A Cobalt Film Electrode for Nitrite Determination in Natural Water

In this study a cobalt film electrodeposited on a copper disk (Ø=3.1 mm) was tested as electrode to measure nitrite ions in raw water. This electrode was able to determine the nitrite ions concentration in nondeaerated synthetic media and in natural water. The electrode reached a detection limit of 0.2 μmol L^?1 and has a linear concentration range of 0.4 to 2 μmol L^?1 NO₂^?. The influence of several ions such as NO₃^?, Cl^?, SO₄^2?, Mg²⁺, HCO₃^? and NH₄⁺ was also tested. The electrode was used to determine the concentration of nitrite ions in a real sample.     

Electrochemical Behavior and Voltammetric Determination of Chloramphenicol and Doxycycline Using a Glassy Carbon Electrode Modified with Single-walled Carbon Nanohorns

We report a method for the direct and quantitative determination of chloramphenicol (CAP) and doxycycline (DOX) using a glassy carbon electrode (GCE) modified with carboxylic-group-functionalized single-walled carbon nanohorns. The modified electrode exhibits high electrocatalytic activity towards the reduction of CAP and the oxidation of DOX. It shows a linear response to CAP between 0.1 μM and 100 μM and to DOX between 0.5 μM and 100 μM. The detection limits for CAP and DOX are 0.1 μM and 0.5 μM, respectively. The modified GCE displays good sensitivity, making it suitable for the determination of CAP and DOX in real samples.     

A Highly Sensitive Method for Determination of Monobutyltin in Aqueous Media by Stripping Voltammetry at a Renewable Silver Amalgam Annular Band Electrode

An adsorptive stripping voltammetric (AdSV) procedure for the determination of monobutyltin in aqueous media at a silver liquid amalgam film‐modified silver solid amalgam annular band electrode (AgLAF? AgSAE) is described. Determination of monobutyltin proceeds in two steps. At the beginning monobutyltin ions (BuSn³⁺) are accumulated from 0.1 M NH₄NO₃ and 10 % ethanol solution at a potential of ?0.2 V, than the BuSn⁰ film is preconcentrated at the working electrode surface at a potential of ?0.7 V. After this step the DP AdSV voltammogram is recorded. The analytical parameters and the procedure of the electrode regeneration and activation were optimized. The calibration curve of monobutyltin in the range 0.02–0.30 mg L^?1 is linear (r=0.9973). The detection limit for 5 s of preconcentration, calculated as 3σ of the blank was equal to 0.004 mg L^?1, repeatability of the peak current was 1.8 % (n=5). Repeatability and sensitivity of monobutyltin determination depends strongly on the analyzed solution properties, measurement conditions and the working electrode quality. The proposed procedure was tested by means of monobutyltin determination in tap waters.     

Electrocatalysis via Direct Electrochemistry of Myoglobin Immobilized on Colloidal Gold Nanoparticles

The direct electron transfer between immobilized myoglobin (Mb) and colloidal gold modified carbon paste electrode was studied. The Mb immobilized on the colloidal gold nanoparticles displayed a pair of redox peaks in 0.1 M pH 7.0 PBS with a formal potential of –(0.108 ± 0.002) V (vs. NHE). The response showed a surface‐controlled electrode process with an electron transfer rate constant of (26.7 ± 3.7) s ^?1 at scan rates from 10 to 100 mV s^?1 and a diffusion‐controlled process involving the diffusion of proton at scan rates more than 100 mV s^?1. The immobilized Mb maintained its activity and could electrocatalyze the reduction of both hydrogen peroxide and nitrite. Thus, the novel renewable reagentless sensors for hydrogen peroxide and nitrite were developed, respectively. The activity of Mb with respect to the pseudo peroxidase with a K_M^app value of 0.65 mM could respond linearly to hydrogen peroxide concentration from 4.6 to 28 μM. The sensor exhibited a fast amperometric response to NO₂^? reduction and reached 93% of steady‐state current within 5 s. The linear range for NO₂^? determination was from 8.0 to 112 μM with a detection limit of 0.7 μM at 3σ.     

