Square-wave Adsorptive Stripping Voltammetry Research Articles

Novel Application of Square-Wave Adsorptive-Stripping Voltammetry for the Determination of Xanthohumol in Spent Hops

This paper reports the development of a novel electrochemical assay for xanthohumol (XN) by square-wave adsorptive-stripping voltammetry (SWAdSV) with a hanging mercury drop electrode. The method showed good repeatability (CV < 2%) and linearity (between 10 and 250 μg L(-1)), as well as suitable limits of detection (2.6 μg L(-1)) and quantification (8.8 μg L(-1)). The method was applied for the quantification of this compound in spent hops, and the results obtained were compared with the HPLC-UV method. XN contents determined by the SWAdSV method were 16 ± 1 and 100 ± 4 μg L(-1) for aqueous and methanolic extracts, respectively. The developed new methodology considerably reduces the analysis time, approximately from 25 min (HPLC-UV method) to 7 min, enabling a high sample throughput. In addition, the detection and quantification limits were approximately 5-fold lower than those obtained with the chromatographic method.

Application of Catalytic Hydrogen Evolution in the Presence of Neonicotinoid Insecticide Clothianidin

Clothianidin, a new generation of pesticide, was determined in spiked tap water, apple juice, and soil by square-wave adsorptive stripping voltammetry. The method of determination is based on the hydrogen evolution reaction catalyzed by clothianidin at the hanging mercury drop electrode. The optimal signal was detected at −1.4 V versus Ag/AgCl in citrate buffer at pH 2.2. Various parameters such as pH, buffer concentration, frequency, amplitude, step potential, accumulation time, and potential were investigated to enhance the sensitivity of the determination. The optimal results were recorded at an accumulation potential of −0.35 V, accumulation time of 7 s, amplitude of 100 mV, frequency of 200 Hz, and step potential of 7 mV. The mechanism of catalytic hydrogen evolution was considered under experimental and theoretical conditions. This electroanalytical procedure enabled to determine clothianidin in the concentration range 9 × 10−9–4 × 10−6 mol L−1 in supporting electrolyte and tap water, 1 × 10−7–4 × 10−6 mol L−1 in diluted apple juice, and 2 × 10−7–1 × 10−6 mol L−1 in soil. The detection and quantification limits in supporting electrolyte and diluted apple juice were found to be 2.6 × 10−9, 8.6 × 10−9 and 3 × 10−8, and 1 × 10−7 mol L−1, respectively. A standard addition method was successfully used to determine clothianidin in spiked tap water, spiked apple juice, and spiked soil.

Electrochemical behaviour of tilmicosin at the hanging mercury drop electrode

The electrochemical behaviour of tilmicosin (TIM) was investigated using cyclic voltammetry and square-wave voltammetry in Britton-Robinson buffers (pH 2–12). The voltammograms of TIM showed one-irreversible peak which attributed to reduction of the >C=C C=C C=C< group was shifted to the more negative values with increasing pH. According to the obtained voltammetric data, the probable reaction mechanism for the reduction of TIM was proposed. Moreover, the adsorption of TIM on the mercury electrode surface by means of square-wave adsorptive stripping voltammetry measurements is studied at different pH values. The peak current variations with the deposition time and TIM concentration were observed.

Adsorptive stripping voltammetric methods for determination of ezetimibe in tablets

In this study, square-wave adsorptive stripping voltammetry (SWAdSV) and differential pulse adsorptive stripping voltammetry (DPAdSV) were used for determination of ezetimibe (EZE) in the presence of 0.1 m K2HPO4–Na2B4O7 (1:1) supporting electrolyte. The well-defined peaks for SWAdSV were observed at accumulation time of 15 s, accumulation potential of -0.80 V, frequency of 15 Hz, pulse amplitude of 25 mV, potential increment of 4 mV. For DPAdSV, accumulation time of 15 s, accumulation potential of -0.85 mV, scan rate of 20 mV/s and pulse amplitude of 50 mV were found as the best apparatus parameters. EZE gave rise to a single voltammetric peak in the potential interval from -1236 to -1252 mV for SWAdSV and interval from -1190 to -1210 mV for DPAdSV. The developed methods were validated according to the ICH guideline and were found to be linear, sensitive, specific, precise and accurate. The linearity ranges of EZE for SWAdSV and DPAdSV are 33–596 ng/ml and 66–400 ng/ml, respectively. The developed method was applied successfully for the determination of EZE in tablet dosage form.

