Microband Sensor for As(III) Analysis: Reduced Matrix Interference

A portable sensor based on a microband design for arsenic detection in drinking water is presented. The work was focused to minimize interference encountered with a standard screen‐printed electrodes featuring an onboard gold working electrode, carbon counter and silver−silver chloride pseudo‐reference electrodes as composite coatings on plastic surface. The interference effect was identified as chloride ions interacting with the silver surface of the reference electrode and formation of soluble silver chloride complexes such as AgCl₄³⁻. By modification of the reference electrodes with Nafion membrane (5 % in alcohols), the interference was entirely eliminated. However, membrane coverage and uniformity can impact the electrodes reproducibility and performance. Hence, the sensor design was further considered and a microband format was produced lending favorable diffusive to capacitive current characteristics. Using the microband electrodes allowed As(III) detection with limit of detection of 0.8 ppb (in 4 M HCl electrolyte), inherently avoiding the problems of electrode fouling and maximizing analyte signal in river water samples. This is below the World Health Organization limit of 10 μg L⁻¹ (ppb). The electrolyte system was chosen so as to avoid problems from other common metal ions, most notably Cu(II). The presented electrode system is cost effective and offers a viable alternative to the colorimetric test kits presently employed for arsenic analysis in drinking water.     

Determination of Copper in the Presence of Various Amounts of Arsenic with L‐Cysteine Modified Gold Electrodes

An L ‐cysteine modified gold electrode for the determination of copper in the presence of various amounts of arsenic with anodic stripping voltammetry has been studied. The electrode was fabricated by immersing a gold electrode in an ethanol solution of 5mM L ‐cysteine for 60 min. Various parameters, such as the effect of different supporting electrolytes, the pH of the electrolyte and the deposition potential were investigated. Under optimum conditions, copper was accumulated at ?0.3 V (vs. SEC) for 60 s in 0.1 M phosphate buffer pH 5.0 in the presence of different amounts of arsenic. Essentially the same sensitivities (0.33±0.001 μA/μM) and limits of detection (0.13±0.002 μM) of copper were obtained with various amount of arsenic in the range 2 μM to 20 μM.     

Gold Nanoparticle Modified Electrodes Show a Reduced Interference by Cu(II) in the Detection of As(III) Using Anodic Stripping Voltammetry

Interference by Cu(II) causes serious problems in the detection of As(III) using anodic stripping voltammetry at gold electrodes. The behavior of Cu(II) and As(III) were examined at both a gold macro electrode and two kinds of gold nanoparticle modified electrodes, one where gold particles are deposited on glassy carbon (GC) and the other where basal plane pyrolytic graphite (BPPG) is the substrate. The sensitivity of As(III) detection was higher on gold nanoparticle modified electrodes than those on a macro gold electrode by up to an order of magnitude. In addition, the stripping peak of As(III) was narrower and more symmetric on a gold nanoparticle‐modified GC electrode, leading to analytical data with a lower limit of detection. At a macro gold electrode, the peak currents of Cu(II) were higher than those on gold nanoparticle modified electrodes. Accordingly, through the use of gold nanoparticle modified electrodes, the effect of copper interference to the arsenic detection can be reduced.     

As(III) Voltammetric Detection by Means of Disposable Screen‐Printed Gold Electrochemical Sensors

Abstract

In this paper a disposable gold screen‐printed working electrode was tested for arsenic detection in aqueous solutions using Square Wave Anodic Stripping Voltammetry (SWASV). The dynamic range of the sensor and its response were characterised in standard As(III) solutions; particular efforts were devoted to optimize electrode surface conditioning and electrolyte solution composition. The detection limit was 2.5 µg l^?1 using 60 s as deposition time. A portable battery‐operated device was used to demonstrate the possibility to use the sensor for on‐site analysis. Analysis of spiked samples was also performed.     

Hydrogen Evolution: Electrochemical Pretreatment for Voltammetric Analysis with Gold Electrodes

A pretreatment for gold electrodes is presented in this work. The improvement of the voltammetric responses for gold surfaces is achieved applying an adequate cathodic potential in acidic media which results on vigorous evolution of gas hydrogen at the interface between electrode and electrolyte. The effectiveness of this procedure is evidenced for gold wire electrodes by cyclic voltammetry in several redox systems. The pretreatment is also compared with other activation methods for gold electrodes in electroanalytical and electrochemical terms.     

