Removal of Iron and Copper Ions and Phenol from Liquid Phase by Membrane Based on Carbonaceous Materials.

The present work reports an effective method for the removal of inorganic and organic pollutants using membranes based on different carbonaceous materials. The membranes were prepared based on cellulose acetate (18 wt. %), polyvinylpyrrolidone as a pore-generating agent (2 wt. %) and activated carbon (1 wt. %). Activated carbons were developed from residues after extraction of the mushroom Inonotus obliguus using microwave radiation. It has been demonstrated that the addition of activated carbon to the membranes resulted in alterations to their physical properties, including porosity, equilibrium water content and permeability. Furthermore, the chemical properties of the membranes were also affected, with changes observed in the content of the surface oxygen group. The addition of carbon material had a positive effect on the removal of copper ions from their aqueous solutions by the cellulose-carbon composites obtained. Moreover, the membranes proved to be more effective in the removal of copper ions than iron ones and phenol. The membranes were found to show higher effectiveness in copper removal from a solution of the initial concentration of 800 mg/L. The most efficient in copper ions removal was the membrane containing urea-enriched activated carbon.

Adsorption of Nitrogen Dioxide on Nitrogen-Enriched Activated Carbons.

The aim of this study was to obtain nitrogen-enriched activated carbons from orthocoking coal. The initial material was subjected to a demineralisation process. The demineralised precursor was pyrolysed at 500 °C and then activated with sodium hydroxide at 800 °C. Activated carbon adsorbents were subjected to the process of ammoxidation using a mixture of ammonia and air at two different temperature variants (300 and 350 °C). Nitrogen introduction was carried out on stages of demineralised precursor, pyrolysis product, and oxidising activator. The elemental composition, acid-base properties, and textural parameters of the obtained carbon adsorbents were determined. The activated carbons were investigated for their ability to remove nitrogen dioxide. The results demonstrated that the ammoxidation process incorporates new nitrogen-based functional groups into the activated carbon structure. Simultaneously, the ammoxidation process modified the acid-base characteristics of the surface and negatively affected the textural parameters of the resulting adsorbents. Furthermore, the study showed that all of the obtained carbon adsorbents exhibited a distinct microporous texture. Adsorption tests were carried out against NO2 and showed that the carbon adsorbents obtained were highly effective in removing this gaseous pollutant. The best sorption capacity towards NO2 was 23.5 mg/g under dry conditions and 75.0 mg/g under wet conditions.

A Study on the Adsorption of Rhodamine B onto Adsorbents Prepared from Low-Carbon Fossils: Kinetic, Isotherm, and Thermodynamic Analyses.

The aim of this study was to obtain a series of activated carbon samples by the chemical activation of low-rank coal. The precursor was impregnated with a NaOH solution. Activated carbons were characterized by determining their textural parameters and content of surface oxygen functional groups and by using an elemental analysis. The carbons were tested as potential adsorbents for the removal of liquid pollutants represented by rhodamine B. The effectiveness of rhodamine B removal from water solutions depended on the initial concentration of the dye, the mass of rhodamine B, and the pH and temperature of the reaction. The isotherm examination followed the Langmuir isotherm model. The maximum adsorption capacity of the rhodamine B was 119 mg/g. The kinetic investigation favored the pseudo-second-order model, indicating a chemisorption mechanism. The thermodynamic assessment indicated spontaneous and endothermic adsorption, with decreased randomness at the solid-liquid interface. The experiment revealed that a 0.1 M HCl solution was the most effective regenerative agent.

Catalysis of Indium Ion Electroreduction in the Presence of Acetazolamide in Chlorates(VII) Solutions with Varied Water Activity.

