Flow-Injection Biamperometry of Phenol

ABSTRACT

A simple and rapid method determination of phenol is described, using a bromination reaction and biamperometric detection. The method is based on measurements of the intensity of current passing through two identical inert electrodes giving the concentration of phenol in samples. The sample is injected into a stream of carrier and merged with a stream of acidic bromine solution which brominates phenol in the reaction coil. A linear relationship between peak height and phenol concentration is observed in the range of 0.05 to 8 μg ml^?1 of phenol. The relative standard deviation was 2.8% for analysis of 5μg ml^?1 phenol and the sampling rate was 70 h^?1     

Electrocatalytic Phenol Oxidation on Mixed Pt‐RuO2 Nanoparticle Modified Electrode

Abstract

Nanoscale Pt/RuO₂ colloid with carbon paste support was synthesized and used to prepare a modified electrode for phenol detection. The results showed that the Pt/RuO₂ catalyst has high activity for electrooxidation of phenol with reduced intermediate polymerization due to its significantly low potential for phenol oxidation. The detection limit was as low as 10^?9 mol L^?1 for the polishable Pt/RuO₂/C paste electrode with good reproducibility.     

Spectrophotometic Determination Of Tin In Steels With2-(5-Nltro-2-Pyridylazo)-5-[N-n-Propyl-N-(3-Sulfopropyl)Amino]phenol

ABSTRACT

A highly sensitive azo dye, 2-(5-nitro-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]phenol (Nitro-PAPS), is used as a colorimetric reagent for the determination of tin(IV) content. Nitro-PAPS reacts with tin(IV) to form a water-soluble complex in 1.0 M acetic acid. Full color development is attained within 5 minutes, and maintains constant absorbance for at least 24 hours. The apparent molar absorptivity is 7.7 x 10⁴ dm³ mol^?1 cm^?1 at a maximum wavelength of 580 ran. Beer's law is obeyed for tin(IV) in the range of 0-1.2 μg ml^?1. The proposed method is successfully applied to the determination of trace amounts of tin in steels.     

Critical Solution Temperatures for Two Phase Solvent Systems with Halide Salts,Carboxylic Acids,Surfactants, and Polynuclear Aromatic Compounds

Upper critical solution temperatures (UCST) of water‐phenol systems are reported with 0.1 mol kg^?1 halide salts, carboxylic acids, 1.0% PEG 200 in water, and 0.01 mol kg^?1 surfactants and polynuclear aromatic compounds namely benzene, naphthalene, anthracene, chrysene; and benzene derivatives solutions in phenol. The valence electrons and shell numbers, bascity, ‐CH₃ and ‐CH₂‐, hydrophilic, hydrophobic and π conjugated electrons of respective additives have been noted to affect the UCST values and mutual solubilities of the water and phenol. The surfactants decrease the UCST values with higher mutual solubilities due to effective hydrophilic as well as hydrophobic interactions with aqueous and organic phases, respectively. The stronger structure breaking action of the 3(‐OH) of the glycerol outweighs than those of the 3(‐COO^?) and 1(‐OH) of the citric acid and the urea does produce almost equal UCST values as compared to glycerol. A decrease in the UCST values is noted with number of conjugated π electrons of the benzene, naphthalene, anthracene, and chrysene. In general, the dTc/dx₂ values of salts for 0.20–0.16 mole fractions of phenol are found positive while for 0.055–0.052 mole fractions, the negative.     

Kinetics of oxidation of phenylhydrazine by a μ-oxo diiron(III,III) complex in acidic aqueous media

Phenylhydrazine (R) quantitatively reduces [Fe₂(μ-O)(phen)₄(H₂O)₂]⁴⁺ (1) (phen?=?1,10-phenanthroline) and its conjugate base [Fe₂(μ-O)(phen)₄(H₂O)(OH)]³⁺ (2) to [Fe(phen)₃]²⁺ in presence of excess 1,10-phenanthroline in the pH range 4.12–5.55. Oxidation products of phenylhydrazine are dinitrogen and phenol. The reaction proceeds through two parallel paths: 1?+?R?→?products (k ₁), 2?+?R?→?products (k ₂); neither RH⁺ nor the doubly deprotonated conjugate base of the oxidant, [Fe₂(μ-O)(phen)₄(OH)₂]²⁺ (3) is kinetically reactive though both are present in the reaction media. At 25.0°C, I?=?1.0?M (NaNO₃), the rate constants are k ₁?=?425?±?10?M^?1?s^?1 and k ₂?=?103?±?5?M^?1?s^?1. An inner-sphere, one-electron, rate-limiting step is proposed.     

