Chronopotentiometric Determination Research Articles

Corrosion-assisted large-scale production of hierarchical iron rusts/Ni(OH)2 nanosheet-on-microsphere arrays for efficient electrocatalysis

Iron corrosion is always harmful to our industrial manufacture and thus numerous effects have been conducted for corrosion protection. However, the detrimental corrosion may be applied to produce serviceable materials, resulting in “upcycling waste into wealth”. Herein, a novel corrosion engineering is employed to fabricate hierarchical iron rusts/Ni(OH)2 nanosheet-on-microsphere arrays as effective oxygen evolution reaction (OER) electrocatalysts. Through physically mixing the fabricated ultrathin iron rusts with Ni(OH)2 microspheres, the as-prepared catalyst requires an overpotential of only 318 mV to achieve the current density of 20 mA cm−2. Besides, negligible increasement of overpotential is observed after continuous chronopotentiometric determination for 30 h. The excellent OER property is attributed to the formed oxygen bridges of Fe–O–Ni on the solid-solid contact sites, which promote oxidation of Ni2+ specieses via the interfacial Fe3+ of iron rusts (FeOOH). In particular, a large-scale production of 2.968 g iron rusts/Ni(OH)2 catalysts was successfully prepared by using this simple, lowcost yet valid corrosion engineering. This work provides a novel avenue towards large-scale production of efficient OER catalysts by combing with corrosion science, which is beneficial for boosting the progress of water splitting.

Current pulse based ion-selective electrodes for chronopotentiometric determination of calcium in seawater

Calcium is closely related to the oceanic biosphere and carbonate system. Potentiometry based on a calcium-selective electrode (Ca-ISE) represents a promising tool for detection of calcium ion activities in seawater. This technique, however, generally is limited by the low sensitivity for the inherent Nernstian response (i.e. ca 30 mV/dec). A current pulse based ion-selective electrode with enhanced sensitivity for chronopotentiometric measurements of calcium in seawater is proposed. The Ca2+-selective membrane containing lipophilic salt ETH 500 instead of traditional ion-exchanger is galvanostatically controlled. An applied constant cathodic current pulse can leads to the extraction of the calcium ions into the membrane to produce a chronopotential response, which shows a stable and reproducible super-Nernstian response in a narrow calcium activity range. The super-Nernstian region of the electrode depends on not only the the magnitude and duration of the applied current pulse but also the interfering ions. Under optimal conditions, the proposed Ca-ISE exhibits a super-Nernstian response between the calcium concentrations of 10−2.5–10−1.5 M with a slope of ca 80 mV/dec. The current pulse based Ca-ISE has been applied to determination of calcium in seawater with satisfactory results.

A comparison of different methods to remove dissolved oxygen: Application to the electrochemical determination of imidacloprid

This study compares different methods for the removal of oxygen from the solution prior to the chronopotentiometric determination of the insecticide imidacloprid on glassy carbon electrode. The research included the application of the chemical method involving addition of sulfite ion, and the physical method of purging the sample with nitrogen stream, as well as their combination. By comparing analytical signals of imidacloprid, chemical method showed almost the same efficiency as conventional physical method, while the best reproducibility was achieved by applying chemical method with addition of the saturated sodium sulfite solution. The method is very simple and can be applied for deoxygenation of the solution prior to the chronopotentiometric analysis. The application of the chemical deoxygenation significantly shortened duration of the chronopotentiometric analysis of imidacloprid from approximately 15 min to 1 min.

