Platinized agarose microspheres as a new modifier in graphite paste electrodes for the electrochemical determination of 4-aminophenol.

In the environment, 4-aminophenol (4-AP) is present as a highly toxic compound and water pollutant. In this study, platinized agarose microspheres (PtAM) were used for the first time, for the preparation of a novel, modified graphite paste electrode (GPE/PtAM) for the electrochemical determination of 4-AP. PtAM was characterized using transmission electron microscopy, field emission scanning electron microscopy and energy dispersive X-ray analysis. The electrochemical response characteristics of GPE/PtAM towards 4-AP were investigated via electrochemical impedance spectroscopy, cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The value of the charge transfer resistance obtained for GPE/PtAM was 27.3 Ω. Microscopic surface areas and the surface concentration of the electroactive species for GPE/PtAM were calculated to be 0.077 cm2 and 1.13 × 10-3 mol cm-2, respectively. The electron transfer coefficient, diffusion coefficient and standard heterogeneous rate constants of 4-AP were calculated as 0.274, 4.56 × 10-4 cm2 s-1, and 3.32 × 10-1 cm s-1, respectively. The influence of pH on the oxidation of 4-AP was investigated and a pH value of 2.0 (using a phosphate buffer solution) was selected as the optimum pH. Under optimum conditions, the calibration was linear between 0.8 and 87 µM with a detection limit of 45 nM. Moreover, GPE/PtAM was applied to determine the concentrations of 4-AP in water samples with satisfactory results.

Modified glassy carbon electrode with Polydopamine-multiwalled carbon nanotubes for simultaneous electrochemical determination of biocompounds in biological fluids.

In this study, a simple modified glassy carbon electrode with Polydopamine-multiwalled carbon nanotubes (GCE/PDA-MWCNTs) is described for selective and sensitive simultaneous voltammetric determination of dopamine (DA), acetaminophen (AC), and xanthine (XN). A detailed investigation by field emission scanning electron microscopy, Fourier transform infrared spectroscopy and electrochemistry methods such as cyclic voltammetry (CV), electrochemical impedance spectroscopy, differential pulse voltammetry (DPV) and chronoamperometry are performed in order to elucidate the preparation process and properties of the GCE/ PDA-MWCNTs. The proposed modified electrode displays intense and indelible electrooxidation response for simultaneous determination of DA, AC, and XN to three well-separated peaks in the potential range from 0.0 to 0.8 V/Ag/AgCl using CV and DPV methods in phosphate buffer solution with pH 7.0. Under the optimum conditions, detection limits of 20, 30 and 50 nM were obtained for DA, AC and XN, respectively. Moreover, GCE/PDA-MWCNTs was successfully used for simultaneous determination of DA, AC and XN in real samples.

Poly (dopamine quinone-chromium (III) complex) microspheres as new modifier for simultaneous determination of phenolic compounds.

In this study, poly(dopamine-quinone chromium (III))-microspheres (PDQCM) were used for the modification of graphite paste electrode (GPE) for simultaneous voltammetric determination of 4-Amino Phenol (AP), Phenol (Ph) and 4-Nitro Phenol (NP). The PDQCM and the GPE modified with PDQCM were characterized by field emission scanning electron microscopy, Energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, electrochemical impedance spectroscopy and electrochemistry methods such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The proposed modified electrode exhibits high electrocatalytic activity toward electrooxidation of AP, Ph, and NP to three well-separated peaks in the potential range from 0.2 to 1.3V using CV and DPV methods in phosphate buffer solution with pH 2.0. Under the optimum conditions, detection limits of 0.5, 0.6 and 0.8µM were obtained for AP, Ph, and NP, respectively. Moreover, GPE/PDQCM was successfully used for simultaneous determination of AP, Ph, and NP in tap and river waters.

Poly(quercetin)-bismuth nanowires as a new modifier for simultaneous voltammetric determination of dihydroxybenzene isomers and nitrite.

Dihydroxybenzene isomers and nitrite, NO2 -, are present in the environment as highly toxic compounds and cause human cancer. In this study, for the first time poly(quercetin) (PQ) was synthesized from the reaction between quercetin (Q) and hydroquinone (HQ) as a linker. Bismuth nanowires (BNWs) were synthesized using a solvothermal technique and then the BNWs and PQ were used for preparation of a novel modified graphite paste electrode (GPE/PQ-BNWs) for simultaneous determination of dihydroxybenzene isomers; HQ, catechol (CC), resorcinol (RS) in the presence of NO2 -. The product was characterized using X-ray diffraction, field emission scanning electron microscopy and Fourier transform infrared spectroscopy. The electrochemical response characteristics of the modified GPE toward mix HQ, CC, RS and NO2 - were investigated by cyclic voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy. Under the optimum conditions, detection limits of 0.12, 0.2, 0.82 and 4.5 µM were obtained for HQ, CC, RS and NO2 -, respectively. Moreover, the GPE/PQ-BNWs were applied to determine HQ, CC, RS and NO2 - in water samples with satisfactory results.