The influence of acetazolamide (ACT) on the kinetics and the mechanism of electroreduction of In(III) ions as a function of changes of the water activity was investigated using electrochemical methods (DC, SWV, CV and EIS, CV). The multi-step mechanism of the electroreduction process should take into account the dehydration step of indium ions and the presence of In-ACT (,,cap-pair" effect) active complexes, mediating electron transfer, located in the adsorption layer. Differences in the electrode mechanism in the presence of ACT were observed for higher chlorates(VII) concentrations (above 4 mol ⋅ dm-3 chlorates(VII)) reflected by a lack of step wise nature of the electrode process. The highest catalytic activity was observed in 4 mol ⋅ dm-3 chlorates(VII).

Removal of Methyl Red from Aqueous Solution Using Biochar Derived from Fennel Seeds.

In this study, fennel (Foeniculum vulgare) seeds were used as a precursor to obtain carbon adsorbents through physical activation with carbon dioxide and chemical activation by impregnating the precursor with sodium carbonate. The physical activation involved the carbonization of the precursor at a temperature of 600 °C for 60 min and activation at a temperature of 800 °C for 30 min with carbon dioxide. Chemical activation included impregnation of the precursor with sodium carbonate at a mass ratio of a precursor to activator of 1:2. The mixture was activated in a nitrogen atmosphere with a flow rate at a temperature of 700 °C for 45 min. The resulting biochar samples were washed with 5% hydrochloric acid and subsequently rinsed with boiling distilled water. The biochar adsorbents were characterized using low-temperature nitrogen adsorption-desorption isotherms, Boehm titration, and pH measurements of their aqueous extracts. The specific surface area of the obtained adsorbents ranged from 89 to 345 m2/g. Biochar adsorbents exhibit a predominance of acidic groups over basic groups on their surfaces. The sorption capacities of the obtained samples towards an aqueous solution of methyl red range from 26 to 135 mg/g. Based on adsorption studies, it was found that the adsorption of the dye on the obtained biochar materials follows a pseudo-second-order model. The Freundlich isotherm best describes the studied process, indicating the formation of a multilayer of adsorbate on the adsorbent surface. The efficacy of adsorption in aqueous solutions of methyl red was found to increase with the elevation of the process temperature. Moreover, thermodynamic studies have shown that the adsorption process is spontaneous and endothermic. Consequently, this work provides a description of the physicochemical parameters of two biochars obtained by physical and chemical activation of a little-studied precursor-fennel seeds-and studies on their potential use as adsorbents for contaminants from the aqueous phase.

Microwave-Assisted Fabrication of Fugus-Based Biocarbons for Malachite Green and NO2 Removal.

The aim of the current study was to produce biocarbons through the activation of carbon dioxide with the extraction residues of the fungus Inonotus obliquus. To achieve this goal, a microwave oven was used to apply three different activation temperatures: 500, 600, and 700 °C. Low-temperature nitrogen adsorption/desorption was employed to determine the elemental composition, acid-base properties, and textural parameters of the resulting carbon adsorbents. Subsequently, the produced biocarbons were evaluated for their efficiency in removing malachite green and NO2. The adsorbent obtained by activation of the precursor in 700 °C had a specific surface area of 743 m2/g. In the aqueous malachite green solution, the highest measured sorption capacity was 176 mg/g. Conversely, under dry conditions, the sorption capacity for NO2 on this biocarbon was 21.4 mg/g, and under wet conditions, it was 40.9 mg/g. According to the experimental findings, surface biocarbons had equal-energy active sites that interacted with the dye molecules. A pseudo-second-order kinetics model yielded the most accurate results, indicating that the adsorption of malachite green was driven by chemisorption. Additionally, the study demonstrates a clear correlation between the adsorption capacity of the biocarbons and the pH level of the solution, as it increases proportionately.

Microwave Heating for Synthesis of Carbonaceous Adsorbents for Removal of Toxic Organic and Inorganic Contaminants.