Electrocatalytic Application of Girard's Reagent T to Simultaneous Determination of Furaldehydes in Pharmaceutical and Food Matrices by Highly Sensitive Voltammetric Methods

AbstractSensitive and precise voltammetric methods for the determination of trace amounts of furaldehydes, mainly as furfural (F) and 5‐hydroxymethyl‐2‐furaldehyde (HMF), in foods, pharmaceutical and other matrices is described. Determination of total furaldehyde at &lt;μg g−1 levels in alkaline buffered aqueous media was individually investigated. By the use of ordinary SWV and adsorptive square wave stripping voltammetry (Ad‐SWSV), the detection limits for determination of F and HMF found to be 400 and 10 ng g−1, respectively. At a 1.0 μg g−1 level of furfural in sample, the relative standard deviation (n=4) was 2.79%. The application of Ad‐SWSV to the determination of F and HMF, after their in situ derivatization with trimethylaminoacetohydrazide chloride (Girard's reagent T) at a static mercury drop electrode (SMDE) in NH3‐NH4Cl buffer of pH 9.5, resulted in a limit of detection of 10 ng g−1 for the resolved peaks of HMF and F. The results obtained by the proposed method for the real samples were compared with the corresponding results from UV‐spectrophotometry and HPLC experiments in various matrices.

Determination of trans-resveratrol in red wine by adsorptive stripping square-wave voltammetry with medium exchange

In the present paper, a method for the determination of trans-resveratrol in red wine samples, by adsorptive stripping square-wave voltammetry (Ad-SSWV) in a glassy carbon electrode, is presented. In 0.10 M perchloric medium, trans-resveratrol experiments an adsorptive–oxidative process, which promotes the appearance of a peak at 0.72 V. Calibration graph have been constructed from 5.0 to 35 ng/mL. Detection limit of 4.2 ng/mL has been calculated, according to Clayton criterion. Extraction of trans-resveratrol from red wine with diethylether and posterior clean-up with C18 cartridges is carried out. Recovery percentages close to 100% have been calculated with different red wine samples. The accumulation of analyte in the electrode is carried out at +0.60 V for 60 s, in the presence of 0.10 M HClO 4 and 10% of ethanol; the measurement stage is performed after a medium exchange, in 0.10 M HClO 4 and 30% of ethanol. The standard addition method was employed for the analysis of real samples, since a matrix effect is observed in red wine extract. The method has been applied to several commercial red wines samples, and the results have been satisfactorily validated by HPLC.

Voltammetry of resazurin at a mercury electrode

AbstractElectrochemical behavior of resazurin on HMDE in Britton-Robinson (B-R) buffers (pH 2.0–10.0) was studied using the square-wave voltammetry (SWV), square-wave adsorptive stripping voltammetry (SWAdSV), and cyclic voltammetry (CV) techniques. The voltammogram of resazurin in B-R buffer at pH &lt; 4.0 exhibited two cathodic reduction peaks. The voltammetric peaks were obtained at −0.144 V (reversible) and −1.250 V (irreversible) at pH 3.2, and correspond to the reduction of resorufin to dihydroresorufin and to the catalytic hydrogen wave, respectively. At pH &gt; 4.0, a new irreversible cathodic reduction peak, assigned to the protonation of N-oxide on the phenoxazin ring, was observed. Electrochemical parameters (I p/E p, I p/v, I p/pH, I p/t acc) of the compound were determined. From the voltammetric data, electrochemical reduction mechanisms for all peaks have been suggested. Maximum peak current for the reversible peak was obtained at pH 4.1. A linear relationship between the current and concentration was determined, and also the lowest detection limit was found as 3.25 × 10−8 mol L−1 and 1.98 × 10−10 mol L−1 for SWV and SWAdSV, respectively.

