Department of Analytical Chemistry The Department of analytical chemistry is a leading center for education and research in analytical chemistry. With expert faculty, modern facilities, and a strong focus on innovation, we prepare students for successful careers and academic excellence. Join us and be part of a dynamic learning community shaping the future.
filter by: Publication Year
(Descending) Articles
Journal of the Electrochemical Society (00134651) 144(8)pp. 2652-2657
Ni-Zn-P electrodes were prepared by subsequent deposition of Ni, Ni-P, and Ni-Zn-P layers. The topmost Ni-Zn-P layer was obtained by gradual addition of zinc to the plating bath. The obtained electrodes are more stable and more active toward the hydrogen evolution reaction than Ni-Zn alloys. They are characterized by low Tafel slopes and large surface roughness of 104. They may be attractive candidates for the alkaline water electrolysis.
Journal of the Electrochemical Society (00134651) 144(2)pp. 511-519
The hydrogen evolution reaction (HER) was studied on Ni-P electrodes containing 8 to 30 atomic percent P prepared by galvanostatic deposition. The electrodes were studied directly after preparation or after pretreatment by heating, leaching in HF solution, anodic oxidation, or potential cycling in the solution. The activity of these electrodes depended on the method of preparation and phosphorous content. The activity was higher for the materials deposited at lower temperatures and for those containing smaller amounts of phosphorous. The mechanism of the hydrogen evolution reaction was studied in 1 M NaOH, and the kinetic parameters were determined using steady-state polarization and electrochemical impedance spectroscopy techniques.
Journal of the Electrochemical Society (00134651) 145(7)pp. 2219-2225
Nickel-molybdenum-phosphorous electrodes were prepared by electrodeposition, and their activity for the hydrogen evolution reaction was studied in 1 M NaOH using electrochemical impedance spectroscopy and steady-state polarization techniques. Active and stable electrodes were obtained by deposition of three successive layers of Ni, Ni-P, and Ni-Mo-P and creating a concentration gradient in the topmost layer. It was found that the increase in electrode activity was due to increases in both the surface roughness and the intrinsic activity, as compared with Ni-P, Ni-Mo, and Ni electrodes. The reaction mechanism and the kinetic parameters were determined.
Journal of Applied Electrochemistry (15728838) 29(8)pp. 979-986
The surface roughness of porous Ni-Zn-P electrodes was studied in 1 M NaOH using in situ electrochemical techniques: ratio of the polarization current densities, electrochemical impedance spectroscopy, cyclic voltammetry, coulometric oxidation of the surface, and a new technique of a CO molecular probe. The obtained surface roughness was about 5.5×103. Good agreement was observed between the results obtained by all these techniques.
Journal of New Materials for Electrochemical Systems (14802422) 8(3)pp. 213-220
The aqueous suspended RuCl3 was coated into the pores of microporous Ni-Zn-P alloy and thermally decomposed at 400°C in an open furnace to produce composite electrodes (Ni-Zn-P-RuO2). The microporous alloy was prepared via a three-step layer-by-layer galvanostatic deposition. The electrocatalytic behavior of the electrode was investigated in the hydrogen evolution reaction (HER), by steady state polarization Tafel curves, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) in 1M NaOH solution at 25°C. The kinetics as Tafel slopes, double layer capacitances, and charge transfer resistances towards the HER were evaluated. The electrode is characterized by (i) a large real surface area of three orders of magnitude obtained from CV and EIS measurements, and (ii) high physical and electrochemical stability of RuO2 dispersed into the surface. The poisoning effect of cyanide ion on the HER was also studied by EIS. This study allowed us to select properly data for kinetics approximation. © J. New. Mat. Electrochem. Systems.