The residues obtained from the extraction of Inonotus obliquus fungus were used to produce carbonaceous adsorbents. The initial material was subjected to pyrolysis in a microwave oven. The adsorbents were characterized through elemental analysis, low-temperature nitrogen adsorption/desorption isotherms, and Boehm titration. The carbonaceous adsorbents were tested for the removal of NO2, methylene blue, and malachite green. The results indicated that the obtained carbonaceous adsorbents exhibited basic characteristics and possessed specific surface areas of 372 and 502 m2/g. The adsorption process of liquid contaminants was modeled using the single-layer Langmuir model. The maximum adsorption capacities were found to be 101 and 109 mg/g for methylene blue, and 75 and 77 mg/g for malachite green. The kinetic study demonstrated that the adsorption of methylene blue and malachite green was better described by a pseudo-second order model. The study affirmed that the adsorption of organic dyes onto the resultant carbonaceous adsorbents was both spontaneous and endothermic. The study also demonstrated that the presence of an air stream during the NO2 adsorption process and prehumidization of the adsorbent with humid air had a beneficial effect on the obtained sorption capacities. In conclusion, the study demonstrated that pyrolysis of the extraction residues from the fungus Inonotus obliquus yields highly effective, environmentally friendly, and cost-efficient carbonaceous adsorbents for the removal of both gaseous and liquid pollutants.

Removal of Methylene Blue and Methyl Red from Aqueous Solutions Using Activated Carbons Obtained by Chemical Activation of Caraway Seed.

In this study, activated carbons were produced through the chemical activation of caraway seeds using three different activators: Na2CO3, K2CO3, and H3PO4. A 1:2 weight ratio of precursor to activator was maintained in every instance. Comprehensive analyses were conducted on the resultant activated carbons, including elemental analysis, textural parameters determination, Boehm titration for surface oxygen functional groups, pH assessment of aqueous extracts, and quantification of ash content. The produced materials were subjected to adsorption tests for methylene blue and methyl red sodium salt from the liquid phase and the effects of adsorbent dosage, pH of the aqueous dye solution, process temperature, and adsorbent-adsorbate contact time on sorption capacity obtained. To characterize the adsorption model of the examined pollutants, both the Langmuir and Freundlich equations were employed. In addition, the sorption capacity of the obtained carbon materials against an iodine aqueous solution was assessed. The specific surface area of the obtained adsorbents ranged from 269 to 926 m2/g. By employing potassium carbonate to chemically activate the starting substance, the resulting activated carbons show the highest level of specific surface area development and the greatest sorption capacity against the tested impurities-296 mg/g for methylene blue and 208 mg/g for methyl red sodium salt. The adsorption rate for both dyes was determined to align with a pseudo-second-order kinetic model. The experimental adsorption data for methylene blue were well-described by the Langmuir model, whereas the Freundlich model was found to be congruent with the data pertaining to methyl red sodium salt.

Kinetics and Mechanism of In(III) Ions Electroreduction on Cyclically Renewable Liquid Silver Amalgam Film Electrode: Significance of the Active Complexes of In(III)-Acetazolamide.

The results of kinetic measurements revealed an accelerating effect of acetazolamide (ACT) on the multistep In(III) ions electroreduction in chlorates(VII) on a novel, cyclically renewable liquid silver amalgam film electrode (R-AgLAFE). The kinetic and thermodynamic parameters were determined by applying the DC polarography, square-wave (SWV) and cyclic voltammetry (CV), as well as electrochemical impedance spectroscopy (EIS). It was shown that ACT catalyzed the electrode reaction ("cap-pair" effect) by adsorbing on the surface of the R-AgLAFE electrode. The catalytic activity of ACT was explained as related to its ability to form active In(III)- acetazolamide complexes on the electrode surface, facilitating the electron transfer process. The active complexes constitute a substrate in the electroreduction process and their different structures and properties are responsible for differences in the catalytic activity. The determined values of the activation energy ΔH≠ point to the catalytic activity of ACT in the In(III) ions electroreduction process in chlorates(VII). Analysis of the standard entropy values ΔS0 confirm changes in the dynamics of the electrode process.

