An electrochemical sensor for p-aminophenol based on the mesoporous silica modified carbon paste electrode

A mesoporous silica was synthesised and used to modify the surface of carbon paste electrode (CPE). The electrochemical behaviours of p-aminophenol were investigated. Compared to the unmodified CPE, the mesoporous silica-modified CPE obviously lowers the oxidation potential of p-aminophenol, and remarkably increases its oxidation peak current. The effects of pH value, amount of mesoporous silica, accumulation potential and time were examined. As a result, a sensitive, rapid and convenient electroanalytical method was developed for p-aminophenol. The linear range is from 0.025?mg?L^?1 to 3?mg?L^?1, and the limit of detection is 0.01?mg?L^?1 after 2-min accumulation. Finally, the method was successfully used to determine p-aminophenol in water samples.     

Indirect detection of substituted phenols and cannabis based on the electrochemical adaptation of the Gibbs reaction

The voltammetric behaviour of 2,6-dichloro-p-aminophenol (PAP) in aqueous solution at an edge plane pyrolytic graphite electrode was explored and its sensitivity to additions of substituted phenols examined. Proof of concept is shown for the electrochemical adaptation of the Gibbs reaction, where reaction of the oxidised form of PAP with substituted phenols provides an indirect methodology for the analytical detection of these compounds. This indirect protocol provides an attractive alterative to the direct electrochemical oxidation of phenolic compounds, since the latter is plagued by electrode passivation, leading to low sensitivity. It is observed that phenol, 4-phenoxyphenol, methylphenol (para and meta), nitrophenol and most importantly, tetrahydrocannabinol, can be detected voltammetrically. Such a protocol is particularly attractive for roadside testing for cannabis in drug drivers.     

Amperometric sensor for hydrogen peroxide based on poly(aniline-co-p-aminophenol)

It was found that the poly(aniline-co-p-aminophenol) film can effectively catalyze the oxidation of hydrogen peroxide in a sodium citrate buffer solution with pH 5.0. Here, we applied the copolymer to the construction of an efficient electrochemical sensor to determine the concentration of hydrogen peroxide. The sensor exhibited an excellent electrocatalytic activity toward the oxidation of H₂O₂, and the interferences of ascorbic acid and phenol were completely avoided. Unlike the inherent instability of enzyme, the poly(aniline-co-p-aminophenol) film-based sensor showed an outstanding stability.     

Quenching Behavior of the Electrochemiluminescence of Ru(bpy)32+/TPrA System by Phenols on a Smartphone-Based Sensor

Phenolic compounds such as vanillic and p-coumaric acids are pollutants of major concern in the agro-industrial processing, thereby their effective detection in the industrial environment is essential to reduce exposure. Herein, we present the quenching effect of these compounds on the electrochemiluminescence (ECL) of the Ru(bpy)₃²⁺/TPrA (TPrA=tri-n-propylamine) system at a disposable screen-printed carbon electrode. Transient ECL profiles are obtained from multiple video frames following 1.2 V application by a smartphone-based ECL sensor. A wide range of detection was achieved using the sensor with limit of detection of 0.26 μM and 0.68 μM for vanillic and p-coumaric acids, respectively. The estimated quenching constants determined that the quenching efficiency of vanillic acid is at least two-fold that of p-coumaric acid under the current detection conditions. The present ECL quenching approach provided an effective method to detect phenolic compounds using a low-cost, portable smartphone-based ECL sensor.     

Simultaneous Kinetic Determination of Carbamate Pesticides after Derivatization withp-Aminophenol by Using Partial Least Squares

A method has been developed for the fast spectrophotometric determination of propoxur, carbaryl, and ethiofencarb in water samples using injection analysis in the stopped-flow mode. The method is based on the reaction betweenp-aminophenol and the phenolic compounds obtained from the pesticides, after a previous hydrolysis with 0.05MNaOH at room temperature for 15 min. The partial least-squares treatment of the spectrophotometry kinetic data provides a simultaneous determination of the three carbamate pesticides assayed with a relative accuracy error lower than 5% in complex mixtures also containing formetanate, which is only partially hydrolyzed under the experimental conditions and cannot be determined accurately by the above procedure.     