Surface and Coatings Technology (02578972) 198(1-3 SPEC. ISS.)pp. 123-128
Fabrication and electrochemical characterization of a self-assembled three layers modified gold electrode is described. The modification involves a three-step method; (i) preparation of cysteamine self-assembled monolayer, Au-CA, (ii) activation of Au-CA by glutaraldehyde to prepare Au-CA-GA, (iii) modification of Au-CA-GA by 2-Aminoethyl dihydrogen phosphate to functionalize the surface by phosphate groups, Au-CA-GA-AEDP. The resulting thin film modified electrode was tested successfully to recognize uranyl cations (UO22+) in aqueous solution. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to trace events in each step. The high affinity of the film towards the UO22+ was confirmed by EIS and CV results. The EIS data allowed recognition of UO22+ based on variation of the charge-transfer resistance (Rct) of the film as a function of the cation concentration. A dynamic range with more than three orders of magnitude was obtained. © 2004 Elsevier B.V. All rights reserved.
Bioelectrochemistry (15675394) 69(2)pp. 201-208
A method is developed for quantitative determination of glucose using electrochemical impedance spectroscopy (EIS). The method is based on immobilized glucose oxidase (GOx) on the topside of gold mercaptopropionic acid self-assembled monolayers (Au-MPA-GOx SAMs) electrode and mediation of electron transfer by parabenzoquinone (PBQ). The PBQ is reduced to hydroquinone (H2Q), which in turn is oxidized at Au electrode in diffusion layer. An increase in the glucose concentration results in an increase in the diffusion current density of the H2Q oxidation, which corresponds to a decrease in the faradaic charge transfer resistance (Rct) obtained from the EIS measurements. Glucose is quantified from linear variation of the sensor response (1/Rct) as a function of glucose concentration in solution. The method is straightforward and nondestructive. The dynamic range for determination of glucose is extended to more than two orders of magnitude. A detection limit of 15.6 μM with a sensitivity of 9.66 × 10- 7 Ω- 1 mM- 1 is obtained. © 2006 Elsevier B.V. All rights reserved.
Talanta (00399140) 69(3)pp. 741-746
Fabrication and application of a voltammetric sensor based on gold 2-mercaptobenzothiazole self-assembled monolayer (Au-MBT SAM) for determination of silver ion is described. Preliminary experiments were performed to characterize the monolayer. The surface pKa determined for the MBT monolayer is 7.0. This value was obtained by impedimetric titration of the monolayer in the presence of Fe(CN)6 3-/4- as a redox probe. The extent of surface coverage was evaluated as 1.52 × 10-9 mol cm-2 based on charged consumed for reductive desorption of the monolayer in the 0.50 M NaOH solution. Then the sensor was used for determination of Ag(I) by square wave voltammetry. The parameters affecting the sensor response, such as pH and supporting electrolyte, were optimized. A dynamic calibration curve with two linear parts was obtained in the concentration ranges of 5 × 10-8-8 × 10-7 and 1 × 10-6-1 × 10-5 M of Ag(I). The detection limit adopted from cathodic striping square wave voltammetry was as 1 × 10-8 M for n = 7. Furthermore, the effect of potential interfering ions on the determination of Ag(I) was studied, and an appropriate method was used for the elimination of this effect. © 2005 Elsevier B.V. All rights reserved.
Analytical Chemistry (15206882) 78(14)pp. 4957-4963
Fabrication and electrochemical characterization of a novel nanosensor for determination of Cu2+ in subnanomolar concentrations is described. The sensor is based on gold cysteamine self-assembled monolayer functionalized with salicylaldehyde by means of Schiff's base formation. Cyclic voltammetry, Electrochemical impedance spectroscopy (EIS), and electrochemical quartz crystal microbalance were used to probe the fabrication and characterization of the modified electrode. The sensor was used for quantitative determination of Cu2+ by the EIS in the presence of parabenzoquinone in comparison with stripping Osteryoung square wave voltammetry (OSWV). The attractive ability of the sensor to efficiently preconcentrate trace amounts of Cu2+ allowed a simple and reproducible method for copper determination. A wide range linear calibration curve was observed, 5.0 × 10-10-5.0 × 10-6 and 5.0 × 10-10-5.0 × 10-6 M Cu2+, by using the EIS and OSWV, respectively. Moreover, the sensor presented excellent stability with lower than 10% change in the response, as tested for more than three months daily experiments, and a high repeatability with relative standard deviations of 6.1 and 4.6% obtained for a series of eight successive measurements in 5.0 × 10-7 M Cu2+ solution, by the EIS and OSWV, respectively. © 2006 American Chemical Society.