Gold Nanoparticle Modified Screen Printed Electrodes for the Trace Sensing of Arsenic(III) in the Presence of Copper(II)

Gold ensembles for the trace level sensing of arsenic(III) in the presence of copper(II) are reported. The gold ensembles are fabricated using citrate capped gold nanoparticles which are chemically synthesised in an aqueous solution with an aliquot of this simply cast onto an economical and disposable screen printed electrode. After drying at room temperature, the gold ensembles are ready for use. The gold ensembles are explored towards the sensing of arsenic(III) in the presence of copper(II) using anodic stripping voltammetry where the corresponding stripping peaks are well resolved and using this protocol it is possible to readily detect 3 µg L^?1 (3 ppb) with a detection limit of 0.4 µg L^?1 (0.4 ppb). Proof‐of‐concept is also shown for the sensing of arsenic(III) in a canal water sample. Given the low cost of the sensor and ease of fabrication, the gold ensembles hold promise for the sensing of arsenic(III) in water samples where copper(II) may be present.     

Glassy Carbon Electrode Modified with Citrate Stabilized Gold Nanoparticles for Sensitive Arsenic (III) Detection

The electrochemical detection of As(III) was investigated on the novel citrate stabilized gold nanoparticle modified glassy carbon electrode (AuNPs/GCE) in 1 M HCl by square wave anodic stripping voltammetry. AuNPs/GCE was prepared by simply casting citrate stabilized gold nanoparticles onto the well-polished glassy carbon electrode. Gold modification was evaluated by cyclic voltammetry, while transmission electron microscopy and UV-vis Spectroscopy revealed the size and distribution of gold nanoparticles. Anodic stripping voltammetry was performed with the modified electrode in As(III) solution. Electrochemical experiments proved that AuNPS/GCE exhibited good performance for As(III) analysis, the linear range were obtained between 0.05 and 1 ppb for trace level of As(III) as well as 1 to 15 ppb, with a limit of detection of 0.025 ppb. In terms of reproducibility, the precision of the aforementioned method in %RSD was calculated at 7.78% (n = 10), and the repeatability of the proposed method was calculated to be 1.59%. The application of the method to analyze As(III) in tap water was investigated.     

Investigation into the voltammetric behaviour and detection of selenium(IV) at metal electrodes in diverse electrolyte media

The voltammetric behaviour of selenium(IV) was studied at platinum and gold electrodes in sulphuric acid, perchloric acid and potassium chloride media as a basis for its voltammetric detection. The best voltammetric behaviour was recorded at gold electrodes with perchloric acid as the supporting electrolyte. The concomitant presence of metals, such as copper or lead, and of model biomolecules, such as bovine serum albumin, in the solution resulted in a deterioration of the electrochemical response for selenium(IV). Quantitative detection of selenium(IV) by square wave anodic stripping voltammetry at both a millimetre-sized gold disc electrode and a microband electrode array revealed linear responses to selenium concentration in the ranges 5–15 μM and 0.1–10 μM, respectively, with 60 s preconcentration. The sensitivities were 6.4 μA μM⁻¹ cm⁻² and 100 μA μM⁻¹ cm⁻² at the disc and the microband array, respectively. The detection limit at the microband electrode array was 25 nM, illustrating the potentiality of such microelectrodes for the development of mercury-free analytical methods for the trace detection of selenium(IV).     

Trace analysis of cefotaxime at carbon paste electrode modified with novel Schiff base Zn(II) complex

Cefotaxime a third generation cephalosporin drug estimation in nanomolar concentration range is demonstrated for the first time in aqueous and human blood samples using novel Schiff base octahedral Zn(II) complex. The cefotaxime electrochemistry is studied over graphite paste and Zn(II) complex modified graphite paste capillary electrodes in H₂SO₄ (pH 2.3) using cyclic voltammetry and differential pulse voltammetry. Cefotaxime enrichment is observed over Zn(II) complex modified graphite paste electrode probably due to interaction of functional groups of cefotaxime with Zn(II) complex. Possible interactions between metal complex and cefotaxime drug is examined by UV-vis and electrochemical quartz crystal microbalance (EQCM) techniques and further supported by voltammetric analysis. Differential pulse voltammetry (DPV) with modified electrode is applied for the determination of cefotaxime in acidified aqueous and blood samples. Cefotaxime estimation is successfully demonstrated in the range of 1-500 nM for aqueous samples and 0.1-100 μM in human blood samples. Reproducibility, accuracy and repeatability of the method are checked by triplicate reading for large number of samples. The variation in the measurements is obtained less than 10% without any interference of electrolyte or blood constituents.     