Determination of Phenolic Compounds Based on Co‐Immobilization of Methylene Blue and HRP on Multi‐Wall Carbon Nanotubes

This work evaluated an amperometric biosensor based on multi‐wall carbon nanotubes (MWCNT), chemically modified with methylene blue (Met) and horseradish peroxidase (HRP), for detection of phenolic compounds. The dependences of the biosensor response due to the enzyme immobilization procedure, HRP amounts, pH and working potential were investigated. The amperometric response for catechol using the proposed biosensor showed a very wide linear response range (1 to 150 μmol L^?1), good sensitivity (50 nA cm^?2 μmol^?1 L), excellent operational stability (after 300 determinations the response remained at 97%) and very good storage stability (lifetime>3 months). Based on all these characteristics, it is possible to affirm that the material is promising for phenol detection due to its good electrochemical response and enzyme stabilization. The biosensor response for various phenolic compounds was investigated.     

Study of Transition States of Melamine for Micromixing with Wax Emulsion+4‐Nonyl Phenol Ethoxylate,Estimated with SEM Technique

Densities (ρ/10³kg m^?3), apparent molar volume (V₂/10^?6m³mol^?1), and viscosities (η/0.1 kg m^?1s^?1) for 5.0 to 60.0 millimol kg^?1 (m mol kg^?1) 1,3,5 triazine (melamine) at interval of 5.0 m mol kg^?1 were determined. The data were regressed and extrapolated to infinite dilution (m→0) and referred to as limiting apparent molal volume (V¯₂ ⁰) and intrinsic viscosity (B) and used to calculate free energy of activation (Δµ₂ ^0*/KJ mol^?1). Such functions illustrate feasibility of micromixing of melamine with paraffin wax emulsifier+4‐nonyl phenol ethoxylate, a nonionic surfactant in aqueous solution. The Δµ₂ ^0* decides micromixing of melamine stabilized by poly(acrylic acid) of 4500 g mol^?1 molecular weight, known as superabsorber for water. Paraffin wax emulsion was stabilized by a nonyl phenol ethoxylate and wax particles observed to adhere to melamine surface due to interactions between poly(acrylic acid) dispersant and ethoxylate group of surfactant, resulting in sedimentation of mixed particles. Thus V¯₂ ⁰, B, and Δµ₂ ^0* values conclude to ‐NH₂ group interactions for micromixing and scanning electron micrograph (SEM) elucidates microstructure and uniformity of micromixing.     

A CNDO/2 study of the OH torsion in phenol and its hydrogen bonded complex with pyridine

The CNDO/2 molecular orbital method has been applied to the study of the OH torsion, in phenol and phenol—pyridine hydrogen bonded complex. The calculated torsional barrier (13.58 kJ mol^?1) and force constant (5.4 × 10^?20 J rad^?2) of phenol agree well with the experimental quantities. The calculated force constant of the corresponding vibration in phenol—pyridine is increased sixfold, reproducing closely the rise in the torsional frequency observed when phenol is complexed to strong acceptors. It is shown that according to CNDO theory, most of the increase can be attributed to the influence of the intermolecular force field and not to a major change in the torsional force constant.     

A Prospect for the Analysis of Species Acting as Enzyme Inhibitors as Illustrated by Heavy Metal Inhibition

Abstract

A flow system incorporating an amperometric glucose oxidase enzyme electrode has been used to study the inhibitory effects of 16 metal cations on glucose oxidase. Only copper(II), mercury(II) and silver(I) caused any significant inhibition. the enzyme electrode could be reactivated by EDTA, the reactivation being most effective for copper(II) and least so for silver(I). Other complexing agents were tried for reactivation but proved to be unsatisfactory.