Sensors and Actuators B: Chemical (09254005) 115(2)pp. 614-621
A monolayers of cysteamine (CA) was prepared on a polycrystalline gold electrode through self-assembly procedure to produce a gold cysteamine self-assembled monolayers (Au-CA SAMs) modified electrode. Characterization of the modified electrode was performed by using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The EIS was used to evaluate pKa of the adsorbed CA on the gold surface, and a value of 7.6 was obtained for the Au-CA surface pKa. The charged terminal groups of monolayers served for determination of dopamine (DA) in the presence of high concentration of ascorbic acid (AA) using differential pulse voltammetry (DPV). Well-separated DA and AA voltammetric waves (∼330 mV) were observed at the Au-CA SAMs electrodes in an acidic solution. A calibration curve with two linear parts was obtained for DA, 6.00 × 10-6 to 3.84 × 10-4 M and 3.36 × 10-4 to 9.50 × 10-3 M, with correlation coefficients 0.997 and 0.992, respectively. The detection limit for DA was found to be 2.31 μM in the presence of 1.0 mM AA. The apparent charge transfer rate constants (kapp) of AA and DA were evaluated by using EIS measurements on the modified electrode as 44.0 cm s-1 × 10-8 cm s-1 and 2.45 cm s-1 × 10-8 cm s-1, respectively. © 2005 Elsevier B.V. All rights reserved.
Analytica Chimica Acta (00032670) 562(2)pp. 223-228
A phosphate functionalized cysteamine self-assembled monolayer based on gold electrode is designed for uranyl ion (UO22+) detection. The response of the modified electrode is studied by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. The EIS data are approximated using constant phase element (CPE) model from which kinetic and analytical parameters are evaluated. Uranyl ion is recognized based on blocking effect against charge transfer between p-benzoquinone as a probe and the modified electrode. This effect is detected from linear variation of charge transfer resistance (Rct) as a function of UO2 2+ concentration. From the analysis of the EIS data and approximated parameters, a method is developed for UO22+ determination based on impedimetric measurements. © 2006 Elsevier B.V. All rights reserved.
Electrochimica Acta (00134686) 52(24)pp. 7051-7060
Comparative electrochemical behavior of self-assembled monolayers (SAMs) of three heteroaromatic thiols, 2-mercaptobenzoxazole (MBO), 2-mercaptobenzothiazole (MBT), and 2-mercaptobenzimidazole (MBI) are investigated by means of cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The electrochemical characteristics of the electrode/solution interface are considerably and differently affected by thiols constructing the SAMs. The consumed charges for reductive desorption of SAMs, which is criterion for the amount of chemically adsorbed thiol, are significantly different for these three SAMs, specially for MBT, implying that SAM of MBT is formed through both sulfur atoms; the thiol sulfur and skeleton sulfur of the thiazole ring. Desorption potentials of the SAMs have shown the following order for strength of gold-sulfur bond: MBT > MBO > MBI. Activity of the three SAMs as pH-sensitive interfaces was also investigated and their surface-pKa values derived from the EIS measurements showed this order for acidic strength of SAMs: MBO > MBT > MBI. This is the same order expected due to the difference in electronegativity of the O, S, and N heteroatoms, and confirms that the most electron-rich ring imidazole is attached to the benzene ring of MBI. A comparison of the interfacial charge transfer resistance variation as a function of gold immersion time in thiols solution reveals that kinetics of Au-MBT assembly is different from those of two others and confirms formation of Au-MBT SAM via both sulfur atoms of MBT. © 2007 Elsevier Ltd. All rights reserved.