Microporous Biocarbons Derived from Inonotus obliquus Mushroom and Their Application in the Removal of Liquid and Gaseous Impurities.

Biocarbons were obtained by physical and chemical activation of the residue of the extraction of chaga fungi (Inonotus obliquus). The residue was subjected to heat treatment carried out in a microwave oven and in a quartz tubular reactor. The materials were characterized by elemental analysis, low-temperature nitrogen adsorption, determination of pH, and the contents of acidic and basic oxygen functional groups on the surface of biocarbons by the Boehm method. The final biocarbon adsorbents have surface areas varying from 521-1004 m2/g. The physical activation of the precursor led to a strongly basic character of the surface. Chemical activation of Inonotus obliquus promoted the generation of acid functional groups. All biocarbons were used for methyl red sodium salt adsorption from the liquid phase. The sorption capacities of biocarbons towards the organic dye studied varied from 77 to 158 mg/g. The Langmuir model was found to better describe the experimental results. The results of the kinetic analysis showed that the adsorption of methyl red sodium salt on the biocarbons followed the pseudo-second-order model. The acidic environment was conducive to the adsorption of the dye on the obtained biocarbons. Moreover, thermodynamic studies confirmed that the organic dye adsorption on the biocarbons was a spontaneous endothermic process. The biocarbons obtained were also tested as adsorbents of hydrogen sulfide in dry and wet conditions. The sorption capacities towards hydrogen sulfide varied in the range of 21.9-77.9 mg. The results have shown that the adsorption of hydrogen sulfide depends on the process conditions and the activation procedure of biocarbons (method of activation and thermochemical treatment of samples). It has been shown that the initial material used can be a new precursor for obtaining cheap and-more importantly-universal bioadsorbents characterized by high effectiveness in the removal of air and water pollutants.

Activation of Waste Materials with Carbon(IV) Oxide as an Effective Method of Obtaining Biochars of Attractive Sorption Properties towards Liquid and Gas Pollutants.

Biochars that are the subjects of this report have been obtained from the residue of supercritical extraction of common nettle seeds with CO2. The residue was subjected to direct activation with carbon(IV) oxide as an activator. The obtained biochars were found to have a specific surface area inthe range of 888-1024 m2/g and a basic surface. They were used for the adsorption of a liquid organic pollutant (methylene blue) and a gas inorganic pollutant (NO2). As follows from the test results, the biochars were able to adsorb 150-239 mg of the dye. The Langmuir model was found to better describe the adsorption experimental data, while the kinetics of the process was better described by the pseudo-second-order model. From the thermodynamic analysis, it was inferred that the adsorption of methylene blue from a water solution was an endothermic and spontaneous reaction. It was established that elevated temperature of activation and the presence of air stream during adsorption had a positive impact on the adsorption of NO2 by the biochars studied. The greatest sorption capacity of the biochars towards NO2 was 59.1 mg/g.

Biocarbons Obtained from Fennel and Caraway Fruits as Adsorbents of Methyl Red Sodium Salt from Water System.

The aim of this study was to prepare biocarbons by biomass activation with carbon(IV) oxide. Fennel and caraway fruits were used as the precursors of bioadsorbents. The impact of the precursor type and temperature of activation on the physicochemical properties of the obtained biocarbons and their interaction with methyl red sodium salt upon adsorption process have been checked. The obtained bioadsorbents were characterized by determination of-low temperature nitrogen adsorption/desorption, elemental analysis, ash content, Boehm titration, and pH of water extracts. The biocarbons have surface area varying from 233-371 m2/g and basic in nature with acidic/basic oxygen-containing functional groups (3.23-5.08 mmol/g). The adsorption capacity varied from 63 to 141 mg/g. The influence of different parameters, such as the effectiveness of methyl red sodium salt adsorption, was evaluated. The adsorption kinetics was well fitted using a pseudo-second-order model. The Freundlich model best represented the equilibrium data. The amount of adsorbed dye was also found to increase with the increasing temperature of the process.