Optimization of experimental parameters in the determination of zinc in sea water by adsorptive stripping voltammetry

A procedure for the determination of zinc in sea water by square wave adsorptive stripping voltammetry (SWAdSV) using 8-hydroxyquinoline (oxine) as an adsorbing and complexing agent has been optimized. First, a univariate study of the Zn-Ox complex peak current as a function of pH was carried out choosing values at which adequate currents were obtained. Then, selection of the experimental conditions was made using a multivariate experimental design. Variables like pH, oxine concentration (Cox), adsorption time (tads) and adsorption potential (Eads) were optimized. The first optimization step was a 24 factorial design with 16 measurements made choosing high and low levels, and three measurements at the central point (Zn(II) 10.0 μg L-1). Analysis of variance showed that pH and Cox were the most significant factors, while tads and Eads were not significant and were kept constant in later measurements. Next, to find the optimum values for pH and Cox a 22 + star factorial design was used. The best experimental parameters were pH = 6.0; Cox = 25 μmol L-1; tads = 10 s and Eads = -0.70 V. Under these conditions the peak current was proportional to the concentration of zinc over the 0.1-48.0 μg L-1 range, with a detection limit of 0.05 μg L-1. Reproducibility for 5.0 μg mL-1 Zn(II) solution was 1.9 % (n = 16). The method was validated using spiked synthetic sea water (ASTM D665), sea water reference material (CRM-SW. Zn 5 μg kg-1) and fortified water reference material (GBW08607. Zn 5 mg kg-1) with satisfactory results. Finally, the method was successfully applied to the determination of Zn(II) in sea water samples without prior treatment.

Determination of zinc by square-wave adsorptive stripping voltammetry using alizarin as a chelating agent

The adsorptive collection of zinc(II) complex with alizarin ligand, coupled with the square-wave voltammetric technique at the hanging mercury drop electrode, yields a very sensitive electroanalytical procedure for the determination of zinc. The optimized experimental conditions include: supporting electrolyte (carbonate buffer), pH (11), alizarin concentration (1×10−6moll−1), accumulation time (60s), accumulation potential (−0.1V), scan rate (700mVs−1), pulse amplitude (0.06V) and SW frequency (80Hz). The monitored stripping voltammetric current was linear over the range of 5×10−8 – 4×10−7moll−1 and the detection limit was 1×10−8moll−1. The relative standard deviation was calculated as 1.3% (n=10) for 1×10−8moll−1 Zn(II) and the obtained electrochemical signal was stabile for up to 60min. Possible interferences by either co-existing metal ions or other chelating agents were also investigated. The applicability of the proposed SW-AdSV method to the analysis of foodstuff was assessed by the determination of zinc content in instant coffee samples. The accuracy of the obtained voltammetric analytical results was validated by comparing with that obtained by atomic absorption spectrometric method and conducting the necessary statistical evaluation.