Electrochemical detection of phenolic compounds using composite film of multiwall carbon nanotube/surfactant/tyrosinase on a carbon paste electrode

A new tyrosinase-based biosensor was developed for detection of phenolic compounds using composite film of multiwall carbon nanotube (MWCNT)/dimethylditetradecylammonium bromide (DTDAB)/tyrosinase (Tyr) on a Nafion-incorporated carbon paste electrode. The biosensor showed a sensitive electrochemical response to the reduction of the oxidation products of different phenolic compounds (phenol, catechol, p-cresol, and p-chlorophenol) by dissolved O₂ in the presence of the immobilized enzyme. The effects of pH, operating potential, MWCNT concentration, and the DTDAB/Tyr ratio on electrochemical response were explored for optimum analytical performance. The biosensor exhibited a linear response range of 1.5–25.0, 2.0–15.0, 2.0–15.0, and 2.5–25.0 μM and sensitivity of 2,900, 3,100, 3,100, and 1,500 μA/mM for phenol, catechol, p-cresol, p-chlorophenol, respectively. In addition, the response of the enzyme electrode showed Michaelis–Menten behavior at concentrations of the phenolic compounds higher than 5.0 μM. The stability and the application of the biosensor were also evaluated.     

Development of an optical fibre reflectance sensor for p-aminophenol detection based on immobilised bis-8-hydroxyquinoline

2,2′-(1,4-Phenylenedivinylene)bis-8-hydroxyquinoline (PBHQ), a highly sensitive reagent used for the colorimetric determination of p-aminophenol (PAP), was successfully immobilised on XAD-7 and coupled with optical fibres to investigate a sensor-based approach for determining p-aminophenol. The solid-state sensor is based on the reaction of PAP with PBHQ in presence of an oxidant to produce an indophenol dye. The reflectance measurements were carried out at a wavelength of 647 nm since it yielded the largest divergence different in reflectance spectra before and after reaction with the analyte. The linear dynamic range of PAP was found within the concentration range of 0.1-2.18 mg l⁻¹ with its LOD of 0.02 mg l⁻¹. The sensor response from different probes (n = 7) gave a R.S.D. of 4.4% at 1.09 mg l⁻¹ PAP concentration. The response time of the optical one-shot sensor was 5 min for a stable solution. As this PAP sensor is irreversible, a fresh sensor has to be used for each measurement. All the experimental parameters were optimized for the determination of PAP. Using the optical sensing probe, PAP in pharmaceutical wastewater and paracetamol was determined. The effect of potential interferences such as inorganic and organic compounds was also evaluated. Potential on-site determination of PAP with such sensors can indirectly aid detection of organo-phosphorus nerve agents and pesticides in the field by inhibition of acetylcholine esterase-catalyzed hydrolysis of p-aminophenyl acetate to p-aminophenol.     

Nafion-graphene composite film modified glassy carbon electrode for voltammetric determination of p-aminophenol

A Nafion-graphene (Nafion-GR) nanocomposite film modified glassy carbon electrode was fabricated by a simple drop-casting method, and used in the electrochemical detection of p-aminophenol (4-AP). Owing to the large surface area, good conductivity of GR and good affinity of Nafion, the sensor exhibited excellent electrocatalytic activity for the oxidation of 4-AP. The electrochemical behaviors of 4-AP on Nafion/GR film modified glassy carbon electrodes were investigated by cyclic voltammetry and differential pulse voltammetry. A calibration curve is constructed in the same matrix, urine, as the unknown samples to be analyzed. The Nafion-GR film modified electrode was linearly dependent on the 4-AP concentration and the linear analytical curve was obtained in the ranges of 0.5–200 μM with differential pulse voltammetry (DPV) and the detection limit was 0.051 μM. The Nafion-graphene nanocomposite modified electrode exhibited good reusability than pure graphene modified GCE. This procedure can be used for the determination of p-aminophenol in the presence of its degradation products and paracetamol. Finally, the proposed method was successfully used to determine p-aminophenol in local tap water samples in urine samples and pharmaceutical preparations.     