Kinetic, isotherm and thermodynamic studies with linear and non-linear fitting for cadmium(II) removal by black carbon of pine cone.

In this study, black carbon from pine cone (BCPC) and acidic-modified BCPC (MBCPC) powder as a popular agricultural waste in the southeast of Iran were used for cadmium removal from aqueous solutions. The effect of various factors, such as surface chemistry and dosage of adsorbent, contact time, size of particles, initial concentration of cadmium, temperature, and pH of aqueous solutions, was investigated. The results show cadmium removal with usage of the mentioned adsorbents increased after acidic modification. It was noteworthy in this work that the removal percentage of pollutant was above 90% for suggested biosorbents. The obtained experimental data for optimum conditions were selected to model the adsorption behavior of the materials with usage of six isotherm equations via non-linear fitting method and the residual root mean square error estimation for each model. The adsorption of cadmium preferably fitted Khan and Langmuir-Freundlich isotherms for BCPC and MBCPC adsorbents, respectively. The kinetic studies via linear fitting method proved the second-order kinetic was the applicable model for the adsorption process. Thermodynamic studies show the adsorption process of cadmium onto BCPC and MBCPC was spontaneous and endothermic.

Adsorption behavior of Cr(VI) on modified natural zeolite by a new bolaform N,N,N,N',N',N'-hexamethyl-1,9-nonanediammonium dibromide reagent.

The demand for effective adsorbents is to increase in response to the widespread recognition of the deleterious health effects of Cr(VI)-oxyanions exposure through drinking water. In this study, Cr(VI)-oxyanions uptake from aqueous solutions by a new bolaform N,N,N,N',N',N'-hexamethyl-1,9-nonanediammonium dibromide reagent-modified natural zeolitic materials from Zahedan, Iran, was investigated using batch technique. Spectrophotometry method was used for Cr determination. The Cr(VI)-solution concentration varied between 2 and 104 mg L(-1). It was shown that the Cr(VI) uptake strongly depended on pH. The maximum removal of Cr(VI) occurred in acidic media at pH<1.5. The amounts of Cr(VI) adsorbed increased with increase in dose of both adsorbents and their contact time. Based on results an adsorption mechanism has been suggested. The adsorption data for modified zeolite using the amine was consistent with Langmuir isotherm equation and the equilibrium data was analyzed using the Langmuir isotherm.

Application of Ag2X (X=SO3(2-), Cr2O7(2-), C2O4(2-) and CO3(2-)) solid-phase reagents for indirect determination of cyanide in the industrial effluent using FIA-FAAS system.

Four solid-phase reagents have been tested for indirect determination of cyanide using flow injection analysis-flame atomic absorption spectrometry (FIA-FAAS). The method is based on insertion of aqueous cyanide solutions into an on-line Ag(2)X (where X are SO(3)(2-), Cr(2)O(7)(2-), C(2)O(4)(2-) and CO(3)(2-)) packed column (25%, m/m suspended on silica gel beads) and re-distilled water or sodium hydroxide are used as the carrier stream. The eluent containing the analyte as silver cyanide complexes, produced from reaction between Ag(2)X and cyanide, measured by flame atomic absorption spectrometry. The method is simple, fast and selective than other published FIA procedures. A relative standard deviation (R.S.D.) better than 1.12% was obtained in a repeatability study. The method was applied to the determination of cyanide in industrial electrolytic baths.

Specific extraction of chromium as tetrabutylammonium-chromate and spectrophotometric determination by diphenylcarbazide: speciation of chromium in effluent streams.

A very specific, selective, simple, and inexpensive procedure was developed for the speciation of CrVI and CrIII. This method is based on the quantitative extraction of chromate and CrIII (previously oxidized to CrVI) as a tetrabutylammonium-chromate ion-pair in methyl isobutyl ketone (MIBK), and then back extraction and preconcentration with an acidic diphenylcarbazide (DPC) solution. Back extraction was applied to achieve further preconcentration by a final factor of 20. The CrVI-DPC complex was determined in back-extract by a spectrophotometer at 548 nm. Under these extraction conditions, most of the probable concomitant cations and anions remained in the first inorganic phase. The calibration curve was linear up to 0.14 microg L(-1) of CrVI with a detection limit of 2.22 ng L(-1). The developed procedure was found to be suitable for the determination of the CrVI and CrIII species in various natural water samples with a relative standard deviation of better than 1.6%. The method was successfully applied to the speciation of chromium in spiked natural water samples, and also samples of effluent from a leather treatment plant.