Electrochemical Behavior of Ornidazole and its Adsorptive Stripping Determination in Pharmaceuticals

The elecrochemical behavior of ornidazole was investigated using various voltammetric methods. The number of electrons transferred and diffusion coefficient were calculated by using cyclic voltammetry and bulk electrolysis techniques. It is determined that ornidazole is adsorbed on the hanging mercury drop electrode (HMDE) by using cyclic voltammetric data. Therefore, sensitive adsorptive stripping voltammetric methods for the determination of ornidazole at HMDE were developed. A systematic study of various experimental conditions was examined by using differential pulse adsorpive stripping voltammetry (DPAdsSV) and square wave adsorptive stripping voltammetry (SWAdsSV). This electroanalytical procedure enabled to determine ornidazole in the concentration range 8.0x10-7-1.0x10-5 molL-1 for both DPAdsSV and SWAdsSV. The detection and quantification limits were found to be 7.6x10-8 and 2.6x10-7 for DPAdsSV and 3.4x10-8 and 1.3x10-7 mol L-1 for SWAdsSV, respectively. The methods were applied to three different commercial pharmaceutical capsule preparations.The data obtained from commercial preparations were compared with those from a published spectrophotometric method. No difference was found statistically.

Square-Wave Adsorptive Stripping Voltammetry for Trace Determination of Dimoxystrobin and Azoxystrobin in Potatoes and Grapes

Square-wave voltammetry was used for trace determination of azoxystrobin and dimoxystrobin in potatoes, grapes, and grape juice. Experimental conditions have been optimized to achieve simultaneous determination of these analytes using the hanging mercury drop electrode. Supporting electrolyte was HCl 0.1 mol L−1, and other optimized conditions were deposition potential (−300 mV), deposition time (30 s), amplitude (150 mV), frequency (150 Hz), and step height (2 mV). Azoxystrobin and dimoxystrobin redissolution peaks presented their maxima, respectively, at −928 mV and around −650 mV. Linear and homoscedastic analytical responses (r2 > 0.99) have been observed. Limits of quantification as low as 119 µg L−1 (in grape juice) and 45 µg kg−1 (in potatoes and grapes) were found. A previous solid-phase extraction was necessary to eliminate interferences from potato and grape samples. For grape juice, no sample treatment was required. Satisfactory recoveries (from 72.3% to 96.7% for dimoxystrobin and from 81.7% to 102.3% for azoxystrobin) were found. Interferences from other strobilurins (piraclostrobin and picoxystrobin) were evaluated.

Determination of Carmine Food Dye (E120) in Foodstuffs by Stripping Voltammetry

The behavior of the food colorant agent carmine (E120) was studied by square-wave adsorptive stripping voltammetry (SW-AdSV) at the hanging mercury drop electrode. It was observed that carmine gave a sensitive stripping voltammetric peak at -350 mV in pH 3 acetate buffer. The cyclic voltammetric technique was also used to characterize the electrochemical reduction process of carmine. The adsorptive voltammetric signal was evaluated with respect to various experimental conditions, and the optimized values were supporting electrolyte, acetate buffer; buffer acidity, pH 3; dye concentration, 3 x 10(-7) M; accumulation time, 150 s; accumulation potential, -0.2 V; scan rate, 300 mV/s; pulse amplitude, 185 mV; SW frequency, 20 Hz; working electrode area, 0.6 mm2; and convection rate, 2600 rpm. The SW-AdSV peak currents depended linearly on the concentration of carmine from 5 x 10(-8) to 1.25 x 10(-7) mol/L (r = 0.99). A detection limit of 1.43 x 10(-9) mol/L with an RSD of 2.2% and a mean recovery of 97.9% were obtained. Possible interferences by several substances usually present in food products such as food additive dyes (E102, E100, E123, E127, and E129), artificial sweeteners, preservatives, and antioxidants were also evaluated. The proposed electrochemical procedure was successfully applied to the determination of carmine food dye in spiked commercially available ice cream and soft drinks.