Adsorption of Organic Compounds on Adsorbents Obtained with the Use of Microwave Heating.

Activated carbons were obtained by physical and chemical activation of the residue of supercritical extraction of green tea leaves. All the adsorbents obtained were characterized by: elemental analysis, low-temperature nitrogen adsorption, and the contents of acidic and basic oxygen functional groups on the surface of activated carbons by the Boehm method. The activated carbons were micro- or micro-mesoporous with well-developed surface area ranging from 520 to 1085 m2/g and total pore volume from 0.62 to 0.64 cm3/g. The physical activation of the precursor led to the strongly basic character of the surface. Chemical activation with 50% solution of H3PO4 of the residue of supercritical extraction of green tea leaves promoted the generation of acidic functional groups. All adsorbents were used for methylene blue and methyl red adsorption from the liquid phase. The influence of the activation method, pH of the dye solution, contact time of adsorbent with adsorbate, the temperature of adsorption, and rate of sample agitation on the effectiveness of organic dyes removal was evaluated and optimized. In the process of methylene blue adsorption on adsorbents, an increase in the sorption capacity was observed with increasing pH of the adsorbate, while in the process of methyl red adsorption, the relation was quite the reverse. The adsorption data were analyzed assuming the Langmuir or Freundlich isotherm models. The Langmuir model better described the experimental results, and the maximum sorption capacity calculated for this model varied from 144.93 to 250.00 mg/g. The results of the kinetic analysis showed that the adsorption of organic dyes on activated carbon was following the pseudo-second-order model. The negative values of the Gibbs free energy indicate the spontaneous character of the process.

Carbon-Silica Composite as Adsorbent for Removal of Hazardous C.I. Basic Yellow 2 and C.I. Basic Blue 3 Dyes.

Treatment of wastewaters containing hazardous substances such as dyes from the textile, paper, plastic and food industries is of great importance. Efficient technique for the removal of highly toxic organic dyes is adsorption. In this paper, adsorptive properties of the carbon-silica composite (C/SiO2) were evaluated for the cationic dyes C.I. Basic Blue 3 (BB3) and C.I. Basic Yellow 2 (BY2). The sorption capacities were determined as a function of temperature (924.6-1295.9 mg/g for BB3 and 716.3-733.2 mg/g for BY2 at 20-60 °C) using the batch method, and the Langmuir, Freundlich and Temkin isotherm models were applied for the equilibrium data evaluation using linear and non-linear regression. The rate of dye adsorption from the 100 mg/L solution was very fast, after 5 min. of phase contact time 98% of BB3 and 86% of BY2 was removed by C/SiO2. Presence of the anionic (SDS), cationic (CTAB) and non-ionic (Triton X-100) surfactants in the amount of 0.25 g/L caused decrease in BB3 and BY2 uptake. The electrokinetic studies, including determination of the solid surface charge density and zeta potential of the composite suspensions in single and mixed adsorbate systems, were also performed. It was shown that presence of adsorption layers changes the structure of the electrical double layer formed on the solid surface, based on the evidence of changes in ionic composition of both surface layer and the slipping plane area. The greatest differences between suspension with and without adsorbates was obtained in the mixed dye + SDS systems; the main reason for this is the formation of dye-surfactant complexes in the solution and their adsorption at the interface.

Electroreduction of Bi(III) Ions at a Cyclically Renewable Liquid Silver Amalgam Film Electrode in the Presence of Methionine.

The catalytic influence of methionine (Mt) on the electroreduction of Bi(III) ions on the novel, cyclically renewable liquid silver amalgam film electrode (R-AgLAFE) in a non-complexing electrolyte solution was examined. The presence of methionine leads to a multistep reaction mechanism, where the transfer of the first electron is the rate limiting step, which is the subject of catalytic augmentation. The catalytic activity of methionine is a consequence of its ability to remove water molecules from the bismuth ion coordination sphere, as well as to form active complexes on the electrode surface, facilitating the electron transfer process.