Journal Of The Iranian Chemical Society (1735207X) 4(2)pp. 221-228
Electrochemical characterization and application of nickel ruthenium dioxide (Ni-RuO2) as a pH sensor for the determination of petroleum oil acid number is described. The sensor consists of RuCl3 thermally decomposed onto the upper side of a polycrystalline nickel electrode at 400°C in an open furnace. The advantages of the sensor are: (i) easy preparation, (ii) fast response in a large pH range, (iii) high physical and chemical stability, and (iv) excellent reproducibility as determined by the reproducible linear variation of charge transfer resistance (Rct) as a function of overpotential (η) obtained by electrochemical impedance spectroscopy (EIS), and the Nernstian slope of the electrode potential in a wide range of pH (1.5-12.5) obtained by potentiometric measurements. The potentiometric selectivity coefficients of the sensor toward some anions and cations were evaluated in aqueous solution. The characterized Ni-RuO2 pH sensor was successfully tested for the determination of petroleum oil acid number.
Sensors and Actuators B: Chemical (09254005) 126(2)pp. 415-423
A new method is developed, for direct coupling of enzymes on gold thiol self-assembled monolayers, based on glucose oxidase as a model enzyme and gold mercaptosuccinic anhydride self-assembled monolayer as a platform. The immobilization method is simple and fast, and enzyme is immobilized very close to the gold electrode surface. Preparation steps and the biosensor response to glucose are monitored by cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and chronoamperometry. The relative differences between the slopes and intercepts of the current and conventional methods, using EDC/NHS activators for immobilization, are 10 and 8% for five-time measurements of each calibration curve obtained by chronoamperometry. The EIS data are approximated based on appropriate electronic equivalent circuit models and charge transfer resistances (Rct) are extracted from which a wide range linear calibration curve is obtained using 1/Rct versus glucose concentration. In addition, the analytical method is improved based on the EIS abilities allowing decreasing data acquisition time by a factor of 15. © 2007 Elsevier B.V. All rights reserved.
Journal of Power Sources (03787753) 164(2)pp. 890-895
The steady-state and anodic corrosion of Pb-0.17 wt.% Ca-0.88 wt.% Sn, and Pb-0.17 wt.% Ca-0.88 wt.% Sn-0.06 wt.% Li alloys in 4.5 M H2SO4 at 25 °C were studied using cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy. The experimental results show that the lithium added to Pb-Ca-Sn alloy increases corrosion resistance in equilibrium potential and inhibits the growth of the anodic corrosion layer. © 2006 Elsevier B.V. All rights reserved.
Analytica Chimica Acta (00032670) 587(2)pp. 254-262
Electrochemical characterization of gold cysteamine self-assembled monolayer, in situ functionalized with ethylenediaminetetraacetic acid (Au-CA-EDTA SAM), is described by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Osteryoung square wave voltammetry (OSWV). The results obtained by EIS and CV, in the presence of [Fe(CN)6]3-/4- redox probe, show that EDTA is successfully grafted to the surface of Au-CA electrode. Reproducible and reversible variation of the Rct and ΔEp as a function of solution pH show that Au-CA-EDTA SAM is stable in a wide range of pH and potentials. Accumulation of the Pb2+ and Cu2+ ions on the Au-CA-EDTA SAM electrode is investigated using faradaic currents or impedimetric effects measured by OSWV and EIS, respectively. These results reveal the presence of active complexing functional groups of EDTA on the surface, and thus, the formation of Au-CA-EDTA SAM electrode. The new sensor responds to the Pb2+ and Cu2+ separately and simultaneously in a wide linear range of concentrations. © 2007 Elsevier B.V. All rights reserved.
