Wave Adsorptive Stripping Voltammetry Research Articles

Nanoengineered electrochemical sensor based on mesoporous silica thin-film functionalized with thiol-terminated monolayer

A mesoporous silica thin film was synthesized via a surfactant-templating process, where a silica sol gel is spin-coated onto the surface of a microchip-based gold microelectrode. Within the film was a cubic lattice of pores having a primary size of 77 A. Thiol (-SH) functional groups were subsequently immobilized onto the mesoporous silica thin film through a self-assembly process. The thiol-functionalized mesoporous silica (SH-FMS) thin film was used as the electrode sensing layer for detection of lead(II) in aqueous solutions by employing a square wave adsorptive stripping voltammetry technique. The electrode modified with the SH-FMS thin-film utilized the binding affinity of lead(II) to the thiol ligands to perform the preconcentration step under an open circuit, with no additional electrolytes. The voltammetric responses for lead(II) increased linearly with the preconcentration time from 1 to 30 min. The responses also increased linearly with lead(II) concentrations ranging from 250 to 5000 ppb after 5 min preconcentration and from 25–100 ppb after 30 min preconcentration.

Determination of nifedipine in human plasma by square wave adsorptive stripping voltammetry

A simple, sensitive and selective square-wave adsorptive stripping voltammetric method has been developed and validated for the determination of nifedipine (NIF) in plasma. The assay was performed after single extraction of NIF from alkalinised plasma into organic phase. The adsorption behaviour of NIF on a hanging mercury drop electrode (HMDE) was explored by square-wave and cyclic voltammetry. The drug was accumulated at HMDE and a well-defined peak was obtained at −730 mV versus Ag/AgCl in borate buffer of pH 9.0 including 0.01 M KCl. The linear concentration range was 2.89×10 −9 M–3.61×10 −7 M (1.00–125.01 ng ml −1) when using 30 s accumulation time at −300 mV. Limit of detection and limit of quantification were 1.21×10 −9 M (0.42 ng ml −1) and 2.89×10 −9 M (1.00 ng ml −1) respectively. The intra-day relative standard deviation (RSD) ranged from 1.93 to 4.12% at three concentrations and the inter-day RSDs varied from 2.53 to 6.68%. The method was applied, to the plasma of pregnant women suffering from pregnancy induced hypertension, for the determination of NIF. The percentage recoveries varied from 96.26 to 99.49%. It has been shown that NIF could be determined in the presence of its main metabolite (dehydronifedipine) by the developed method.

Determination of ketorolac in human serum by square wave adsorptive stripping voltammetry

The adsorption behavior of ketorolac on a hanging mercury drop electrode (HMDE) was explored by square-wave and cyclic voltammetry. The square wave voltammetric response of ketorolac depends on the parameters of the square wave voltammetry excitation signal as well as on the pH of the medium and the accumulation time. The drug was accumulated at HMDE and a well-defined peak was obtained at −1.41 V versus. Ag/AgCl (saturated KCl) in acetate buffer of pH 5.0. A square-wave adsorptive stripping voltammetric method for the quantitative determination of ketorolac was developed. The linear concentration range was 1×10 -10–1×10 −8 when using 300 s accumulation at −0.8 V. The detection limit of ketorolac was 1.0×10 -11 M . The precision was excellent with relative standard deviation of 3.85% at concentration of 5×10 −8 M after 60 s accumulation time. Applicability to serum samples was illustrated. A detection limit of 14 ng per ml of serum was obtained.

SQUARE WAVE STRIPPING VOLTAMMETRY OF TITANIUM BASED ON ADSORPTIVE ACCUMULATION OF ITS HYDROXYNAPHTHOL BLUE (HNB) COMPLEX AT THE STATIC MERCURY DROP ELECTRODE

A new method is described for the determination of titanium based on the square wave adsorptive stripping voltammetry of Ti(IV) complexed with Hydroxynaphthol blue (HNB) at the static mercury drop electrode. Optimal conditions were found to be: preconcentration potential, −0.140 V vs. Ag/AgCl (KCl 3M); preconcentration time, 30 s (with stirring solution); pulse height, 75 mV;frequency, 100 Hz; scan increment, 4 mV; step time, 0.010 s; supporting electrolyte, acetate buffer (0.1 M, pH 3.2), and concentration of hydroxynaphthol blue, 1.0 × 10−5 M. The response of the system was found to be linear in a range of Ti(IV) concentrations from 5.0 to 20.0 μg/L. The limit of detection was found to be 0.18 μg/L and the limit of determination to be 1.09 μg/L, both using 30 s of preconcentration time. The effects of various potential interferences were also studied including a variety of cations, anions, and organic surfactants. The merits of the procedure were demonstrated in the analysis of certified NIST SRM 1633b and 1646a samples.