Disposable screen-printed ring disk carbon electrode coupled with wall-jet electrogenerated iodine for flow injection analysis of arsenic(III)

We report here a wall-jet electrogenerated iodine approach for sensitive detection of arsenite (As^III) by using a disposable screen-printed ring disk carbon electrode. Iodide (I⁻) is first oxidized to iodine (I₂) at the disk electrode; the electrogenerated I₂ can be effectively reduced back to I⁻ in the presence of As^III. The inhibited reduction current of I₂ to I⁻ can thus be monitored at the ring electrode and used for As^III analysis. Various factors influencing the flow injection analysis (FIA) of As^III were thoroughly investigated in this study. Under the optimized conditions, a linear calibration plot up to 10 μM with a detection limit (S/N = 3) of 70 nM was obtained by using 50 μM KI as the mobile phase in FIA. Practical utility of the proposed method was demonstrated to detect As^III in “Blackfoot” disease endemic village groundwater from southwestern coast area of Taiwan (Pei-Men).     

Flow Injection Analysis of Sulfide Using a Cinder/Tetracyano Nikelate Modified Screen‐Printed Electrode

Flow injection analysis (FIA) of sulfide is presented using a screen‐printed carbon electrode modified with a cinder/tetracyano nickelate hybrid (designated as cinder/NiTcSPE). Hybridization of NiTc was achieved in iron‐enriched industrial waste cinder material through the bimetallic formation of Fe^III[Ni^II(CN)₄]. The electrocatalytic oxidation of sulfide is mediated by the higher oxidation state of Ni in this hybrid‐bimetallic complex. The system shows a detection limit (S/N=3) of 0.06 μM and a linear working range up to 1 mM in pH 10, 0.1 M KCl solution. Taking into account the relatively low volatility of the analyte in alkaline conditions, the system is ideally suited for the accurate detection of sulfide. The response of the electrode to sulfide is highly reproducible, thereby offering the potential development of a disposable amperometric sensor for sulfide. Selective detection of sulfide in cigarette smoke is presented in this study as an example of a real sample application.     

Renewable Surface Sol‐gel Derived Carbon Ceramic Electrode Modified with Copper Complex and Its Application as an Amperometric Sensor for Bromate Detection

A sol‐gel technique was used for the preparation of a three dimensional carbon composite electrode modified with [Cu(bpy)₂]Br₂ complex. A reversible redox couple of Cu(II)/Cu(I) is observed at the electrode surface. The electrochemical behavior and stability of the modified electrode was characterized by cyclic voltammetry. The charge transfer coefficient (α) and charge transfer rate constant (K_s) for the modified electrode were determined by cyclic voltammetry, which were found to be 0.46 and 14.2 s^?1, respectively. The modified electrode showed excellent catalytic activity toward bromate reduction at significantly reduced overpotentials and can be used successfully for amperometric detection of bromate. Under the optimized conditions, the calibration plots are linear in the concentration range 0.5 μM ?200μM. Detection limit (signal to noise is 3) and sensitivity were found to be 0.1 μM and 20 nA / μM, respectively. These analytical parameters compare favorably with those obtained with modern analytical techniques. The modified carbon ceramic electrode doped with Cu‐Complex shows a good reproducibility, a short response time (t<2 s), remarkable long term stability (>4 months) and especially good surface renewability by simple mechanical polishing (RSD for 6 successive polishing is 1.5%).     