Composite electrodes consisting Pt nano-particles and poly (aminophenols) film on pre-treated aluminum substrate as electrocatalysts for methanol oxidation

Electrochemically platinum plated aluminum (Al/Pt) was used as an electrode substrate for the electropolymerization of aminophenols and fabrication of composite electrodes based on platinum nano-particles. The poly(o-aminophenol) (PoAP), poly(m-aminophenol) (PmAP), and poly(p-aminophenol) (PpAP) were synthesized on the Al/Pt electrode, and further modification was performed by deposition of platinum nano-particles onto polymer matrixes. The electrochemical and morphological characteristic of the composed electrodes were carried out by cyclic voltammetry and scanning electron microscopy, respectively. The electrocatalytic oxidation of methanol on the composite electrodes was studied by cyclic voltammetry in 0.1 M sulfuric acid as supporting electrolyte. It was found that the Al/Pt/PoAP electrode incorporated Pt nano-particles (Al/Pt/PoAP/Pt) exhibits a higher electrocatalytic activity for the oxidation of methanol than the Al/Pt/PmAP/Pt and Al/Pt/PpAP/Pt electrodes. On the other hand, a higher catalytic current for methanol oxidation was found on the Al/Pt/PoAP/Pt electrode in comparison to bulk Pt and Al–Pt (Al with 0.2 mg cm⁻² of Pt particles) electrodes. The effects of various parameters such as thickness of the polymer film, concentration of the monomer, Pt loading method and the Pt amounts, concentration of the methanol, and the medium temperature were studied on the electrooxidation of methanol. The long-term stability of the modified electrode has also been investigated.     

Effect of monomer functional groups on the composition of some three component random phenolic copolymers

Some three-component random phenolic copolymers were prepared from three typical phenolic monomers; for example, p-chlorophenol, p-aminophenol, and p-cresol. Several samples of the copolymer were prepared by changing the feed composition and the composition of the copolymers was established by estimating ? NH₂ and ? OH groups by electrometric titration techniques in nonaqueous media. Halogen was estimated by Volhard's method. The average degree of polymerization (DP) of the copolymers was calculated from the features of the electrometric titration curves, and the effects of monomer functional groups on the composition of the copolymers were interpreted in terms of the electron-donating and electron-attracting nature of the substituents present in the monomers.     

p-aminophenyl phosphate: an improved substrate for electrochemical enzyme immnoassay

An alternative substrate is described for enzyme immunosaasay with electrochemical detection. Alkaline phosphatase (EC.3.1.3.1) activity is determined by using p-aminophenyl phosphate as the enzyme substrate. Enzyme-generated p-aminophenol is detected amperometrically at a glassy carbon electrody by liquid chromatography with electrochemical detection. The oxidation potential obtained for the detectionof p-aminophenol is lower than that for phenol, the previously used substrate product. The detection limit for p-aminophenol is 0.20pmol. A detection limit of 30 pg ml^-1 for digoxin and a 5-min incubationtime for the enzyme reaction were obtained with the new system.     

A Nonenzymatic Glucose Sensor Using Nanoporous Platinum Electrodes Prepared by Electrochemical Alloying/Dealloying in a Water‐Insensitive Zinc Chloride‐1‐Ethyl‐3‐Methylimidazolium Chloride Ionic Liquid

We report here a nonenzymatic sensor by using a nanoporous platinum electrode to detect glucose directly. The electrode was fabricated by electrochemical deposition and dissolution of PtZn alloy in zinc chloride‐1‐ethyl‐3‐methylimidazolium chloride (ZnCl₂‐EMIC) ionic liquid. Both SEM and electrochemical studies showed the evidences for the nanoporous characteristics of the as‐prepared Pt electrodes. Amperometric measurements allow observation of the electrochemical oxidation of glucose at 0.4 V (vs. Ag/AgCl) in pH 7.4 phosphate buffer solution. The sensor also demonstrates significant reproducibility in glucose detection; the higher the roughness factor of the Pt electrode, the lower the detection limit of glucose. The interfering species such as ascorbic acid and p‐acetamidophenol can be avoided by using a Pt electrode with a high roughness factor of 151. Overall, the nanoporous Pt electrode is promising for enzymeless detection of glucose at physiological condition.     

Poly(dimethylsiloxane) microchip capillary electrophoresis with electrochemical detection for rapid measurement of acetaminophen and its hydrolysate

Poly(dimethylsiloxane) microchip capillary electrophoresis with amperometric detection has been used for rapid separation and determination of acetaminophen and its hydrolysate, i.e. p-aminophenol. A Pt ultramicroelectrode with a diameter of 10 m positioned at the outlet of the separation channel was used as a working electrode for amperometric detection. Factors influencing separation and detection were investigated and optimized. Results show that acetaminophen and p-aminophenol can be well separated within 35 s with RSD<1% for migration time and <7% for detection current for both analytes. Detection limits for both analytes are estimated to be 5.0 mol L^–1 (approximately 0.1 fmol) at S/N=3. This method has been successfully applied to the detection of traces of p-aminophenol in paracetamol tablets.     