Study and determination of the pesticide Imidacloprid by square wave adsorptive stripping voltammetry

An electroanalytical method has been developed for the detection and determination of the pesticide 1-(6-chloro-3-pyridylmethyl)- N-nitroimidazolidin-2ylidineamine (Imidacloprid) by square wave adsorptive stripping voltammetry on a hanging mercury drop electrode (HMDE) in aqueous solution with Britton–Robinson buffer as supporting electrolyte. The best adsorption conditions were found to be pH 7.2, an accumulation potential of −1050 mV (HMDE vs. Ag/AgCl–KCl 3M) and an accumulation time of 50 s. Effects of square wave frequency, step potential and pulse amplitude were examined for the optimization of instrumental conditions. Calibration curve is linear in the range 2×10 −8–5×10 −7 M with a detection limit of 1.6×10 −8 M (Clayton et al. method). The method is applied to the direct determination of the pesticide in river water samples. For a concentration of 4.1×10 −8 M a recovery value of 104±3% is obtained. In order to determine lower concentrations, previous preconcentration and cleaning steps (liquid–liquid extraction into CH 2Cl 2 and solid-phase extraction with Sep-Pak C 18 cartridges) are carried out. The recovery values obtained in spiked river water are 89±4% for 2×10 −8 M and 90±6% for 8×10 −9 M.

Square wave Stripping voltammetry of Cobalt Based on Adsorptive accumulation of its Hydroxynaphthol Blue (HNB) Complex at the Static Mercury Drop Electrode

ABSTRACT A new method is described for the determination of cobalt based on the square wave adsorptive stripping voltammetry of Co(II) complexed with hydroxynaphthol blue (HNB) at the static mercury drop electrode. Optimal conditions were found to be: preconcentration potential, -0.500V vs. Ag/AgCl (KCl 3M); preconcentration time, 30 s (with stirring); pulse height, 50 mV; frequency, 100 Hz; scan increment, 4 mV; step time, 0.010 s; supporting electrolyte, HEPES/HCl (0.1 M, pH 7.0-8.0) or triethanolamine/HCl (0.1 M, pH 7.6); concentration of hydroxynaphthol blue, 5.0 × 10−6 M. The response of the system was found to be linear in a range of Co(II) concentrations from 2.0 to 10.0 μg/L. The limit of detection was found to be 1.8 × 10−9 M with 2 minutes of preconcentration time. The effect of various potential interferences were also studied including a variety of cations, anions and organic surfactants. The interferences by Ni(II), and Cr(VI) may be eliminated by addition of EDTA or CDTA and the of Fe(III) and Ti(IV) by fluoride. The merits of the procedure were demonstrated in the analysis of certified and biological samples.

Optimization of the experimental parameters in the determination of rifamycin SV by adsorptive stripping voltammetry

A procedure for the determination of rifamycin SV by adsorptive stripping voltammetry (AdSV) has been optimized. Two different voltammetric techniques, namely differential pulse adsorptive stripping voltammetry (DPAdSV) and square wave adsorptive stripping voltammetry (SWAdSV) were used. In order to determine the most sensitive technique, an optimization of the experimental parameters was carried out for every technique using experimental design methodology. A canonical analysis of the response surface was carried out, which was adjusted to determine the optimum and the influence of the experimental factors. When this lay outside the ambit of the experiment, the optimum path method was used for the optimising process. The detection limits obtained, 3.108 × 10 −8 mol dm −3 for DPAdSV and 1.233 × 10 −8 mol dm −3 for SWAdSV, show that SWAdSV is a more sensitive technique for the analysis of rifamycin SV. Finally, this method was used to determine rifamycin SV in real samples.

Determination of salmon calcitonin by square wave adsorptive stripping voltammetry

Salmon calcitonin (SC) was characterized voltammetrically at a mercury electrode by means of cyclic and square wave voltammetry. The voltammetric behavior of SC resembles the voltammetry of other biologically active compounds containing disulfide group(s). The existence of a well shaped peak due to reduction of adsorption SC was exploited to yield a sensitive analytical method for determination of SC concentration. Square wave adsorptive stripping voltammetry allows determination of SC at nanomolar levels.