Solid-State Lead-Selective Electrodes- a New Insight into Measurements of Ions at Low Analyte Concentrations

In environmental analysis of ions, ion-selective electrodes (ISEs) are frequently investigated as candidates to improve already existing techniques. Potentiometric sensors have several advantages over other analytical techniques, e.g. portability, low energy consumption, and small size. This creates an opportunity to perform analysis at overall lower cost [1, 2]. Despite obvious advantages, ISEs due to the need of re-calibration and fouling are not yet implemented in environmental analysis of ions on an industrial scale [3, 4]. Vast majority or scientific reports dealing with measurements of ions in diluted samples are devoted to solid-contact and conventional (with inner filling solution) ISEs, however, the concept of lowering the detection limit was firstly introduced and studied with solid-state ISEs [5-8].In this study solid-state membrane electrodes were re-vitalized in measurements of ions at low analyte concentration in environmental samples. We used lead(II)-selective electrodes with PbS/Ag2S membranes to develop two methods lowering of the detection limit based on the concentration time-dependent adsorption of the primary ion on the surface of the membrane [9] and tuned galvanostatic polarization (chronopotentiometry) [10]. Furthermore, solid-state electrodes were used to determine lead concentration in environmental sample. Tuned galvanostatic polarization method was found suitable in measurement of lead(II) in environmental samples collected nearby industrially exposed terrain [11]. The chronopotentiometric determination was compared to the analysis done with inductively coupled plasma mass spectrometry (ICP-MS) and differential pulse anodic stripping voltammetry (DPASV). The tuned galvanostatic polarization method for the determination of lead in environmental sample was employed in our study for the very first time. By this application we open a new important direction for electrochemical measurement of ions at low analyte concentrations.

Catalytic Adsorptive Stripping Chronopotentiometric Determination of Hexavalent Chromium at a Silver Amalgam Film Electrode of Prolonged Application

AbstractThe paper reports on the application of stripping chronopotentiometry for the determination of chromium(VI) at a silver‐based amalgam film electrode. It is the first attempt to apply such a detection system for the speciation of chromium. The procedure utilized catalytic reduction of nitrate ions induced by the instantaneous chromium(III)‐DTPA complex, accumulated at the electrode surface. The chronopotentiometric step is realized in the constant current mode. Several key parameters, such as the deposition potential, deposition time, nitrate concentration and stripping current were optimized. The detection limit obtained for 15 s of accumulation time was estimated at 0.025 µg/L. The repeatability of the signal was 6.1 %.

Electrocatalytic Determination of Histamine on a Nickel‐Film Glassy Carbon Electrode

AbstractThe electrocatalysed oxidation of histamine on a thin film nickel electrode was investigated for the purpose of its chronopotentiometric determination. The oxidation mechanism implies complex and combined processes of histamine physical adsorption and consequent oxidation via joined oxidation potency of a constant current and electrochemically generated nickel‐oxihydroxide, which played a role of an electron transfer catalyst. Experimental parameters affecting the oxidation process, including type and concentration of supporting electrolyte, initial potential, oxidation current, temperature and concentration time, were optimised. Using a 240 s accumulation time, limit of detection and quantitation were 0.11 mg L−1 and 0.29 mg L−1 of histamine, respectively.

Determination of nickel in hair samples by graphite furnace atomic absorption spectrometry and flow-through stripping chronopotentiometry

Nickel in hair samples was determined by GF AAS and stripping chronopotentiometry after a dry ashing mineralisation with a mixture of nitrous oxides, oxygen and ozone. The use of common matrix modifiers brought no significant improvement in the GF AAS measurement. The detection limit, trueness and precision were found to be 0.15 mg kg−1 of the hair sample, 4.3%, and 4.1%, respectively. The linear range was found to be 0.44–3.3 mg kg−1. The stripping chronopotentiometric determination is based on the deposition of nickel ions from an ammonia buffer solution in a porous glassy carbon electrode followed by its stripping into an acidic solution by constant current. Copper interfered and was removed from the acidified sample solution by means of a minicolumn packed with pearl cellulose chemically modified with 8-hydroxychinolinol. Copper was trapped completely whereas nickel passed the column. The detection limit, trueness and precision were found to be 0.032 mg kg−1 in the hair sample, 5.8%, and 6.1%, respectively. The linear range was found to be 0.1–20 mg kg−1. Good agreement between the two methods was found for most hair samples.