Comparison of Boron‐Doped Diamond and Glassy Carbon Electrodes for Determination of Procaine Hydrochloride

The electrochemical oxidation of procaine hydrochloride (PC?HCL, 2‐diethylaminoethyl 4‐aminobenzoate hydrochloride) was investigated at as‐deposited boron‐doped diamond (ad‐BDD) electrode, anodically oxidized BDD (ao‐BDD) electrode and glassy carbon (GC) electrode using cyclic voltammetry (CV). Well‐defined cyclic voltammograms were obtained for PC?HCL oxidation with high signal‐to‐background (S/B) ratio, low tendency for adsorption, good reproducibility and long‐term stability at ad‐BDD electrode, demonstrating its superior electrochemical behavior and significant advantages in contrast to ao‐BDD and GC electrode. At 100 μM PC?HCL, the voltammetric S/B ratio was nearly one order of magnitude higher at an ad‐BDD electrode than that at a GC electrode. In a separate set of experiments for oxidation of 100 μM PC?HCL, 96%, 92% and 84% of the initial oxidation peak current was retained at the ad‐BDD, ao‐BDD and GC electrode, respectively, by stirring the solution after the tenth cycle. The current response was linearly proportional to the square root of the scan rate within the range 10–1000 mV s^?1 in 10 μM PC?HCL solutions, indicating that the oxidation process was diffusion‐controlled with negligible adsorption at an ad‐BDD surface. The good linearity was observed for a concentration range from 5 to 200 μM with a linear equation of y=0.03517x+0.65346 (r=0.999), and the detection limit was 0.5 μM for oxidation of PC?HCL at the ad‐BDD electrode. The ad‐BDD electrode could maintain 100% of its original activity after intermittent use for 3 months.     

CuAg nanoparticles formed in situ on electrochemically pre‐anodized screen‐printed carbon electrodes for the detection of nitrate and nitrite anions

CuAg nanoparticles (CuAgNPs) were electrochemically formed in situ on pre‐anodized, screen‐printed carbon electrodes (SPCEs) that possessed many oxygen‐containing functional groups capable of adsorbing metal ions, namely Cu²⁺ and Ag⁺. Pre‐anodization was achieved using continuous cyclic voltammetry in the range of potential 0.3–2.0 V under a scan rate of 50 mV/s. Cu²⁺ and Ag⁺ ions were adsorbed on the pre‐anodized SPCE by immersing the electrode in solutions containing both metal ions, and then CuAgNPs were formed in situ via electrochemical reduction in a deaerated, neat NaClO₄ solution after the electrode was ultrasonicated to remove physically adsorbed metal ions. Although CuNPs showed higher activity than AgNPs toward both nitrate (NO₃⁻) and nitrite (NO₂⁻) ions, the instability of CuNPs hindered the application, so CuAgNPs were employed to achieve a compromise between sensitivity and stability. The SPCE/anodized/CuAgNP electrodes showed activity toward the electrochemical reduction of NO₃⁻ and NO₂⁻, respectively, with the limit of detection (LOD) of 15.6 μM (0.97 ppm) and 11.1 μM (0.51 ppm), which is sufficient to fit the allowed values (50 and 3 ppm, respectively) in drinking water as suggested by the World Health Organization (WHO).     

Flow Injection Amperometric Analysis of H2O2 at Platinum Nanoparticles Modified Pencil Graphite Electrode

A Pt nanoparticle modified Pencil Graphite Electrode (PGE) was proposed for the electrocatalytic oxidation and non‐enzymatic determination of H₂O₂ in Flow Injection Analysis (FIA) system. Platinum nanoparticles (PtNPs) electrochemically deposited on pretreated PGE (p.PGE) surface by recording cyclic voltammograms of 1.0 mM of H₂PtCl₆ solution in 0.10 M KCl at scan rate of 50 mV s⁻¹ for 30 cycles. Cyclic voltammograms show that the oxidation peak potential of H₂O₂ shifts from about +700 mV at bare PGE to +50 mV at PtNPs/p.PGE vs. Ag/AgCl /KCl (sat.). It can be concluded that PtNPs/p.PGE exhibits a good electrocatalytic activity towards oxidation of H₂O₂. Then, FI amperometric analysis of H₂O₂ was performed under optimized conditions using a new homemade electrochemical flow cell which was constructed for PGE. Linear range was found as 2.5 μM to 750.0 μM H₂O₂ with a detection limit of 0.73 μM (based on S_b/m of 3). As a result, this study shows the first study on the FI amperometric determination of H₂O₂ at PtNPs/p.PGE which exhibits a simple, low cost, commercially available, disposable sensor for H₂O₂ detection. The proposed electrode was successfully applied to determination of H₂O₂ in real sample.     