Square wave adsorptive voltammetric determination of sunset yellow

Square wave adsorptive stripping voltammetry was used for determining trace amounts of dye Sunset Yellow (E-110) for the first time. Its adsorptive voltammetric behaviour followed by a square wave mode step was investigated at different pH media. Sunset Yellow in 0.5 M NH 4 Cl NH 3 buffer solution gave an adsorptive stripping voltammetric peak at the hanging mercury drop electrode at −0.60 V using an accumulation potential of −0.40 V. The effect of experimental parameters that affected this determination are discussed. The calibration graph to determine Sunset Yellow was linear in the range 5–90 μg 1 −1, obtaining a relative standard deviation of 2.2% for a solution of 30 μg 1 −1 ( n = 10) in the same day. The determination limit was 5 μg 1 −1 after 15 s of accumulation at −0.40 V. The proposed method was applied to determine this dye in several commercial refreshing drinks, which contained small amounts of this compound. Measurements were made directly over diluted solutions of commercial samples. Similar results were obtained between adsorptive stripping square-wave voltammetric values and the obtained by application of a HPLC method with spectrophotometric detection.

Square wave adsorptive stripping voltammetry of nickel(II) in flowing systems at a wall‐jet mercury film electrode plated in situ

AbstractA rapid and highly sensitive adsorptive stripping voltammetry method for the measurement of traces of nickel(II) in flowing systems is described. The method involves a mass‐transport controlled preconcentration step, during which the NiII‐dimethylglyoxime complex is adsorbed onto an in situ plated mercury film wall‐jet electrode, followed by a reductive square wave stripping scan. The optimization of the experimental conditions and square wave parameters was carried out in order to achieve high sensitivity, reproducibility and fast response. The detection limit, restricted by the amount of nickel in the blank solution, was found to be 1.3 × 10−10 M, with a relative standard deviation of ±12.2% (n = 15), for a 1‐min accumulation time. Linear calibration plots were obtained up to 8 × 10−10 M. This method can be applied to continuous on‐line monitoring of trace levels of nickel in flowing systems, enabling easy automation.

Square wave adsorptive stripping voltammetry of nickel and cobalt at wall‐jet electrodes in continuous flow

AbstractSquare wave adsorptive stripping voltammetry (SWAdSV) of nickel and cobalt at wall‐jet electrodes in a continuous flow system has been evaluated. Characteristics and advantages relative to differential pulse adsorptive stripping voltammetry (DPAdSV) in continuous flow systems are explored. Under optimized experimental conditions, sensitivity is approximately a factor of ten higher than DPAdSV, and one‐nanomolar detection limits are achieved. Solution deoxygenation is unnecessary and sample throughput is increased.

Batch injection analysis with adsorptive stripping voltammetry for the determination of traces of nickel and cobalt

AbstractSquare wave adsorptive stripping voltammetry (AdSV) in conjunction with the batch injection analysis technique has been investigated at mercury thin‐film electrodes, using analysis of nickel and cobalt ions with nioxime ligand as example, and injection of sample volumes of ≤100μL. Experiments were conducted in a HEPES neutral buffered medium, suitable for analysis of biological fluids. Sensitivity is maximized by continuing the adsorptive accumulation after the end of the injection period, and employing the lowest possible injection rate from the electronic micropipette of 24.5μLs−1. The practical detection limit is 5 nM for nickel and 2 nM for cobalt. Comparison is made with batch injection analysis with anodic stripping voltammetry and the merits of the technique relative to continuous flow‐through methods are assessed.

Application of an optimization procedure in adsorptive stripping voltammetry to the determination of nickel with DMG

AbstractA procedure for the determination of nickel by adsorptive stripping voltammetry (AdSV), using dimethylglyoxime as complexing agent, has been optimized. The determination was carried out by two different techniques: differential pulse adsorptive stripping voltammetry (DPAdSV) and square wave adsorptive stripping voltammetry (SWAdSV). The selection of the experimental parameters was done using a factorial design which allows one to find the most significant variables, i.e., those which exert the greatest influence on the measured magnitude, with a reduced number of experiments. Posterior optimization of these variables provided the most adequate experimental conditions and it was under these conditions that the calibrations were made, using a robust regression method which allows the elimination of anomalous points.