DETERMINATION OF PESTICIDE DIAZINON BY ADSORPTIVE SQUARE-WAVE STRIPPING VOLTAMMETRY WITH DROPPING MERCURY ELECTRODE

A method for trace determination of the pesticide Diazinon using adsorptive square-wave stripping voltammetry (AdSWSV) at the dropping mercury electrode (DME) was described. The pesticide was accumulated at the DME and a well-defined stripping peak was obtained at -1012 mV vs Ag/AgCl/KCI electrode in 0.4 N ammonium acetate electrolyte soluti pH 4.3. Peak current was linear over Diazinon concentration range of 800 – 3200 ppb. Detection limit was 16.49 ppb. Effects of some other pesticides (Chlorpyrifos and Cypermethrin) on Diazinon peak and the recovery of Diazinon from artichoke leaves were studied. The method was extended to the determination of Diazinon in artichoke leaves. The recovery of Diazinon from artichoke leaves was 90.31 - 93.55%. Detection limit was 29.82 ppb. Method had high repeatability and selectivity.

Determination of Fenitrothion in River Water and Commercial Formulations by Adsorptive Stripping Voltammetry with a Carbon Ceramic Electrode

A sol-gel carbon ceramic electrode (CCE) without any assigned electron transfer mediator or specific reagents was used for the determination of fenitrothion by square-wave adsorptive stripping voltammetry. Fenitrothion strongly adsorbs on a CCE surface, which enables the development of facile electrochemical quantitative methods. Operational parameters such as pH value, initial potential value, and pulse frequency were optimized, and the stripping voltammetric performance was studied by using square-wave voltammetry. Square-wave adsorptive stripping voltammetry was used to obtain calibration curves with 2 linear ranges, 0.005-0.1 and 0.1-50 microM; the lower linear range was used to calculate the detection limit, 0.0016 microM (5 min adsorption). The effect of interference species on the determination of fenitrothion was also studied. The inherent stability, high sensitivity, low detection limit, and low cost of analysis are the advantages of this sensor. The present method was successfully applied to the determination of fenitrothion in a commercial formulation and river water samples. Analysis of real water samples by using the sensor demonstrated the feasibility of applying the sensor to the on-site monitoring of organophosphate compounds.

Direct Electroanalytical Determination of Fluvastatin in a Pharmaceutical Dosage Form: Batch and Flow Analysis

The reduction of luvastatin (FLV) at a hanging mercury-drop electrode (HMDE) was studied by square-wave adsorptive-stripping voltammetry (SWAdSV). FLV can be accumulated and reduced at the electrode, with a maximum peak current intensity at a potential of approximately −1.26 V vs. AgCl/Ag, in an aqueous electrolyte solution of pH 5.25. The method shows linearity between peak current intensity and FLV concentration between 1.0 × 10−8 and 2.7 × 10−6 mol L−1. Limits of detection (LOD) and quantification (LOQ) were found to be 9.9 × 10−9 mol L−1 and 3.3 × 10−8 mol L−1, respectively. Furthermore, FLV oxidation at a glassy carbon electrode surface was used for its hydrodynamic monitoring by amperometric detection in a flow-injection system. The amperometric signal was linear with FLV concentration over the range 1.0 × 10−6 to 1.0 × 10−5 mol L−1, with an LOD of 2.4 × 10−7 mol L−1 and an LOQ of 8.0 × 10−7 mol L−1. A sample rate of 50 injections per hour was achieved. Both methods were validated and showed to be precise and accurate, being satisfactorily applied to the determination of FLV in a commercial pharmaceutical.

Determination of trace cobalt(II) by adsorptive stripping voltammetry on disposable microfabricated electrochemical cells with integrated planar metal-film electrodes

This work reports the determination of trace Co(II) by adsorptive stripping voltammetry on disposable three-electrode cells with on-chip metal-film electrodes. The heart of the sensors was a bismuth-film electrode (BiFE) with Ag and Pt planar strips serving as the reference and counter electrodes, respectively. Metals were deposited on a silicon chip by sputtering while the areas of the electrodes were patterned via a metal mask. Co(II) was determined by square wave adsorptive stripping voltammetry (SWAdSV) after complexation with dimethylglyoxime (DMG). The experimental variables (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 3 σ limit of detection was 0.09 μg l −1 of Co(II) (for 90 s of preconcentration) and the relative standard deviation for Co(II) was 3.8% at the 2 μg l −1 level ( n = 8). The method was applied to the determination of Co(II) in a certified river water sample. These mercury-free electrochemical devices present increased scope for field analysis and μ-TAS applications.