Electrochimica Acta (00134686) 53(2)pp. 426-433
Ternary nickel-iron-carbon (Ni-Fe-C) alloys have been characterized by means of microstructural and electrochemical techniques in view of their possible applications as electrocatalytic materials for hydrogen evolution reaction (HER). The electrochemical efficiency of the electrodes has been evaluated on the basis of electrochemical data obtained from the steady-state polarization Tafel curves, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) in 1 M NaOH solution at 298 K in the absence and presence of cyanide ion as the poison. Steady-state polarization Tafel curves showed that the Ni-Fe-C electrodes were apparently active for the HER. Therefore, the EIS studies were performed to obtain more precise data and find the source of activity. A surface roughness of more than three orders of magnitude was observed for Ni62Fe35C3 electrode. The rate constants of the forward and backward reactions of Volmer and Heyrovský steps were estimated by using Tafel-impedance data. A comparison between the values obtained for Rf by the EIS and the values obtained for k2 by approximation of Tafel-impedance data revealed that the increase in activity of Ni62Fe35C3 electrode toward the HER was partially (20%) originated from increase in the surface roughness, and mostly (80%) from increase in the intrinsic activity. © 2007 Elsevier Ltd. All rights reserved.
Analytica Chimica Acta (00032670) 601(2)pp. 164-171
Preparation and application of gold 2-mercaptosuccinic acid self-assembled monolayer (Au-MSA SAM) electrode for determination of iron(III) in the presence of iron(II) is described by cyclic voltammetry, electrochemical impedance spectroscopy, and Osteryoung square wave voltammetry. The square wave voltammograms showed a sharp peak around positive potentials +0.250 V that was used for construction of the calibration curve. Parameters influencing the method were optimized. A linear range calibration curve from 1.0 × 10-10 to 6.0 × 10-9 M iron(III) with a detection limit of 3.0 × 10-11 M and relative standard deviation (R.S.D.) of 6.5% for n = 8 at 1.0 × 10-9 M iron(III) was observed in the best conditions. Possible interferences from the coexisting ions were also investigated. The results demonstrated that sensor could be used for determination of iron(III) in the presence of various ions. The validity of the method and applicability of the sensor were successfully tested by determining of iron(III) in natural waters (tap and mineral waters) and in a pharmaceutical sample (Venofer® ampoule) without interference from sample matrix. The experimental data are presented and discussed from which the new sensor is characterized. © 2007 Elsevier B.V. All rights reserved.
Electrochimica Acta (00134686) 53(12)pp. 4185-4192
Electrocatalytic activity of a new catalyst toward the oxidation reaction of hydroquinone as a model compound is described. The catalyst was formed by immobilizing metal cations on the topside of a gold-5-amino-2-mercaptobenzimidazole, self-assembled monolayer (Au-5A2MBI-Mn+ SAM, Mn+: Cu2+, Ag+) electrode. Preparation steps and the electrocatalytic activity of the catalyst were studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The EIS data were approximated by appropriate electronic equivalent circuit models from which kinetic parameters, such as charge transfer resistance, double layer capacitance, and apparent rate constant (kapp), were estimated. Excellent activity was observed for Au-5A2MBI-Ag+ SAM with the following order: Au-5A2MBI-Ag+ > Au-5A2MBI-Cu2+ > Au-5A2MBI, after testing many modified electrodes. The increased activity originates from a modification of the Au-5A2MBI structure by mediating the effect of Ag+. This behavior was understood from significant increases in the kapp without significant changes in the double layer capacitance. © 2008 Elsevier Ltd. All rights reserved.