Arthrobacter sp. JS443‐Based Whole Cell Amperometric Biosensor for p‐Nitrophenol

An amperometric microbial biosensor for highly sensitive and selective determination of p‐nitrophenol (PNP) is reported. The biosensor consisted of PNP‐degrader Arthrobacter sp. JS443 immobilized by entrapment in Nafion polymer deposited on the top of the carbon paste electrode transducer. The biosensor was based on the measurement of the oxidation current of the intermediates 4‐nitrocatechol and 1,2,4‐benzenetriol formed by the highly selective oxidation of PNP by Arthrobacter sp. The sensor signal and response time were optimized with applied potential of +0.4 V (vs. Ag/AgCl reference electrode) and 0.03 mg of cells and operating in pH 7.5, 50 mM citrate‐phosphate buffer at room temperature. When operated at optimized conditions, the Arthrobacter sp.‐based biosensor measured as low as 5 nM (0.7 ppb) of PNP. The biosensor demonstrated excellent selectivity with no interference from phenolic compounds such as 2‐nitrophenol, phenol and 3‐chlorophenol but was interfered by 3‐nitrophenol and 3‐methyl‐4‐nitrophenol. It had good precision and intra‐ and inter‐day reproducibility, accuracy and was stable up to 3 days when stored in buffer at 4 °C. When applied for measurement in water from Lake Elsinore, CA, the results obtained were in excellent agreement with the amounts determined spectrophotometrically.     

Introducing an amine group to calix[5]arene: comparison of several methods

Abstract

Chemists often use an amine group as an intermediate in syntheses of imines, amides and ureas; however, in the case of syntheses of p-aminophenol type compounds, several problems might occur. In this article, we prepared p-aminocalix[5]arene-pentaol by reduction of both nitro and azo derivatives, and compared four methods of the amine preparation, focusing mainly on its gramme scale and time-consuming issues.     

Simultaneous Determination of Epinephrine and Dopamine by Using Candida tropicalis Yeast Cells Immobilized in a Carbon Paste Electrode Modified with Single Wall Carbon Nanotube

A new electrochemical microbial biosensor system based on Candida tropicalis was developed for the fast detecting of dopamine and epinephrine. Candida tropicalis was immobilized in a carbon paste electrode (CPE) with single wall carbon nanotube (SWCNT). Immobilized cells were used as a origin of the polyphenol oxidase (PPO) to develop voltammetric epinephrine and dopamine biosensor. Voltammetric determination of phenolic compounds such as epinephrine and dopamine a simple technique which is available. Direct oxidation of phenols can be used, but the oxidation potentials of this compounds are similar and they can not be detected distinctively. Another possibility is the use of biosensors based on the polyphenol oxidase (tyrosinase) enzyme that oxidizes the phenolic compounds into their related quinones. By this way, phenolic compounds are epinephrine and dopamine which were used in this study as well detected at different potentials. In this study differential pulse voltammetry and amperometry techniques were used for the determination of dopamine and epinephrine. The effect of varying the amounts of SWCNT and the response of microorganism to epinephrine was investigated to find the optimum composition of the sensor. The effects of pH and temperature were also examined. Increases in biosensor responses obtained by amperometric measurements were linearly related to dopamine concentrations between 0.025 and 0.25 mM and epinephrine concentrations between 0.01 and 0.1 mM. Limits of detection of the biosensor for dopamine and epinephrine were calculated to be 0.008 and 0.0023 mM, respectively. Finally, proposed system was applied to epinephrine and dopamine analysis in pharmaceutical drugs and synthetic serum and the results were compared with LC MS MS method.     