Voltammetric Determination of Uric Acid at a Fullerene‐C60‐Modified Glassy Carbon Electrode

Glassy carbon electrode modified by microcrystals of fullerene‐C₆₀ mediates the voltammetric determination of uric acid (UA) in the presence of ascorbic acid (AA). Interference of AA was overcome owing to the ability of pretreated fullerene‐C₆₀‐modified glassy carbon electrode. Based on its strong catalytic function towards the oxidation of UA and AA, the overlapping voltammetric response of uric acid and ascorbic acid is resolved into two well‐defined voltammetric peaks with lowered oxidation potential and enhanced oxidation currents under conditions of both linear sweep voltammetry (LSV) and Osteryoung square‐wave voltammetry (OSWV). At pH 7.2, a linear calibration graph is obtained for UA in linear sweep voltammetry over the range from 0.5 μM to 700 μM with a correlation coefficient of 0.9904 and a sensitivity of 0.0215 μA μM^?1 . The detection limit (3σ) is 0.2 μM for standard solution. AA in less than four fold excess does not interfere. The sensitivity and detection limit in OSWV were found as 0.0255 μA μM^?1 and 0.12 μM, for standard solution respectively. The presence of physiologically common interferents (i.e. adenine, hypoxanthine and xanthine) negligibly affects the response of UA. The fullerene‐C₆₀‐modified electrode exhibited a stable, selective and sensitive response to uric acid in the presence of interferents.     

Simultaneous Determination of Nitrite and Hydrogen Peroxide Using Hemoglobin Modified Pencil Lead Electrode as a Novel Biosensor: Application to the Analysis of Mother’s Milk

In the present paper simultaneous determination of nitrite and hydrogen peroxide using hemoglobin modified pencil lead electrode (Hb/PLE) prepared by a simple and rapid electroless method was described. In the first part of the work the reduction of NO₂ and H₂O₂ at the modified electrode was investigated by cyclic voltammetry. Then under optimal conditions using differential pulse voltammetry, the biosensor could be used for the determination of H₂O₂ at concentration ranging from 5 to 240 M and NO₂ at concentration ranging from 10 to 240 M. The detection limits were 3×10^?6 and 5×10^?6 M, for NO₂ and H₂O₂ respectively. Differential pulse voltammetry also used for the simultaneous determination of NO₂ and H₂O₂. This modified electrode successfully used for the determination of NO₂ and H₂O₂ in tap water and mother’s milk samples.     

Pencil Lead Electrode Modified with Hemoglobin Film as a Novel Biosensor for Nitrite Determination

In the present paper, the electrochemical reduction of nitrite at a hemoglobin modified pencil lead electrode (Hb/PLE) is described. The electrochemical properties of nitrite were studied by cyclic voltammetry and chronoamperometry. Results showed that the hemoglobin film has an excellent electrochemical activity towards the reduction of nitrite. By using voltammetric and chronoamperometric methods, α, n_α and n were calculated. Then the ability of the electrode for nitrite determination was investigated using differential pulse voltammetry. The electrocatalytic reduction peak currents were found to be linear with the nitrite concentration in the range from 10 to 220 µM with a detection limit of 5 µM. The relative standard deviation is 2 % for 3 successive determinations of a 100 µM nitrite solution. This modified electrode was successfully used for the detection of low amounts of NO₂^? in spinach sample and a spiked sample of tap water.     