International Journal of Hydrogen Energy (03603199) 33(10)pp. 2468-2476
Kinetics of hydrogen evolution reaction (HER) was studied in 1 M NaOH at 298 K on nickel-phosphorous-carbon (Ni81 P16 C3) composite electrode. Evaluation of the electrode activities was carried out by steady-state polarization Tafel curves, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). The kinetic parameters obtained by Tafel curves revealed that Ni-P composites modified by incorporation of carbon from L-lysine source during the electroplating process were active toward the HER. Thus, to study more precisely the electrode activities, the EIS measurements were performed. A surface roughness factor (Rf) more than three orders of magnitude was obtained for the Ni81 P16 C3 electrode. The HER rate constants were estimated using Tafel-impedance data assuming the Volmer-Heyrovský path. Analysis of the Rf in conjunction with the values obtained for rate constantans showed that the increase in activity of the electrode was originated by 18% from increase in Rf and by 82% from increase in the intrinsic activity (synergetic effect). Microstructure and composition of the electrodes were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), and elemental microanalysis (EDX). Besides the good electrocatalytic activity, excellent chemical and electrochemical stability was observed for Ni81 P16 C3 composite electrode toward the HER. © 2008 International Association for Hydrogen Energy.
Journal of New Materials for Electrochemical Systems (14802422) 11(4)pp. 259-265
Nickel-phosphorus-codeposited graphite carbon (Ni-P-Cg) materials have been studied by means of electrochemical and mi-crostructural techniques. Steady-state polarization Tafel curves showed that the Ni-P-C electrodes were active toward the HER. The activity of the Ni-P-Cg materials was depended on the electrode composition and the best activity was obtained on Ni 83P12C5 electrode (n250 = -242.4±2.1 mV), which was subjected to annealing at 400 °C in argon atmosphere. EIS measurements revealed that the electrodes were active and the source of the activity was originated mainly from improvement in electronic structure of the catalyst, and partially from increase in the surface roughness caused by the heat treatment process mentioned above. Furthermore, the Volmer-HeyrovsĶý mechanism was determined for the HER and the latter was the rate-determining step. © J. New Mat. Electrochem. Systems.
Electroanalysis (15214109) 20(5)pp. 550-557
Functionalization of gold cysteamine (Au-CA) self-assembled monolayer with 4-formylphenylboronic acid (BA) via Schiff's base formation, through in situ method to fabricate Au-CA-BA electrode is presented and described. The fabricated electrode was used as a novel sensor for accumulation and determination of dopamine (DA). The accumulation of DA as a diol on the topside of Au-CA-BA as a Lewis acid, was performed via esterification (Au-CA-BA-DA), and followed for determination of DA. Functionalization, characterization, and determination steps were probed by electrochemical methods like cyclic voltammetry and electrochemical impedance spectroscopy. The data will be presented and discussed from which a new sensor for DA is introduced. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.
Electrochimica Acta (00134686) 53(22)pp. 6293-6303
A new, simple, and easy method for introducing hydroxamic acid group onto the surface of polycrystalline gold electrode by means of in-situ layer-by-layer functionalization is described. The fabrication was performed in a four-step method: (i) modification of gold by cysteamine self-assembled monolayer, Au-CA SAM, (ii) activation of nitrilotriacetic acid (NTA) by 1-ethyl-3(3- (dimethylamino)propyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS), (iii) immobilization of activated NTA onto Au-CA to form Au-CA-NTA, and (iv) conversion of the remaining activated carboxylic acid groups of Au-CA-NTA (terminals) to hydroxamic acid groups by using hydroxylamine hydrochloride (HAH) to form Au-CA-NDHA modified electrode. The resulting modified electrode was successfully tested for accumulation of zirconium ion (Zr(IV)) from an aqueous acidic solution. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were used to trace the events in each step, characterize the surface, determine the surface pKas, and find the affinity of the prepared electrode towards the Zr(IV). Surface pKas equal to 6.5 and 5.5 were estimated for Au-CA-NTA, and Au-CA-NDHA SAM electrodes, respectively. These values allowed estimating the charge-state of the surface at any pHs. The modified surface showed a large affinity for selective accumulation of Zr(IV) from acidic solution. © 2008 Elsevier Ltd. All rights reserved.