Development of disposable bulk-modified screen-printed electrode based on bismuth oxide for stripping chronopotentiometric analysis of lead (II) and cadmium (II) in soil and water samples

A bulk-modified screen-printed carbon electrode characterised for metal ion detection is presented. Bismuth oxide (Bi 2O 3) was mixed with graphite-carbon ink to obtain the modified electrode. The best composition was 2% Bi 2O 3 (wt%) in the graphite-carbon ink. The modified electrode with onboard screen-printed carbon counter and silver–silver chloride pseudo-reference electrodes exhibited good performance in the electrochemical measurement of lead (II) and cadmium (II). The electrode displayed excellent linear behaviour in the concentration range examined (20–300 μg L −1) with limits of detection of 8 and 16 μg L −1 for both lead (II) and cadmium (II), respectively. The analytical utility of the modified electrode was illustrated by the stripping chronopotentiometric determinations of lead (II) in soil extracts and wastewater samples.

Cyclic chronopotentiometric determination of sugars at Au and Pt microelectrodes in flowing solutions

The main advantage of the application of cyclic chronopotentiometry (CCP) in end-column CE detection arises from the fact that the detection parameters and the magnitude of the analytical signal are (in contrast with other electrochemical detection methods) independent of the ohmic polarization of the solution caused by the separation current at the detection end of the capillary. CCP was used to determine sugars on platinum and gold microelectrodes after separation by CE. The results obtained with a gold microelectrode were better. Subsequently this detection method was used for quantitative determination of sugars in honeys and for their authentication.

Fast ultrasound-assisted treatment of urine samples for chronopotentiometric stripping determination of mercury at gold film electrodes

This work describes an efficient, fast, and reliable analytical methodology for mercury determination in urine samples using stripping chronopotentiometry at gold film electrodes. The samples were sonicated in the presence of concentrated HC1 and H 2O 2 for 15 min in order to disrupt the organic ligands and release the mercury. Thirty samples can be treated over the optimized region of the ultrasonic bath. This sample preparation was enough to allow the accurate stripping chronopotentiometric determination of mercury in the treated samples. No background currents and no passivation of the gold film electrode due to the sample matrix were verified. The samples were also analyzed by cold vapour atomic absorption spectrometry (CV-AAS) and good agreement between the results was verified. The analysis of NIST SRM 2670 (Toxic Metals in Freeze-Dried Urine) also validated the proposed electroanalytical method. Finally, this method was applied for mercury evaluation in urine of workers exposed to hospital waste incinerators.

Resolving the copper interference effect on the stripping chronopotentiometric response of lead(II) obtained at bismuth film screen-printed electrode

As copper(II) is a common ion in a variety of analytical samples, its effect on the stripping response of lead(II) at bismuth film screen-printed carbon electrode (BFSPCE) was investigated. The study was conducted using a screen-printed three-electrode system (working, counter and reference electrodes), with the carbon-working electrode plated in situ with bismuth film. Copper present at significant concentration level in samples was found to affect the sensitivity of the electrode by reducing the constant current stripping chronopotentiometric (CCSCP) response of lead(II). Recovery of the lead stripping response at the BFSPCE in the presence of copper was obtained when 0.1 mM ferricyanide was added to the test solution. The ferricyanide added circumvents the detrimental effect of copper(II) by selectively masking the copper ions by forming a complex. The analytical utility of the procedure is illustrated by the stripping chronopotentiometric determinations of lead(II) in soil extracts.