Interference from Trace Copper in Electrochemical Investigations Employing Carboxylic Acid Terminated Thiol Modified Gold Electrodes

Unexpectedly, electrochemistry at variable chain length carboxylic acid terminated alkylthiol self‐assembled monolayers (SAMs) on gold electrodes gives rise to a Faradaic process in buffered aqueous electrolyte solution. In particular, the three‐carbon chain length, 3‐mercaptopropionic acid (MPA), exhibits a chemically reversible process with a mid‐point potential of 175 mV vs. Ag/AgCl under conditions of cyclic voltammetry. This process is associated with the presence of trace (parts per billion) amounts of copper(II) ions present in the chemical reagents used to prepare the aqueous electrolyte and also from the gold electrode itself. The carboxylic acid moiety on the SAM concentrates Cu²⁺ ions by coordination and this surface confined layer is then reduced. Methods to minimize the interference of Cu²⁺ ions at carboxylic acid terminated SAM are discussed and caution with respect to the interpretation of protein electrochemistry is recommended when using carboxylic acid functionalized SAMs to provide biocompatible electrochemical transduction surfaces, unless a metal free environment can be obtained.     

Anodic Stripping Voltammetry: Arsenic Determination in Ancient Bone Samples

Abstract

A highly sensitive method for the determination of arsenic (As) content in ancient bone samples was studied using a gold tipped rotating disc electrode and differential pulse anodic stripping voltammetry. Factors affecting sensitivity and precision, including electrolyte concentration, deposition potential, deposition time, and rotation rate were investigated. Electroinactive As(V) was reduced to As(III) by HCl 30% w/v prior to electroanalytical measurements. For a deposition time of 120 sec, the lowest detection limit (LOD) for arsenic was 1.078 µg/L. Optimized working conditions are defined as a deposition potential of ?1200 mV with a deposition time of 120 sec, 10 M HCl as the supporting electrolyte, and a rotation rate of 2000 rpm. Results of electroanalytial measurements in ancient bone samples are compared with those obtained from the hydride generation atomic absorption spectroscopy (HG‐FAAS) analysis. Analytical relevancy of the two methods was then compared with the aid of statistical data treatment.     

Preconcentration and Determination of Copper(II) at a Chemically Modified Electrode Containing Salicylaldehyde Thiosemicarbazone

A chemically modified electrode (CME) containing salicylaldehyde thiosemicarbazone (TSCsal) was evaluated for the ability to preconcentrate copper(II) prior to quantification by voltammetry. The CME has been used for the very sensitive and selective analysis of trace amounts of copper(II). A detection limit of 0.1 ppb was obtained by applying anodic stripping voltammetry with a flow system. The parameters that affect the sensitivity and possible interference by other ions or chelating agents have been examined in detail. The CME exhibits high stability and the response could be reproduced for four preconcentration-determination-renewal cycles [10ppbCu(II)] with a 2.87% relative standard deviation. The proposed method has been applied to the determination of copper(II) in tap water, drinking water, and NASS-3 standard reference sea water samples. The results gave satisfactory recoveries.     

溶出伏安法同时测定矿山地下水中痕量砷铅

本文以电化学预处理的金电极为工作电极,采用线性扫描溶出伏安法实现了矿山地下水中痕量As3+、Pb2+的同时测定。研究了金电极的预处理方法、不同预富集时间和不同电解质对重金属离子测定的影响规律。研究发现,电化学预处理有利于金电极对重金属离子的响应,在最优实验条件下,As3+、Pb2+在电化学活化的金电极上分别于0.18V、-0.07V产生灵敏的溶出峰,峰高与其浓度线性相关,检测限分别可达到0.5!g/L、2!g/L。该方法操作简单、干扰小、线性范围宽、灵敏度高。     

Sensitive Determination of Trace Pb2+ in Seawater Using Columnar Glassy Carbon Electrode

We herein report a mercury‐free approach for the sensitive determination of trace Pb²⁺ in seawater using differential pulse stripping voltammetric (DPSV) method with a novel columnar glassy carbon electrode (CGCE). Compared with the conventional disk glassy carbon electrode with the same diameter, it has much larger electrochemical area (0.627 ± 0.003 cm²). The CGCE shows good accumulation ability and consequently acceptable behavior which makes it suitable as a working electrode in the DPSV determination of Pb2+ with the great advantage of the avoidance of harmful mercury. Using acidified artificial seawater as supporting electrolyte, there was a good linear relationship between the peak currents and the concentration of Pb²⁺ in the range of 0.6～140.0 μg L^‐1 with a detection limit of 0.3 μg/L (S/N = 3) when the accumulation time was 300 s. The method was employed to determine trace levels of Pb²⁺ in real seawater samples successfully.     

