3.3-61 times higher than those of the TMS derivatives in the EI mode. The instrumental detection limits using NICI-SIM ranged from 2.6 to 290 fg. This method was applied to the analysis of phenols in river water using solid-phase extraction. The recoveries of the phenols from a river water sample spiked with standards at 100 ng l-1 with 2-chlorophenol, 4-chloro-3-methylphenol and pentachlorophenol and at 1000 ng l-1 with phenol, 2,4-dimethylphenol, 2,4-dichlorophenol, 2-nitrophenol, 2,4,6-trichlorophenol and 4-nitrophenol were 81.2-106.3% (RSD 5.1-8.0%), except for 2-methyl-4,6-dinitrophenol and 2,4-dinitrophenol, for which the recoveries were 5.8 and 4.2%, respectively, because water contained in the acetone eluate interfered with the derivatisation of these compounds with two electrophilic nitro groups.     

ADSORPTION CHARACTERISTICS OF CHLOROPHENOLS FROM AQUATIC SYSTEMS BY HYPERCROSSLINKED RESINS MODIFIED WITH BENZOYL GROUP

A hypercrosslinked polymeric adsorbent （ZH-03） for adsorbing and removing chlorophenolic compounds from their aqueous solutions was studied, including the static adsorption. The equilibrium adsorption data were fit to Freundlich adsorption isothermic models to evaluate the model parameters. Thermodynamic studies on the adsorption of chlorophenolic compounds on ZH-03 indicated that there were chemisorption transitions for 2,4,6-trichlorophenol and physical adsorption processes for 2-chlorophenol and 2,6-chlorophenol, and ZH-03 showed the homogeneous nature of the adsorbent surface. Column adsorption for chlorophenols wastewater shows the advantages of the ZH-03 adsorbent for adsorbing the following chlorophenolic compounds as 2-chlorophenol, 2,6-dichlorophenol and 2,4,6-trichlorophenol. Sodium hydroxide was used for desorpting chlorophenols from ZH-03 and showed excellent performance.     

改进的五氟苄基溴衍生化反应测定水中酚类化合物

建立了气相色谱-质谱法测定水中6种酚类化合物(2,6-二氯酚、2,4-二氯酚、2,4,6-三氯酚、2,4,5-三氯酚、2,3,4,6-四氯酚和五氯酚)的方法.样品经二氯甲烷-乙酸乙酯混合溶剂萃取后,用旋转蒸发浓缩至1 mL,加入五氟苄基溴进行改进版衍生化反应,产物用DB-5 mS毛细管柱分离,采用选择离子监测模式测定....     

Characterization of a Novel Laccase LAC-Yang1 from White-Rot Fungus Pleurotus ostreatus Strain Yang1 with a Strong Ability to Degrade and Detoxify Chlorophenols

In this study, a laccase LAC-Yang1 was successfully purified from a white-rot fungus strain Pleurotus ostreatus strain yang1 with high laccase activity. The enzymatic properties of LAC-Yang1 and its ability to degrade and detoxify chlorophenols such as 2,6-dichlorophenol and 2,3,6-trichlorophenol were systematically studied. LAC-Yang1 showed a strong tolerance to extremely acidic conditions and strong stability under strong alkaline conditions (pH 9–12). LAC-Yang1 also exhibited a strong tolerance to different inhibitors (EDTA, SDS), metal ions (Mn²⁺, Cu²⁺, Mg²⁺, Na⁺, K⁺, Zn²⁺, Al³⁺, Co²⁺, and metal ion mixtures), and organic solvents (glycerol, propylene glycol). LAC-Yang1 showed good stability in the presence of Mg²⁺, Mn²⁺, glycerol, and ethylene glycol. Our results reveal the strong degradation ability of this laccase for high concentrations of chlorophenols (especially 2,6-dichlorophenol) and chlorophenol mixtures (2,6-dichlorophenol + 2,3,6-trichlorophenol). LAC-Yang1 displayed a strong tolerance toward a variety of metal ions (Na²⁺, Zn²⁺, Mn²⁺, Mg²⁺, K⁺ and metal ion mixtures) and organic solvents (glycerol, ethylene glycol) in its degradation of 2,6-dichlorophenol and 2,3,6-trichlorophenol. The phytotoxicity of 2,6-dichlorophenol treated by LAC-Yang1 was significantly reduced or eliminated. LAC-Yang1 demonstrated a good detoxification effect on 2,6-dichlorophenol while degrading this compound. In conclusion, LAC-Yang1 purified from Pleurotus ostreatus has great application value and potential in environmental biotechnology, especially the efficient degradation and detoxification of chlorophenols.     

Determination of 2,6-Dichlorophenol by Surface-Enhanced Raman Scattering with Molecular Imprinting

A novel method has been reported for 2,6-dichlorophenol using surface-enhanced Raman scattering (SERS). SiO₂/gold composites were selected as the SERS substrates to provide the response of gold nanoparticles. Molecular imprinting was subsequently used for the development of a specific detector to 2,6-dichlorophenol with precipitation polymerization. The molecularly imprinted polymer provided sensitive and selective SERS detection for the determination of 2,6-dichlorophenol. The intensity and concentration obeyed a linear relationship from 1?×?10^?5 to 1?×?10^?9?mol?L^?1 2,6-dichlorophenol. The sensitivity of SERS with the molecularly imprinted polymers provides a promising approach for practical analysis.