Stripping Chronopotentiometry with Dry‐Preservable Supporting Electrolyte

AbstractThe determination of some toxic metals by stripping chronopotentiometry with a supporting solution having an unconventional composition has been investigated with the aim of using such components in disposable measuring cells preservable in dry state and quite ready for use, only needing addition of a small volume of sample. The new supporting solution is prepared with a solid strong acid, p‐toluenesulfonic acid, in the place of the inorganic acids commonly used to improve the cation availability. The other components are, as usual, sodium chloride, which fixes the potential of the screen‐printed silver – silver chloride reference electrode, and mercury(II) chloride as the plating agent. This supporting solution has been tested in batch measurements with the mercury film glassy carbon electrode as well as with screen‐printed carbon‐ink electrodes, either with mercury film or bare. The physical shape of the mercury layer electrolytically deposited on screen‐printed carbon‐ink electrodes from a supporting solution containing 0.1 M p‐toluenesulfonic acid and 0.1 M sodium chloride has been investigated by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) microanalysis. In chronopotentiometric stripping p‐toluenesulfonic acid performs as well as the usual inorganic strong acids, particularly in terms of sensitivity. At 0.1 mol dm−3 it proved very suitable for the determination of toxic metals, in particular lead(II), at levels down to a few μg dm−3. The overall results appear promising and can open new avenues for preparing disposable cells for on‐field stripping chronopotentiometric determination of toxic metals.

Chronopotentiometric analysis of tocopherols using a glassy carbon vessel as the working electrode

Using a specific electrochemical cell with a glassy carbon vessel as the working electrode, a significant enhancement of the chronopotentiometric determination of tocopherols was achieved. Due to the large area of the working electrode, the method sensitivity was increased approximately 50-fold compared to the common electrochemical cell with a glassy-carbon disc electrode. Limits of quantitation of approximately 0.35 mg/dm 3 for α-, γ- and δ-tocopherol were obtained. The influence of the most important experimental factors was investigated and the method defined was applied for tocopherol determination in crude vegetable oils. The tocopherol content was determined by standard solutions prepared in a matrix of animal fat. An absolute method for γ- and δ-tocopherol quantitation is also described.

The discrete wavelet neural network and its application in oscillographic chronopotentiometric determination

The structure and algorithm of the discrete wavelet neural network (DWNN) are described. The network is constructed by the error back propagation neural network using Morlet mother wavelet basic function as node activation function. The effect of wavelet base number, learning rate factor and momentum factor on prediction are discussed. The experimental results of the quantitative computation for the concentration of mono-component and multi-component in oscillographic chronopotentiometric determination (OCPD) show that number of epochs is less than 1000, the recovery is between 94.37% and 104.3%. Compared with standard back propagation neural network, DWNN has higher convergence rate and prediction accuracy.

Molybdenum chemistry in molten LiCl–KCl eutectic: an electrochemical and absorption spectroscopy study of the concentration dependent stability of solutions of K 3MoCl 6

The chemical behaviour of LiCl–KCl–K 3MoCl 6 solutions between 400 and 500°C was investigated. They underwent slow decomposition, according to a concentration dependent disproportionation reaction yielding metallic molybdenum and a volatile black higher valency molybdenum compound, which corresponded with MoCl 5. Chronopotentiometric determinations showed a single 3-electron reduction, yielding Mo. The process was slow with diffusion-controlled mass transfer. The concentration of the Mo(III) species, presumed in the form of MoCl 6 3− ions, was determined using linear sweep voltametry and open circuit voltage measurements and the overall Mo(III) species concentration by chemical analysis. The results showed MoCl 6 3− to be the predominant species in the melt and the presence of a previously proposed dinuclear species, Mo 2Cl 9 3−, could not be confirmed electrochemically. This arose to quantification errors in the determination of the electroactive species MoCl 6 3− due to inherent problems in estimating the active surface area of the electrode. The electronic absorption spectrum of MoCl 6 3− in LiCl–KCl eutectic at 400°C is reported for the first time. Measurements were made above and below 0.045 mol dm −3 K 3MoCl 6, the concentration above which the disproportionation reaction was relatively slow. The results are discussed in detail and the spectroscopic parameters of the octahedral MoCl 6 3− complex were calculated as: Dq=1775 cm −1, B=511 cm −1 and C=1913 cm −1. Although an additional band, at 340 nm, appeared during disproportionation it could not be identified with any currently known polynuclear molybdenum chloro complex or oxychloro complex. It is probably associated with an intermediate in the disproportionation process. No spectral evidence was thus obtained in support of the formation of dinuclear molybdenum species.