Synthesis and characterization of the thermally reduced graphene oxide in argon atmosphere, and its application to construct graphene paste electrode as a naptalam electrochemical sensor.

New insight into the preparation of sensitive carbon-based electrochemical electrode is provided by examining the properties of thermally reduced graphene oxide (TRGO). In this paper, TRGO was prepared by thermal reduction of graphene oxide (GO) in argon atmosphere, and characterized by Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), selected area electron diffraction (SAED), and atomic force microscopy (AFM). Results showed that thermal reduction in argon was effective to remove oxygen-containing functional groups in GO, and graphene sheets were obtained. Furthermore, TRGO was used to prepare thermally reduced graphene oxide paste electrode (TRGOPE) which showed excellent conductivity and fast electron transfer kinetics confirmed by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The electrode was applied to determination of the pesticide naptalam (Nap) in square-wave voltammetric (SWV) mode. The corresponding current at approx. +1.0 V increased linearly with the Nap concentration within two linear dynamic ranges (LDR) of 0.1-1.0 µmol L-1 (LDR1) and 1.0-10.0 µmol L-1 (LDR2). The limits of detection (LOD) and quantification (LOQ) for Nap were calculated as 0.015 µmol L-1 and 0.051 µmol L-1, respectively. In comparison to the carbon paste electrode (CPE) the results showed that the TRGOPE possesses advantages in terms of linearity, sensitivity and detectability.

Improved electroanalytical characteristics for the determination of pesticide metobromuron in the presence of nanomaterials.

In the present work, bare ultra trace graphite electrode (UTGE), UTGE modified with multi-walled carbon nanotubes (UTGE-MWCNTs), and UTGE modified with graphene nanoplatelets (UTGE-GNPs) were considered as working electrodes. For the first time, the UTGEs were modified with MWCNTs and GNPs by simple and fast drop-casting approach (the whole procedures take no more times than ca. 30 min). The comprehensive microscopic and electrochemical characterization of the unmodified and the modified UTGEs was conducted by means of atomic force microscopy (AFM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) techniques. The prepared electrodes were further applied for the analytical purposes, and the procedures for the square-wave voltammetric (SWV) determination of pesticide metobromuron (Mbn) using the bare UTGE, the UTGE-MWCNTs, and the UTGE-GNPs were developed. For the first time, this compound was electrochemically investigated. The SWV measurements were performed in Britton-Robinson buffer (B-R) solution at pH 2.0 as a supporting electrolyte. SWV parameters, i.e. amplitude, frequency, and step potential, were optimized. The linear relationships between peak current vs. increasing concentrations of Mbn were defined using the bare UTGE, the UTGE-MWCNTs, and the UTGE-GNPs, and the limits of detection were calculated (0.13, 0.11, 0.048 µmol L-1, respectively). The analytical parameters determined from calibration curves indicate similar sensitivity on all tested electrodes, however, the widest linearity range as well as the lowest LOD and LOQ values were achieved on the UTGE modified with GNPs. The utility of the proposed method with the UTGE-GNPs was verified by the quantitative analysis of Mbn in soil samples with satisfactory results (recovery of 99.1%). Furthermore, the impact of possible interferences was tested and evaluated, and obtained results proved good selectivity of the proposed method.

ß-Cyclodextrins incorporated multi-walled carbon nanotubes modified electrode for the voltammetric determination of the pesticide dichlorophen.

