Solid Amalgam Electrode Research Articles

Voltammetric determination of genotoxic 4‐nitroindane at a mercury meniscus modified silver solid amalgam electrode

AbstractA silver solid amalgam electrode modified with mercury meniscus (m‐AgSAE) was used as a non‐toxic replacement of mercury electrodes in the voltammetric determination of genotoxic environmental pollutant 4‐nitroindane (4‐NI). The m‐AgSAE was used to characterize of the overall electrode process during the 4‐NI conversion using cyclic voltammetry (CV), and it was shown that the electrochemical reduction of 4‐NI is an irreversible process controlled by both diffusion and adsorption. Techniques of direct current voltammetry (DCV) and differential pulse voltammetry (DPV) at the m‐AgSAE were optimized for the development of a method for the sensitive determination of 4‐NI. The application of the more convenient DPV method was proven on authentic drinking and river water samples. Limits of quantification (LQs) obtained under the following optimal conditions were 0.1 μmol L−1 for DCV at the m‐AgSAE (Britton‐Robinson (BR) buffer pH 5.0–methanol (1 : 1); regeneration potentials E1,reg=−200 mV, E2,reg=−1100 mV) and 0.1 μmol L−1 for DPV at the m‐AgSAE (BR buffer pH 9.0–methanol (1 : 1); regeneration potentials E1,reg=−300 mV, E2,reg=−1300 mV). An attempt to decrease the LQ of the 4‐NI determination by differential pulse adsorptive stripping voltammetry at the m‐AgSAE was not successful. The LQs for DPV at the m‐AgSAE in authentic samples of drinking and river water were 1.0 μmol L−1 and 2.0 μmol L−1 (BR buffer pH 9.0–drinking or river water (1 : 9); regeneration potentials E1,reg=−300 mV, E2,reg=−1300 mV), respectively.

Rapid and straightforward electrochemical approach for the determination of the toxic food azo dye tartrazine using sensors based on silver solid amalgam

The research paper reports for the first time the investigation of the electrochemical reduction of the synthetic food azo dye tartrazine (TZ) on three different types of silver solid amalgam electrodes (AgSAEs), in particular, the polished one (p-AgSAE), covered by mercury film (f-AgSAE) or by mercury meniscus (m-AgSAE), and the comparison with dropping mercury electrode. The highest reduction peak of TZ on AgSEAs was obtained in the Britton-Robinson buffer (pH 3.4). It was shown that the accumulation step can considerably increase the peak height of TZ reduction. Two adsorptive stripping voltammetric techniques, the linear sweep (LS-AdSV) and the differential pulse (DP-AdSV), were used to develop the simple, rapid, and sensitive methods for the determination of TZ based on its reduction on the working AgSAE. The results showed that all three AgSAEs can be applied for electroanalysis of TZ, however, the best limit of detection (0.078 μmol L−1) and the limit of quantification (0.24 μmol L−1) were obtained for m-AgSAE using LS-AdSV. The developed procedures were successfully applied for TZ determination in soft drink, succade, and veterinary drug using a standard addition method. Therefore, the AgSAEs have been demonstrated to be beneficial electrochemical tools for food products’ quality and safety monitoring.

A New Approach in the Electrochemical Determination of Folic Acid in Foods: Use of a Polished Silver Solid Amalgam Electrode

A New Approach in the Electrochemical Determination of Folic Acid in Foods: Use of a Polished Silver Solid Amalgam Electrode

Electrochemical behavior of methylene blue at bare and DNA-modified silver solid amalgam electrodes

Electrochemical behavior of methylene blue at bare and DNA-modified silver solid amalgam electrodes

Application of silver solid amalgam electrodes in electrochemical detection of DNA damage.

In this study, a mercury meniscus-modified silver solid amalgam electrode was used for the first time for the detection of UV-induced DNA damage. The integrity of the double-stranded DNA (dsDNA) layer was detected indirectly using the evaluation of the methylene blue reduction within its accumulation into dsDNA after the UV irradiation of the biosensor surface with two different wavelengths (254nm and 365nm), monitored by differential pulse voltammetry. Moreover, a simple electrochemical characterization of the biosensor surface was performed using cyclic voltammetry of the redox indicator hexaammineruthenium chloride (RuHex) present in the solution. Electrochemical impedance spectroscopy (EIS) was used in both cases for the verification of results. Individual electrochemical signals depend on the time of biosensor exposure to UV irradiation as well as on the selected wavelengths and are different for both used types of dsDNA (salmon sperm and calf thymus). The highest degradation degree up to 60% was observed using sensitive EIS of methylene blue after 10min irradiation of the biosensor at 254nm. The use of RuHex seems to be less sensitive for the detection of dsDNA structural changes, when the degradation degree up to 40% was observed, using EIS at the same conditions.

Voltammetric determination of sulfur in biodiesel microemulsion using a silver solid amalgam electrode.