Rapid electrochemical assay for theophylline in whole blood based on the inhibition of bovine liver alkaline phosphatase

A disposable electrochemical test strip for determining clinically relevant concentrations of theophylline (0–300 μM) in whole blood is described, based on the generation of p-aminophenol from p-aminophenyl phosphate by the action of bovine liver alkaline phosphatase. Theophylline is an uncompetitive inhibitor of alkaline phosphatase and thus inhibits this process. The test strip consists of a screen-printed, carbon-based electrode system containing the enzyme and substrate in separate layers. Application of a 20-μl blood sample to the strip initiates the enzymic reaction, which will proceed to an extent that is inversely dependent on the amount of theophylline in the sample. After a 2-min incubation, the p-aminophenol generated is quantified by its electrochemical oxidation at + 150 mV (vs. Ag/AgCl) on the underlying carbon electrode. Caffeine and theobromine (0–1 mM), phenylalanine (< mM) and endogenous alkaline phosphatase (<2 U ml ^?1) do not interfere.     

Poly(2,2′-(1,4-phenylenedivinylene) Bis-8-hydroxyquinaldine) Modified Glassy Carbon Electrode for the Simultaneous Determination of Paracetamol and p-Aminophenol

A novel assay is reported for the simultaneous determination of paracetamol and p-aminophenol using a poly(2,2′-(1,4-phenylenedivinylene)bis-8-hydroxyquinaldine) modified glassy carbon electrode. Poly(2,2′-(1,4-phenylenedivinylene)bis-8-hydroxyquinoline) modified electrodes were prepared by electrochemical polymerization. The electrode surface was characterized by scanning electron microscopy. The electrochemical behavior of the modified electrode was investigated by cyclic voltammetry, square wave voltammetry, and electrochemical impedance spectroscopy. The anodic peak potentials for paracetamol and p-aminophenol were at 580 and 337 millivolts, respectively, with a separation of 243 millivolts, adequate for their simultaneous determination. The results showed that the linear dynamic ranges for paracetamol and p-aminophenol were 0.5–200 micromolar and 3–150 micromolars, whereas the limits of detection were 0.075 and 0.45 micromolar, respectively. The novel poly(2,2′-(1,4-phenylenedivinylene)bis-8-hydroxyquinaldine) modified electrode provided excellent selectivity, sensitivity, and stability and was employed for the determination of paracetamol and p-aminophenol in pharmaceutical products and urine.     

Electro-oxidation of o-aminophenol studied by cyclic voltammetry and surface enhanced Raman scattering (SERS)

Cyclic voltammetry and surface enhanced Raman scattering (SERS) spectra were used over a wide pH range to examine the products of o-aminophenol oxidation on a roughened silver electrode. The results of the study indicated that at least two oxidation products are formed at the stationary potential of the electrode. The major product in alkaline and neutral media was identified as 2,2′-dihydroxyazobenzene, a linear dimer formed by N---N coupling of o-aminophenol cation radicals. In acidic solutions the cyclic dimer 3-aminophenoxazone formed by C---N coupling of o-aminophenol cation radicals dominates on the silver electrode.     

Simultaneous detection of ascorbate and uric acid using a selectively catalytic surface

The direct and selective detection of ascorbate at conventional carbon or metal electrodes is difficult due to its large overpotential and fouling by oxidation products. Electrode modification by electrochemical reduction of diazonium salts of different aryl derivatives is useful for catalytic, analytical and biotechnological applications. A monolayer of o-aminophenol (o-AP) was grafted on a glassy carbon electrode (GCE) via the electrochemical reduction of its in situ prepared diazonium salts in aqueous solution. The o-aminophenol confined surface was characterized by cyclic voltammetry. The grafted film demonstrated an excellent electrocatalytic activity towards the oxidation of ascorbate in phosphate buffer of pH 7.0 shifting the overpotential from +462 to +263 mV versus Ag/AgCl. Cyclic voltammetry and d.c. amperometric measurements were carried out for the quantitative determination of ascorbate and uric acid. The catalytic oxidation peak current was linearly dependent on the ascorbate concentration and a linear calibration curve was obtained using d.c. amperometry in the range of 2-20 μM of ascorbate with a correlation coefficient 0.9998, and limit of detection 0.3 μM. The effect of H₂O₂ on the electrocatalytic oxidation of ascorbate at o-aminophenol modified GC electrode has been studied, the half-life time and rate constant was estimated as 270 s, and 2.57 × 10⁻³ s⁻¹, respectively. The catalytically selective electrode was applied to the simultaneous detection of ascorbate and uric acid, and used for their determination in real urine samples. This o-AP/GCE showed high stability with time, and was used as a simple and precise amperometric sensor for the selective determination of ascorbate.