Sensors and Actuators B: Chemical (09254005) 137(1)pp. 195-204
Comparative electrochemical study of glucose oxidase (GOx) immobilized on gold electrodes modified by three types of mercaptocarboxylic acid self-assembled monolayers (SAMs), including 3-mercaptopropionic acid (MPA), 3-mercaptosuccinic acid (MSA), and thiodisuccinic acid (TDSA), is reported. GOx was immobilized on SAMs via anhydride route to prepare (Au-MPA-GOx), (Au-MSA-GOx), and (Au-TDSA-GOx) biosensors. Steps of formation and analytical performance of the prepared biosensors were traced by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). While partial surface coverage (θ) of gold by thiols showed the following order Au-MPA(θ = 36%) > Au-MSA(θ = 30%) > Au-TDSA(θ = 24%), inverse effect was observed for slopes (activities) of the calibration curves for glucose determination as Au-MPA-GOx < Au-MSA-GOx < Au-TDSA-GOx. This matter was explained based on advantages of multi-branch carboxylic acids (i.e. TDSA) allowing immobilization of more enzymes even with less surface coverage (24%) by thiols. Data obtained by CA and EIS methods for the entire of the study were in good agreement. © 2008 Elsevier B.V. All rights reserved.
Journal Of The Iranian Chemical Society (1735207X) 6(1)pp. 104-112
Application of immobilized metal cations on the topside of gold-5-amino-2-mercaptobenzimidazole self-assembled monolayer (Au-5A2MBI-Mn+ SAM, Mn+:Cu2+ or Ag+) for electrocatalytic determination of hydroquinone (H2Q) is described by voltammetric method. Several parameters were investigated to evaluate the performance of the sensors. Calibration curves for H2Q concentrations were linear from 1.0 × 10-5 to 4.0 × 10-4 M (r=0.998) for Au-5A2MBI, from 1.0 × 10-5 to 6.0 × 10-4 M (r=0.998) for Au-5A2MBI-Cu2+, and from 2.0 × 10-6 to 2.0 × 10-5 M (r=0.996) and 1.0 × 10-4 to 1.0 × 10-3 M (r=0.991) for Au-5A2MBI-Ag+ SAM modified electrode. The respective detection limits were found as 6.5 × 10-6, 4.6 × 10-6 and 1.8 × 10-7 M. Both Cu2+ and Ag+ ions were found to have a good electrocatalytic effect on the oxidation of H2Q; however, Ag+ was a more effective catalyst and showed better sensitivity and lower detection limit than all other tested electrodes. Au-5A2MBI-Ag+ SAM electrode was used as a suitable sensor for determination of H2Q in a radiolysis developing agent as real sample. The results obtained by using proposed sensor and that obtained by an ASTM reference method were in good agreement at the 95% confidence level.
Sensors and Actuators B: Chemical (09254005) 139(2)pp. 657-664
A new modified electrode is reported for the determination of zirconium ion (Zr(IV)) based on (i) in-situ functionalization of gold cysteamine self-assembled monolayer by nitrilotriacetic acid, and its further modification of by hydroxylamine hydrochloride as a recognition system, and (ii) electrochemical impedance spectroscopy (EIS) as a transduction method. Zr(IV) was selectively accumulated on the topside of hydroxameated surface, and the surface blocked the charge transfer process between metallic base and a redox probe in solution. The EIS complex plane plots showed a drastic change in the charge transfer resistance of the probe redox reaction as a function of Zr(IV) concentration. This behavior was used for construction of the calibration curve, and a linear range from 1.0 × 10-9 to 5.0 × 10-5 M Zr(IV) with a detection limit of 7.8 × 10-10 M and a relative standard deviation (RSD) of 1.79% for n = 5 at 5.0 × 10-5 M Zr(IV) was observed. The validity of the method and applicability of the sensor were successfully tested by determining Zr(IV) in synthetic as well as natural waters (tap and river waters) without interference from sample matrix. © 2009 Elsevier B.V. All rights reserved.