Electrochemical behavior of valsartan and its determination in capsules

Electrochemical behavior of valsartan has been carried out in Britton–Robinson (B–R) buffer solution at pH 7.0 at the mercury film electrode (MFE) by cyclic, linear sweep, differential-pulse and square-wave voltammetry. The property of valsartan adsorption at the MFE using accumulation potential of +0.10 V was observed. The effects of experimental parameters on electrochemical process at the MFE were discussed. Differential-pulse adsorptive stripping and square-wave adsorptive stripping voltammetry for the valsartan determination were proposed, linearity was found in the range of 6.0 × 10 −8 to 4.0 × 10 −6 mol/L. The detection limits were 2.93 × 10 −9 and 3.27 × 10 −9 mol/L, respectively. The proposed methods were also applied to the commercial valsartan with good recoveries.

Disposable mercury-free cell-on-a-chip devices with integrated microfabricated electrodes for the determination of trace nickel(II) by adsorptive stripping voltammetry

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 3 σ 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.

Adsorptive stripping square wave voltammetry (Ad-SSWV) accomplished with second-order multivariate calibration: Determination of fenitrothion and its metabolites in river water samples

A method, using stripping square wave voltammetry (Ad-SSWV), for the simultaneous determination of fenitrothion (FEN) and its metabolites: fenitrooxon (OXON) and 3-methyl-4-nitrophenol (3-MET) in environmental samples is reported. All three compounds produce, at mercury electrode (HMDE), an electrochemical signal due to an adsorptive–reductive process. The electrochemical approach shows a very high overlap degree for FEN and OXON voltammograms, however the adsorption kinetic profile could be used as an additional differential variable between both analytes. Second-order multivariate calibration has been tested to solve the mixture of the three compounds. The second-order assayed methods were parallel factor analysis (PARAFAC), unfolded partial least squares (U-PLS), multidimensional partial least squares (N-PLS) and the latest ones were used in combination with the residual bilinearization procedure RBL. U-PLS/RBL model was stated as the best second-order algorithm for the simultaneous determination of these three compounds up to 50 ng mL −1 for each analyte. The detection limits and recovery values were 1.6 ng mL −1 and 92 ± 7% for FEN; 3.7 ng mL −1 and 101 ± 9% for OXON and 0.6 ng mL −1 and 97 ± 8% for 3-MET.

Determination of fenthion and fenthion-sulfoxide, in olive oil and in river water, by square-wave adsorptive-stripping voltammetry

Square-wave adsorptive-stripping voltammetry technique has been used to develop a method for the determination of fenthion in olive oil. Due to the fact that fenthion does not give any electrochemical signal at mercury electrode, the method has been based on a previous oxidation of fenthion to its metabolite, fenthion-sulfoxide, by using KMnO 4. The metabolite gives rise to a peak due to an adsorptive-reductive process at −0.786 V. Fenthion is isolated from olive oil by carrying out a solid–liquid extraction procedure using silica cartridge, followed by a liquid–liquid partitioning with acetonitrile. The detection limit in olive oil is 78.8 ng g −1 and recoveries for four levels of fortification are ranged from 85% to 109%. On the other hand, it has been developed a method for the simultaneous determination of fenthion and its metabolite fenthion-sulfoxide, in river water. Pesticides are isolated from water by carrying out a liquid–liquid partitioning with trichloromethane. The detection limits are 0.41 ng g −1 and 0.44 ng g −1, for fenthion and fenthion-sulfoxide, respectively. Recoveries for three levels of fortification are ranged from 96% to 103% for fenthion and 94% to 104% for fenthion-sulfoxide.