Chronopotentiometric Determination of Aluminum by Solochrome Violet RS

A reliable and very sensitive derivative adsorption chronopotentiometric method for the determination of trace amounts of aluminum, based on the adsorptive accumulation of its solochrome violet RS complex on the HMDE, was developed in this paper. Experimental conditions were optimized including solution pH value, ionic strength, concentration of solochrome violet RS, preconcentration potential and preconcentration time. The linear working range was 0.27 ± 27 μg/1. The detection limit was 0.14 μg/1 and the relative standard deviation was 1.7% μg/1 Al. This method was applied to the determination of Al in real water samples. Comparison of the proposed method to the voltammetric mode and other ligands is presented.

Derivative adsorption chronopotentiometric determination of aluminum in natural and drinking waters using the AlIII‐1,2‐dihydroxyanthraquinone‐3‐sulfonic acid system

AbstractAn absorptive chronopotentiometric method was developed for the determination of trace aluminum. The method relies on the adsorptive accumulation of a AlIII‐1,2‐dihydroxyanthraquinone‐3‐sulfonic acid complex on the surface of a hanging mercury drop electrode. The optimum experimental conditions with respect to pH. preconcentration potential, preconcentration time and concentration of 1,2‐dihydroxyanthraquinone‐3‐sulfonic acid have been investigated. The suggested procedure has been used for the determination of aluminum in natural and drinking water samples and the accuracy investigated by comparison with results obtained by atomic absorption spectrometry.

Determination of trace adenine, adenosine and adenosine monophosphate by 2nd-order derivative adsorption chronopotentiometry

The characteristics of the derivative adsorption chronopotentiometric determination of adenine, adenosine and adenosine monophosphate (AMP) is discussed. The optimum experimental conditions for the determination of these compounds are selected and the linear ranges detected. The detection limits are 1.0 × 10 −9 mol l −1 for adenine, 1.5 × 10 −8 mol l −1 for adenosine and 4.6 × 10 −8 mol l −1 for AMP. The method was applied to determine the content of adenine in the hydrolytic product of yeast-RNA with satisfactory results.

Qualitative and quantitative chronopotentiometric determinations of Fe(II) species in molten silicates

Anodic chronopotentiometry is utilized to study the qualitative and quantitative behaviour of Fe(II) species in molten sodium disilicate glass at 950°C using a platinum wire working electrode and a reference electrode consisting of platinum/oxygen reference encased in yttria stabilized zirconia solid electrolyte. The iron content of the samples studied ranged 0–4 wt% as Fe 2O 3. Anodic chronopotentiograms of the Fe(II) containing glass melts exhibit a transition prior to platinum oxide/oxygen evolution with a quarter wave potential value of −0.309 V. The length of the transition time has been found to increase with the Fe(II) concentration. The iτ 1 2 values, which are constant at a given Fe(II) concentration, are shown to increase linearly with an increase in Fe(II) content. The diffusion coefficient of Fe(II) species has been calculated using the Sand equation and found to be (2.94±0.56) × 10 −7 cm 2 s −1.

Determination of thorium and scandium by indirect chronopotentiometric stripping analysis

A highly sensitive chronopotentiometric determination of thorium or of scandium is described. It is based on the substitution of thorium or scandium for lead (or zinc) in the lead—EDTA complex, and measurement of the liberated lead by deposition on a mercury film electrode, followed by a chemical oxidation stripping process during which the potential of the mercury electrode is monitored. Thorium has been determined at concentrations in the range 10 −5–10 −7 M by use of deposition times from 1 min to 1 hr.