Development of an Enzymeless/Mediatorless Glucose Sensor Using Ruthenium Oxide‐Prussian Blue Combinative Analogue

Presented in this work is the first step towards an enzymeless/mediatorless glucose sensor. We first observed remarkable electrocatalytic oxidation of glucose using combinative ruthenium oxide (RuOx)‐Prussian blue (PB) analogues (designated as mvRuOx‐RuCN, mv: mixed valent) at ca. 1.1 V (vs. Ag/AgCl) in acidic media (pH 2 Na₂SO₄/H₂SO₄). Individual RuOx and PB analogs failed to give any such catalytic response. A high ruthenium oxidation state (i.e., oxy/hydroxy‐Ru^VII, E°≈1.4 V vs. RHE), normally occurring in strong alkaline conditions at RuOx‐based electrodes, was electrogenerated and stabilized (without any conventional disproportionation reaction) in the mvRuOx‐RuCN matrix for glucose catalysis. Detail X‐ray photoelectron spectroscopic studies can fully support the observation. The catalyst was chemically modified onto a disposable screen‐printed carbon electrode and employed for the amperometric detection of glucose via flow injection analysis (FIA). This system has a linear detection range of 0.3–20 mM with a detection limit and sensitivity of 40 μM (S/N=3) and 6.2 μA/(mM cm²), respectively, for glucose. Further steps towards the elimination of interference and the extendibility to neutral pHs were addressed.     

Flow‐Injection Pulsed‐Amperometric Determination of Free Glycerol in Biodiesel at a Gold Electrode

This work reports the highly‐sensitive amperometric determination of free glycerol in biodiesel at a gold electrode adapted in a flow‐injection analysis (FIA) cell. The amperometric method involved the continuous application of three sequential pulses to the working electrode (+250 mV, +700 mV, and ?200 mV, for 100 ms each). This sequence of potential pulses eliminated electrode passivation and dramatically increased the analytical signal. The proposed FIA‐amperometric method presented low relative standard deviation between injections (1.5 %, n=15), high analytical frequency (85 h^?1), satisfactory recovery values (93–118 %) for spiked samples, wide linear range (from 1 to 300 µmol L^?1), and low detection limit (0.5 µmol L^?1).     

Design of the Fluoride Ion-Selective Electrode as Tubular Detector for Flow Injection Analysis

ABSTRACT

Design of the fluoride ion-selective electrode (FISE) as the tubular detector used in the flow injection analysis (FIA) has been described. Among other things, this design makes it possible to use various internal contacts. The effect of pH on peak height and detection limit in the pH range from 2.8 to 8.0 has been examined. The effect of flow rate and sample injection volume on peak height and range of linear response has also been examined. The flow rates range from 0.56 mL/min to 4.05 mL/min, while the injection volumes are 100 and 200 μL. The optimum conditions are carrier solution (0.1 M KNO₃ buffer pH 4 and 10^-6 M NaF), flow rate 1.54 mL/min and sample injection volume 100 μL.

Applicability of the FISE as the tubular detector in determination of Fe(III)-ions and AI(III)-ions by flow infection analysis has been examined at pH values of 2.8 and 3.4.     

Chemically Modified Carbon Paste Electrode for Determination of Sulfate Ion by Potentiometric Method

Four Schiff base complexes of different metal ions, M=Cr(III), Mn(III), Fe(III), and Co(III), were studied to characterize their ability as sulfate ion carriers in carbon paste electrode (CPE). The modified CPE electrode with Schiff base complex of Cr(III), N,N′‐ethylenebis(5‐hydroxysalicylideneiminato) chromium(III) Chloride, showed good response characteristics to SO₄^2? ion. The proposed electrode exhibits a Nernstian slope of 28.9±0.4 mV per decade for SO₄^2? ion over a wide concentration range from 1.5×10^?6?4.8×10^?2 M, with a detection limit of 9.0×10^?7 M. The CPE electrode manifested advantages of relatively fast response time, suitable reproducibility and life time and, most important, good potentiometric selectivity relative to a wide variety of other common inorganic anions. The potentiometric response of the electrode is independent of the pH of the test solution in the pH range 4.0–9.0. The proposed electrode was used as an indicator electrode in potentiometric titration of sulfate with Ba²⁺ ion, the determination of zinc in zinc sulfate tablet and also determination of sulfate content of a mineral water sample.     