A study of riboflavin determination by square wave adsorptive stripping voltammetry on mercury film electrodes

AbstractIn this work riboflavin was determined by square wave adsorptive stripping voltammetry (SWASV): riboflavin was initially adsorbed on a mercury film electrode (MFE) at a potential of 0.0 V (vs. Ag/AgCl) and at pH 12; the subsequent reductive stripping step was carried out by applying a square wave potential‐time waveform on the electrode. Both a batch method (based on the rotating disk electrode configuration) and a flow approach [based on the wall‐jet flow‐through electrode and flow injection analysis (FIA)] were employed. Both instrumental and chemical parameters were investigated and optimized for analytical use of the technique. The limit of detection was 0.5 nmol L −1 (for 10 min of preconcentration), the precision was 8% for the batch system (at the 10 nmol L−1 level) and 6% for the flow system (at the 100 nmol L−1 level); the linear range depended on the preconcentration time and the mass transfer conditions during the accumulation step. Both methods were automated and applied to the determination of riboflavin in commercial pharmaceutical products with recovery values at over 90%.

Square wave adsorptive stripping voltammetry of molybdenum(VI) in continuous flow at a wall-jet mercury film electrode sensor

An adsorptive stripping voltammetry method for the determination of traces of molybdenum(VI) in flowing solution at a wall-jet electrode sensor has been developed. After adsorption of a molybdenum complex on a wall-jet mercury film electrode, the complex is reduced by a square wave scan. More satisfactory results were obtained using 8-hydroxyquinoline as a complexing agent in nitrate medium than using Toluidine Blue in oxalic acid. Enhanced sensitivity was achieved by optimizing adsorption time and square wave parameter values. The detection limit of Mo(VI) was found to be at the nanomolar level. Interference of some other metallic species in the determination of nanomolar Mo(VI) was also investigated: Cu(II), Zn(II), Mn(II) do not interfere at 10 μ M, whereas 1 μ M FeEDTA − causes an increase in peak current. This iron interference was removed effectively with citric acid.

Batch and flow determination of uranium (VI) by adsorptive stripping voltammetry on mercury-film electrodes

Uranium(VI) was determined by square wave adsorptive stripping voltammetry on a rotating-disc mercury-film electrode using 8-hdyroxyquinoline as a complexing agent (batch mode), or, alternatively, on a wall jet mercury-film electrode with cupferron as complexing agent (flow-through mode). For the flow-through configuration, the combination of a novel wall jet cell with an automated flow system and a commercial computer-controlled potentiostat allowed complete keyboard control of the sequence of operations. Both continuous flow and flow injection (FI) schemes for preconcentration were assessed, and various instrumental parameters are discussed. Linearity held typically for a concentration range of two orders of magnitude (for 60 s preconcentration). It was found that, whereas the batch and continuous-flow modes are more suitable for the determination of lower concentrations of UVI( 10–7 mol l–1). The batch and flow methods were, finally, applied to the determination of UVI in a reference sea-water sample with accuracies of 7.2 and 4.2%, respectively, and relative standard deviations of 7.8 and 8.3%, respectively.

Square wave adsorptive stripping voltammetry on mercury film electrodes

In this paper the relative advantages of using square wave adsorptive stripping voltammetry in combination with a mercury film electrode as the working electrode were assessed. It was found that the resulting technique is fast, sensitive, offers excellent discrimination against the background current and can be used without deoxygenation of the sample; the analytical applications of the technique are demonstrated for the determination of Ni(II) with a limit of detection of 0.85 nmol 1−1 and a linear range of 3 orders of magnitude (for 60 s preconcentration) and for the determination of Cu(II) in the nmol 1−1 concentration level in the presence of dissolved oxygen.

Application of ultra-high vacuum technique to the study of surface chemistry and friction

This work reports the fabrication of disposable three-electrode cells with integrated sputtered metal-film electrodes. The working electrode was a bismuth-film electrode (BiFE) while the reference and counter electrodes were made of Ag and Pt, respectively. The deposition of the metal layers was carried out by sputtering of the respective metals on a silicon substrate while the exact geometry of the electrodes was defined via a metal mask placed on the substrate during the deposition process. Initially, the electrodes were characterised by cyclic voltammetry. The utility of these devices was tested for the trace determination of Ni(II) by square wave adsorptive stripping voltammetry (SWAdSV) after complexation with dimethylglyoxime (DMG). The experimental variables (the presence of oxygen, the DMG concentration, the preconcentration potential, the accumulation time and the SW parameters), as well as potential interferences, were investigated. Using the selected conditions, the 3σ limit of detection was 100 ng L−1 for Ni(II) (for 90 s of preconcentration) and the relative standard deviation for Ni(II) was 2.3% at the 10 μg L−1 level (n = 8). Finally, the method was applied to the determination of Ni(II) in a certified river water sample.