The ability to reactivate the enzyme on the electrode following copper(II) inhibition, and the linear response of the system to the level of this inhibitor according to I/A = -9.49 × 10^?7 log([Cu]/M) + 4.84 × 10^?8; r = 0.994 between 2.5 × 10^?4M and 5 × 10^?3M [Cu]²⁺ indicates a prospect for the use of a flow system for determining enzyme inhibitors in samples.     

Amplified Electrochemical Response of Phenol by Oxygenation of Tyrosinase Coupling with Electrochemical‐chemical‐chemical Redox Cycle

In this work, an novel electrochemical‐chemical‐chemical (ECC) redox cycle was designed in an enzyme‐based sensor for acquiring additional signal amplification. The tyrosinase (Tyr) was entrapped in a sulfonated polyaniline?chitosan (SPAN?CS) composite which was used as a redox capacitor on a glass carbon electrode. Firstly, the substrate, phenol was catalyzed to catechol and further catalyzed to o‐benzoquinone by Tyr. Next, in the presence of Ru(NH₃)₆Cl₂, the reduced state of SPAN(SPAN_red) was reacted with o‐benzoquinone to form it's oxidized state (SPAN_ox) and catechol, then SPAN_ox was reduced back to SPAN_red by Ru(II) in the solution. Finally, the amplified anodic current of catechol was obtained on electrode through above ECC redox cycle system. In addition, the ECC redox cycling led to a high signal‐to‐background ratio. The voltammetric response showed excellent analytical performance to phenol over two linear range of 3.5 to 200.0 nmol L^?1 and 200.0 to 2000.0 nmol L^?1 with a high sensitivity of 2204 μA mM^?1. The detection limit was obtained to be 0.8 nmol L^?1 (S/N=3). Furthermore, the proposed approach exhibited good repeatability, stability and specificity, and could offer practicality in the detection of phenol in tap water.     

Analysis of Sub-Microgram Levels of Palladium (II) in Environmental Samples by Selective Extraction and Spectrophotometric Determination with N-p-Methoxyphenyl-2-Furylacrylohydroxamic Acid and 5-(Diethylamino)-2-(2-Pyridylazo) Phenol

Abstract

Nine new hydroxamic acids in conjunction with four pyridylazo reagents were explored for extractive separation and spectrophotometric determination of palladium in environmental samples. It was found that maximum sensitivity and selectivity was achieved by employing N-p-methoxyphenyl-2-furylacrylohydroxamic acid (MFHA) and 5-(diethylamino)-2-(2-pyridylazo) phenol (DEPAP). Palladium was first selectively extracted with MFHA in isoamyl alcohol at pH 2.7-3.5 and the extract was equilibrated with a mixture of 5 M HCl and 10^{? 3} M solution of DEPAP in ethanol. The resulting intensely green ternary complex was measured at 560 nm (σ 5.1 × 10⁴ l mole^?1 cm^?1). The extraction system is suitable for enrichment of palladium over 15 times without loss in recovery and enables determination of palladium at levels as low as 10^?4 ppm (0.1 ppb). The method tolerates the presence of a large number of diverse ions normally associated with palladium, including platinum metals, and was employed for the determination of palladium in standard catalysts, biological materials, and freshwaters.     

Electro-catalytic effect of Al2O3 supported onto activated carbon in oxidizing phenol at graphite electrode