In this work, a glassy carbon electrode modified with ß-cyclodextrins and multi-walled carbon nanotubes (ß-CDs/MWCNTs/GCE) was constructed and applied for the square-wave adsorptive stripping voltammetric (SWAdSV) determination of the pesticide dichlorophen (Dcp). For the first time, this compound was electrochemically investigated. The voltammetric measurements were conducted in phosphate buffer (PBS) at pH 6.5 as a supporting electrolyte, and SWAdSV technique parameters were optimized. A linear calibration curve in the wide concentration range from 5.0 × 10-8molL-1 to 2.9 × 10-6molL-1 was obtained. Excellent analytical performance in terms of limit of detection (LOD) of 1.4 × 10-8molL-1 was achieved. The utility of the proposed method was verified by the quantitative analysis of Dcp in Pilica River water samples with satisfactory results. The characterization of modified electrodes was conducted by means of atomic force microscopy (AFM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). Moreover, in this work, the dissociation constants (pKa) of Dcp using potentiometric pH titration were estimated. The stoichiometry of the Dcp-ß-CDs inclusion complex formed in solution was determined by proton nuclear magnetic resonance (1H NMR) spectroscopy, and a binding constant (ß2) was estimated from NMR titration studies.

Electrochemical determination of closantel in the commercial formulation by square-wave adsorptive stripping voltammetry.

ABSTRACT: In this paper, the square-wave adsorptive stripping voltammetric (SWAdSV) determination of the veterinary drug closantel using a renewable silver amalgam film electrode (Hg(Ag)FE) is presented. As observed in SWAdSV, closantel provided one well-shaped reduction peak suitable for analytical purposes at potential ca. -1.4 V in the Britton-Robinson (B-R) buffer at pH 7.0. At optimal conditions, the SWAdSV response of Hg(Ag)FE for determining closantel was linear over two concentration ranges of 5.0 × 10-8 to 2.0 × 10-7 mol dm-3 and 2.0 × 10-7 to 1.2 × 10-6 mol dm-3 with a detection limit of 1.1 × 10-8 mol dm-3. In addition, a relevance of the developed SWAdSV method was successfully verified by the quantitative analysis of closantel in the commercial formulation Closamectin Pour-On with satisfactory results (RSD = 5.8%, recovery = 101.8%). The results showed that the developed procedure can be adequate for screening purposes. Also, the electrochemical behavior of closantel was characterized by cyclic voltammetry, and it was found that closantel exhibited a quasi-reversible behavior with cathodic peak on the forward scan at ca. -1.4 V and anodic peak on the reverse scan at ca. -1.35 V vs. Ag/AgCl in B-R buffer, pH 7.0. As the obtained results showed that the electrode mechanism of closantel is controlled by the adsorption, the effect of adsorption was studied using the electrochemical impedance spectroscopy technique.

Improved electroanalytical characteristics for flumetralin determination in the presence of surface active compound.

ABSTRACT: The use of square wave voltammetry (SWV) and square wave adsorptive stripping voltammetry (SWAdSV) in conjunction with a cyclic renewable silver amalgam film electrode for the determination of flumetralin is presented. Poor separation of two overlapped reduction peaks is significantly improved when hexadecyltrimethylammonium bromide is used as a component of the supporting electrolyte solution (together with BR buffer pH 9.5). The SW technique parameters were investigated and found optimal as follows: frequency 50 Hz, amplitude 40 mV, and step potential 5 mV. Accumulation time and potential were studied to select the optimal conditions in adsorptive voltammetry. The analytical curve was linear for the flumetralin concentration range from 1.0 × 10-6 to 1.0 × 10-5 mol dm-3 and from 5.0 × 10-9 to 1.0 × 10-7 mol dm-3 for SWV and SWAdSV, respectively. Detection limit of 6.5 × 10-10 mol dm-3 was calculated for accumulation time 60 s at -0.2 V. The repeatability of the method was determined at a flumetralin concentration level equal to 5.0 × 10-9 mol dm-3 and expressed as %RSD = 5.0% (n = 6). The proposed method was applied and validated successfully by studying the recovery of herbicide content in spiked environmental samples.