Bioelectrochemistry (15675394) 75(2)pp. 124-129
Immobilization of l-lysine α-oxidase on gold-mercaptopropionic acid self-assembled monolayer (Au-MPA-LOx SAM) electrode is verified experimentally in the present work. Fabrication steps and electrochemical interaction of Au-MPA-LOx with l-lysine were monitored by general electrochemical methods like cyclic voltammetry (CV) and chronoamperometry (CA), and by a more advanced method, electrochemical impedance spectroscopy (EIS) in the presence of parabenzoquinone (PBQ) redox probe. The data was analyzed from which quantitative kinetic parameters were extracted. The results confirmed successful immobilization of LOx, and thus, fabrication of Au-MPA-LOx SAM electrode. Our initial tests revealed a linear response for Au-MPA-LOx SAM electrode toward l-lysine concentration in solution at biological conditions, pH 7.4. The experimental data will be presented and discussed from which the Au-MPA-LOx SAM electrode is characterized, and the kinetic merits of the interface interactions are introduced. © 2009 Elsevier B.V. All rights reserved.
Journal of Electroanalytical Chemistry (15726657) 633(1)pp. 259-263
A new method is established for the electrochemical detection of zirconium ion (Zr(IV)) based on electrochemical impedance spectroscopy transduction method, and hydroxamated gold surface recognition system. The method successfully served for the detection of Zr(IV) with a wide dynamic range of 1.0 × 10-9 to 5.0 × 10-5 mol L-1, and a detection limit in nmol L-1 scale. Construction of the calibration curve by "one-impedance for one-concentration" method developed here helped us to save the experimental time by saving the data acquisition time by a factor of ∼20, and further, eliminating data approximation and parameter extraction times. © 2009 Elsevier B.V. All rights reserved.
Biosensors and Bioelectronics (18734235) 24(7)pp. 2199-2204
Preparation, characterization, and application of a new sensor for the determination of phosphate in blood serum is described by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and osteryoung square wave voltammetry (OSWV) in the presence of an appropriate redox reaction probe. The sensor was based on ionic adsorption of phosphate on Zr(IV) immobilized on gold-mercaptopropionic acid self-assembled monolayer (Au-MPA-Zr(IV) SAM) electrode. Parameters influencing the method were optimized. A linear range calibration curve from 1.0 × 10-7 to 1.0 × 10-6 M PO43- with a detection limit of 5.30 × 10-8 M and mean of relative standard deviations (R.S.D.) of 2.75% for n = 4 was observed in the best conditions by OSWV. Possible interferences from the coexisting ions were also investigated. The results demonstrated that sensor could be used for the determination of phosphate in the presence of various ions. Regeneration of the surface was carried out successfully by 5-min sonication in 0.1 M KOH solution and then 1-min incubation in 1.0 × 10-3 M Zr(IV) with a good reproducibility, R.S.D. = 1.47% for n = 4 by OSWV. The validity of the method and applicability of the sensor were successfully tested by detection of phosphate in blood serum after deproteinization of sample without interference from sample matrix. The long-term storage stability of the electrode was studied. The experimental data is presented and discussed from which the new sensor is characterized. © 2008 Elsevier B.V. All rights reserved.
Electroanalysis (15214109) 22(9)pp. 969-977
A new sensor, gold-6-amino-2-mercaptobenzothiazole (6A2MBT), was fabricated via a self-assembly procedure. Electrochemical properties of the monolayer were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The modified electrode showed excellent antifouling property against the oxidation products of DA, allowed us to construct a dynamic calibration curve with two linear parts, 1.00 10-6 to 3.72 10-4 and 3.72 10-4 to 6.42 10-4 M DA, with correlation coefficients of 0.997 and 0.992 and a detection limit of 1.57 10-7 M DA by using differential pulse voltammetry (DPV), respectively. Finally, the performance of the Au-6A2MBT modified electrode was successfully tested for electrochemical detection of DA in a pharmaceutical sample. © 2010 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim.
1 2 3