In this work, the electro-catalytic oxidation of phenol was studied using the aluminum oxide supported onto activated carbon (Al₂O₃/AC). The later was successfully prepared by impregnating aluminum particles in the activated carbon (AC) using heat treatment. Al₂O₃/AC was characterized by X-ray diffraction (XRD) and infrared spectroscopy (IR). The electro-catalytic performance of the Al₂O₃/AC for phenol oxidation was studied using cyclic voltammetry (CV), chronoamperometry, linear sweep voltammetry polarization, electrochemical impedance spectroscopy and differential pulse voltammetry (DPV) in 0.1 mol L^?1 Na₂SO₄. It has been shown that the proposed catalyst exhibits remarkably an electro-catalytic performance toward phenol oxidation. Moreover, the oxidation peak currents are linearly dependent on the concentration of phenol in the wide ranges from 1.0 × 10^?3 mol L^?1 to 1.0 × 10^?4 mol L^?1 and 8.0 × 10^?5 mol L^?1 to 1.0 × 10^?6 mol L^?1 with a detection limit of 1.51 × 10^?7 mol L^?1 (signal (S) to noise (N) ratio, S/N = 3) and response time of 3 min. The possible interferences were evaluated in 1.0 × 10^?5 mol L^?1 of phenol. The proposed catalyst also indicated suitable repeatability and stability. Moreover, the proposed Al₂O₃/AC–CPE has been successfully applied for the phenol analysis in natural waters and olive oil samples with good recoveries.     

Amperometric Biosensor for the Determination of Phenols Using a Crude Extract of Sweet Potato (Ipomoea Batatas (L.) Lam.)

Abstract

An amperometric biosensor for the determination of phenols is proposed using a crude extract of sweet potato (Ipomoea batatas (L.) Lam.) as an enzymatic source of polyphenol oxidase (PPO; tyrosinase; catechol oxidase; EC 1.14.18.1). The biosensor is constructed by the immobilization of sweet potato crude extract with glutaraldehyde and bovine serum albumin onto an oxygen membrane. This biosensor provides a linear response for catechol, pyrogallol, phenol and p-cresol in the concentration ranges of 2.0×10^?5-4.3×10^?4mol L^?1, 2.0×10^?5-4.3×10^?4 mol L^?1, 2.0×10^?5-4.5×10^?4 mol L^?1 and 2.0×10^?5-4.5×10^?4mol L^?1, respectively. The response time was about 3–5 min for the useful response range, and the lifetime of this electrode was excellent for fifteen days (over 220 determinations for each enzymatic membrane). Application of this biosensor for the determination of phenols in industrial wastewaters is presented.     

Microbiosensor for Salicylate Based on Modified Carbon Fibre

ABSTRACT

A microbiosensor is proposed for a quick and easy amperometric determination of salicylate. The methodology involves the use of the enzyme salicylate hydroxylase (SH) to convert salicylate to catechol, which is then oxidised at the carbon fibre electrode. The covalent immobilisation of the enzyme onto a carbon fibre electrode via carbodiimide results in an amperometric biosensor with high sensitivity, low detection limit and good stability. The response of the biosensor is linearly proportional to the salicylate concentration between 1.0 10^?7 and 2.0 10^?6 mol L^?1, at an applied potential of 300 mV vs SCE, with a response time of 3.5 s and a detection limit of 3.3 10^?8 mol L^?1. The relative standard deviation for the determination was 4.1% for n=10. The biosensor was applied to determine salicylate in urine and pharmaceutical samples and compared to the reference method with a good correlation.     

Chitosan‐Based Glucose Oxidase Electrodes Enhanced by Silver Nanoparticles

Silver nanoparticles enhanced glucose oxidase electrodes were prepared on the basis of chitosan matrix. The enzyme electrodes exhibited high sensitivity and excellent response performance to glucose with a linear range from 1×10^?6 to 8×10^?3 mol · L^?1. And the time reaching the steady‐state amperometric response was less than 5 seconds. The inhibition percentage of this enzyme electrode against copper ions concentration was linear ranging from 1.2×10^?6 to 5×10^?5 mol · L^?1. These properties of enzyme electrodes are probably due to the excellent electron transfer of silver nanoparticles and the orientation of glucose oxidase molecule.     