Fabrication of Photoelectrochemical Glucose Biosensor in Flow Injection Analysis System Using ZnS/CdS‐Carbon Nanotube Nanocomposite Electrode

In this work, a photoamperometric glucose biosensor based on glucose oxidase (GODx) was developed in flow injection analysis (FIA) system using ZnS‐CdS quantum dot (QD) modified multiwalled carbon nanotube/glassy carbon electrode (ZnS‐CdS/MWCNT/GCE). Cyclic voltammograms of the proposed electrode (GODx/ZnS‐CdS/MWCNT/GCE) showed a pair of well‐defined reversible redox peak attributing that direct electron transfer between the protein and electrode. The current of the reduction peak became more cathodic in the presence of O₂ due to the electrocatalytic activity of the electrode towards the reduction of dissolved O₂, but reduction current shifted to a less negative value upon addition of glucose in the solution. The obtained CV currents were affected by the irradiation of the electrode surface. Thus, the photoelectrochemical biosensing of glucose in the FIA system was studied by monitoring of the changes in the electrocatalyzed reduction peak current of dissolved O₂ at the proposed electrode dependent on glucose concentration. The proposed photoelectrochemical FIA method has a linear response to glucose ranging from of 0.01 to 1.0 mM with detection limit of 3.0 μM under optimized conditions. Photoelectrochemical biosensor was successfully fabricated in FIA system for selective, sensitive and repeatable detection of glucose and has been satisfactorily applied to determination of glucose in real sample.     

Carbon nanotube composite PVC coated stainless steel disc electrode for detection of Ga(III)

This study demonstrates the application of the composite of multi-walled carbon nanotube polyvinylchloride (MWCNT-PVC) based on Bismarck Brown R for gallium sensor. MWCNT has a role to enhance the hydrophobicity of the membrane, which leads to a more stable potential signal. In addition by applying polypyrrol on the surface of this sensor a reduction in the drift of potential occurred and equilibrium potential was achieved faster. Compared to previous studies, using a stainless steel disc instead of a wire electrode causes to obtain an easily and more homogeneous coated electrode. The sensor shows a good Nernstian slope of 19.70?±?0.37?mV?decade^?1 in a wide linear range concentration of 1.0?×?10^?7 to 1.0?×?10^?2?M of Ga(NO₃)₃. The detection limit of this electrode was 7.7?×?10^?8?M of Ga(NO₃)₃. This proposed sensor is applicable in a wide pH range of 2 to 8. It has a short response time of about 8?s and has a good selectivity over twenty four various metal ions. The practical analytical utility of this electrode is demonstrated by measurement of Ga(III) in rock and different water samples.     

Simple and Fast Determination of Warfarin in Pharmaceutical Samples Using Boron‐doped Diamond Electrode in BIA and FIA Systems with Multiple Pulse Amperometric Detection

This paper proposes the use of the boron‐doped diamond electrode (BDDE) in flow and batch injection analysis (FIA and BIA) systems with multiple‐pulse amperometric (MPA) detection for the determination of warfarin (WA) in pharmaceutical formulations. The electrochemical behavior of WA obtained by cyclic voltammetry (CV) in 0.1 mol L⁻¹ phosphate buffer shows an irreversible oxidation process at +1.0 V (vs Ag/AgCl). The MPA was based on the application of two sequential potential pulses as a function of time on BDDE: (1) for WA detection at +1.2 V/100 ms and; (2) for electrode surface cleaning at −0.2 V/200 ms. Both hydrodynamic systems (FIA‐MPA and BIA‐MPA) used for WA determination achieved high precision (with relative standard deviations around 2 %, n =10), wide linear range (2.0−400.0 μmol L⁻¹), low limits of detection (0.5 μmol L⁻¹) and good analytical frequency (94 h⁻¹ for FIA and 130 h⁻¹ for BIA). The WA determination made by the proposed methods was compared to the official spectrophotometric method. The FIA‐MPA and BIA‐MPA methods are simple and fast, being an attractive option for WA routine analysis in pharmaceutical industries.