The Suitability of Various Electrode Materials for the Electrogeneration of Halogens in Constant-Current Coulometry

Abstract

During a voltammetric study of the suitability of platinum, gold, glassy carbon, tungsten, and tantalum as electrode materials for generating halogens in constant-current coulometry it was found that glassy carbon, tungsten, and tantalum are not suitable. Both platinum and gold electrodes can be used; with platinum the possibility of interference caused by formation of complexes of the electrode metal with halides is smaller than with gold.     

Stripping Analysis of Trace Arsenic Based on the MnOx/AuNPs Composite Film Modified Electrode in Alkaline Media

A simple, rapid fabricated and sensitive modified electrode for detection of As(III) in alkaline media was proposed. The modified electrode was prepared by co‐electrodeposition of manganese oxides (MnO_x) and gold nanoparticles (AuNPs) on the glassy carbon electrode (GCE) with cyclic voltammetry. Linear sweep anodic stripping voltammetry (LS‐ASV) was employed for the determination of arsenic (III) without interference from Cu(II), Hg(II), and other coexisting metal ions. A lower detection limit of 0.057 µg L^?1 (S/N=3) were obtained with a accumulation time of 200 s. The proposed method was successfully applied to determine arsenic (III) in real water samples with satisfactory recoveries.     

Cold Deposition as a Novel Procedure for the Preparation of Titania Sol‐Gel: A Development of a High Sensitive Electrochemical Method for Determination of Cu(II) in the Presence of Arsenic(III)

Titania sol‐gel modified gold electrode (TSGMGE) was prepared with the usage of a new proposed cold deposition method at ?10 °C. Scanning electron microscope (SEM) operating at 30 kV was used to obtain micrographs of unmodified and modified electrodes. The obtained results showed that this procedure yields a sol‐gel with high porosity in comparison to conventional methods. The modified Au electrode was fabricated by trapping the L‐glutamine in titania sol‐gel at low temperatures to preparation of a new titania sol‐gel glutamine modified gold electrode (TSGGMGE). The possibility determination of traces of Cu(II) in the presence of As(III) was investigated using proposed electrode. Under the optimized conditions, copper was accumulated at ?0.35 V (vs. Ag/AgCl) for 40 s in 0.1 M acetate buffer (pH 4.0) in the presence of different amounts of arsenic. Two dynamic linear responses with good reproducibility were observed for copper ions in the concentration range of 1 × 10^?6 ?4 × 10^?4 M and 4 × 10^?8 ?6 × 10^?7 M.     

Application of gallium film electrode for elimination of copper interference in anodic stripping voltammetry of zinc

For elimination of copper interference in anodic stripping determinations of zinc at mercury and bismuth film electrodes gallium ions are usually added to the supporting electrolyte. In the presented studies novel ex situ formed gallium film electrode was applied for this purpose. The proposed electrode is less toxic than mercury one while the detection limit for zinc was lower than for bismuth film electrode following the same deposition time. The calibration graph for deposition time of 60 s was linear from 5 × 10⁻⁸ to 2 × 10⁻⁶ mol L⁻¹. The determinations of zinc were carried out from undeaerated solutions. The proposed procedure was applied to zinc determination in certified reference material and tap water sample.     

Detection of As(III) via oxidation to As(V) using platinum nanoparticle modified glassy carbon electrodes: arsenic detection without interference from copper

The electrochemical detection of As(III) was investigated on a platinum nanoparticle modified glassy carbon electrode in 1 M aqueous HClO4. Platinum nanoparticle modified glassy carbon electrodes were prepared by potential cycling in 0.1 M aqueous KCl containing 1 mM K2PtCl6. In each potential cycle, the potential was held at + 0.5 V for 0.01 s and at -0.7 V for 10 s. 25 cycles were optimally used to prepare the electrodes. The resulting electrode surfaces were characterized with AFM. The response to arsenic(III) on the modified electrode was examined using cyclic voltammetry and linear sweep voltammetry. By using the As(III) oxidation peak for the analytical determination, there is no interference from Cu(II) if present in contrast to the other metal surfaces (especially gold) typically used for the detection of arsenic; Cu(II) precludes the use of the As(0) to As(III) peak for quantitative anodic stripping voltammetry measurements due to the formation of Cu3As2 and an overlapping interference peak from the stripping of Cu(0). After optimization, a LOD of 2.1 +/- 0.05 ppb was obtained using the direct oxidation of As(III) to As(V), while the World Health Organization's guideline value of arsenic for drinking water is 10 ppb, suggesting the method may have practical utility.