Influence in kinetic studies by competitive photocurrent methods of a post-competition link between parallel reactions chains: Part II. OH radical addition to phenol and aniline

The rate constants for the homogeneous reaction of OH radicals of O^? ions with phenol and aniline have been determined by a photoelectrochemical method involving studies of the suppressive effect of mixtures of aniline and of phenol with methanol on the nitrous oxide photocurrent at a DME. Fairly good agreement with absolute rate constants obtained by conventional radiation chemical methods is obtained if use is made of the theory developed in Part I of this paper which takes account of the possibility of interaction between the photocurrent reaction chains following competition between the two organic solutes for OH radicals. The present work points to a value of 1.75±0.6 10¹⁰M^?1 s^?1 for the capture of OH by phenol at pH 9.5. The reaction product, the cyclohexadienyl radical Φ (OH)₂, is able to extract H atoms from methanol with a rate constant of the order of 10⁷M^?1 s^?1, this reaction tending to lessen the suppressive effect of a phenol + methanol mixture on the nitrous oxide photocurrent. Similar complications are observed at higher pH, and also when using aniline + methanol mixtures.     

Determination of Fluoride,Cyanide, and Thiocyanate Using Horseradish Peroxidase Immobilized on Modified Silica Gel

Abstract

Silica gels modified with different functional groups (amino, epoxy, cycloepoxy, isocyanate, and thiocyanate) were used for the covalent immobilization of horseradish peroxidase (HRP). The catalytic activity and stability of the obtained enzyme preparations were studied using the reaction of o‐dianisidine oxidation with hydrogen peroxide as an indicator. The covalent immobilization of horseradish peroxidase using silica gel modified with thiocyanate groups provided not only the improvement of the enzyme stability, but also the development of the sensitive, rapid, and simple procedures for the determination of fluoride, cyanide, and thiocyanate. Enzymatic determination of inorganic anions is based on their inhibitory effect on the enzyme as the ligands capable to form stable complexes with Fe(III)‐HRP cofactor. The proposed procedures were applied for the determination of F^? in mineral and drinking waters; CN^? and SCN^?—in biological fluids (blood and saliva).     

Development and Application of an Immobilized Enzyme Electrode for the Determination of Sulfite in Foods and Feeds

Abstract

An enzyme electrode was developed using the enzyme sulfite oxidase (EC 1.8.3.1) immobilized onto pig intestine. All experimental parameters such as pH, temperature, buffer constituent concentration, etc., were thoroughly investigated and optimized when appropriate. Hydrogen peroxide was monitored amperometrically. The response to sulfite concentration was linear in the range of 5.2 × 10^?6 to 1.0×10^?3M. The proposed method was found to have a correlation coefficient of 0.952 when evaluated versus the standard titration method.     

Syntheses and crystal structures of two Schiff-base copper(II) complexes with antibacterial activities

Two structurally similar trinuclear complexes, [Cu(Cu(μ-Cl)₂L1)₂] (1) and [Cu(Cu(μ-Cl)₂L2)₂] (2) (HL1 = 4-chloro-2-[(2-morpholin-4-ylethylimino)methyl]phenol, HL2 = 1-[(2-piperidin-1ylethylimino)methyl]naphthalen-2-ol), have been synthesized and structurally characterized. Both complexes are bridged trinuclear compounds. The central Cu in each complex is in an octahedral environment with two phenolate and four bridging chlorides. The symmetry-related terminal Cu in each complex is square pyramidal with one phenolate oxygen, one imine nitrogen and one amine nitrogen of the Schiff-base ligand, one Cl^? in the basal plane, and one bridging Cl^? in the apical position. The complexes and Schiff bases were tested in vitro for their antibacterial activities.     

Flow Injection Chemiluminescence Determination of Phenol in Neutral Medium

A new flow injection chemiluminescence method for the determination of phenol was proposed, based upon the chemiluminescence reaction of phenol, N-bromosuccinimide, and hydrogen peroxide in neutral aqueous medium in the presence of cetyltrimethylammonium bromide surfactant micelles. The chemiluminescence signal was proportional to the concentration of phenol in the range of 1.0 × 10^?7?8.0 × 10^?6 g/mL with a detection limit of 3 × 10^?8 g/mL. The relative standard deviation for 1.0 × 10^?6 g/mL phenol solution was 2.0% (n = 11). The proposed method was successfully applied to the determination of phenol in phenol ear drops. A possible CL reaction mechanism was also discussed briefly.