Monitoring sulfur in biodiesel is of fundamental importance because even in low concentrations, it can harm the operation of the engine parts and increase the emission of toxic gases and particulate material. Hence, a simple, quick and sensitive adsorptive stripping voltammetry (AdSV) method based on a silver solid amalgam electrode (AgSAE) was developed to determine sulfur in biodiesel. The novel electrochemical method was evaluated through the linear sweep adsorptive stripping voltammetry (LSAdSV), square wave adsorptive stripping voltammetry (SWAdSV) and differential pulse adsorptive stripping voltammetry (DPAdSV) in a NH3/NH4+ buffer solution (pH 9.0), containing Na2SO3. The method was applied in biodiesel microemulsion samples under optimal conditions. To this end, a ternary phase diagram was constructed, employing three components: biodiesel/propan-1-ol/buffer solution. The microemulsion with the best response was found to be 25% NH3/NH4+ buffer (pH 9.0), 5.0% biodiesel and 70% propan-1-ol. The method reached a detection limit in the order of 10-7 mol L-1 of sulfur, and recovery values between 80% and 116%. The method was applied in the determination of sulfur in biodiesel, and the amount in the samples was found to be below the value stipulated by the regulatory agencies. The method can be a promising alternative for determining sulfur in the microemulsion of biodiesel, with the ability to provide a fast response regarding the quality of this biofuel.

The Alternative Voltammetric Method for the Determination of Nicotine and Its Metabolite Nicotine N-Oxide

In the present paper, for the first time, the electrochemical behaviour of nicotine metabolite nicotine N-oxide (NNO) on static mercury dropping electrode (SMDE) and mercury meniscus modified silver solid amalgam electrode (m-AgSAE) has been reported. Nicotine N-oxide is reduced forming one peak at the potential −0.78 V on SDME and −0.86 V on m-AgSAE in Britton-Robinson buffer medium at pH 4.5 using cyclic voltammetry (CV). One electron and one proton take part in the reaction of NNO reduction. Calibration graphs for NNO determination using linear sweep voltammetry (LSV) on SDME and square-wave voltammetry (SWV) and differential pulse voltammetry (DPV) on m-AgSAE were obtained. Limit of detection (LOD) is 0.13 μM on SDME, and 0.16 μM (SWV) and 0.29 μM (DPV) on m-AgSAE. Since NNO can be used as an analytical form for nicotine voltammetric determination, so the developed methods were applied for the analysis of pharmaceutical preparations, and the recoveries from 97.3% to 104.6% were achieved. Also, the elaborated methods were used in the analysis of biological fluids, and tobacco products. The obtained results were compared to those indicated in the certificates of drugs analysis, and to the results, obtained by reference methods (HPLC and GC).

Enhancing the mediated electrochemical reduction process combined with developed liquid-gas electrochemical flow sensors for sustainable N2O removal at room temperature

New electrocatalysts with high reduction efficiency are needed to upgrade the mediated electrochemical reduction for real applications. In addition, automation is required to quantify active electrocatalysts in alkaline media and air pollution. In this study, N2O was removed sustainably by electrogenerated low valent nickel(I) phthalocyanine tetrasulfonate [Ni(I)TSPc] in 1 M KOH using an electroscrubbing system. Ni(I)TSPc electro generation and N2O removal were automated by two (liquid/gas) electrochemical flow sensors, respectively. The Ni(I)TSPc was generated electrochemically up to 95% in 1 M KOH, and high removal efficiency (100%) was observed for 5 ppm N2O and 90% for 10 ppm N2O. A limiting potential change in the in-situ LSV of the chemically synthesized Ni(I)TSPc was taken and derived from the calibration plot and validated by an ex-situ potentiometric titration using an oxygen reduction potential electrode. Using the obtained calibration plot, electrogenerated Ni(I)TSPc allowed a direct determination in a liquid flow cell. The gas flow sensor developed using a KOH/Ni(II)CN4 (TCN (II))-fabricated silver solid amalgam electrode showed an excellent response to N2O concentrations up to 32 ppm. A calibration plot with known concentration was derived and validated by gas chromatography. The response time and sensitivity obtained were approximately 500s and −0.012 mA ppm−1 cm−2, respectively. The sensor stability test confirmed its good stability. Finally, the developed in-situ electrochemical flow sensors were applied to the sustainable automation of N2O pollutant removal.

Enhanced sustainable electro-generation of a Ni (I) homogeneous electro-catalyst at a silver solid amalgam electrode for the continuous degradation of N2O, NO, DCM, and CB pollutants

This paper reports the sustainable and enhanced generation of a Ni(I) active electro-catalyst using AgSAE as a cathode material for the sustainable degradation of N2O, NO, dichloromethane (DCM), and chlorobenzene (CB) by electroscrubbing in a series operation. The AgSAE electrode showed 1.66 times higher Ni(I) formation than the Ag metal electrode. The AgSAE achieved 20% ± 2% Ni(I) generation in a highly concentrated alkaline medium, whereas Ag metal only achieved 12% ± 2% Ni(I) generation at the same current density. Electrochemical impedance spectroscopy and voltammetric studies determined that the kinetics of the charge-transfer reaction was also preferential at the AgSAE, with the cathodic peak at −1.26 V vs. Ag/AgCl confirming Ni(I) formation. Initially, the change in the oxygen reduction potential and reduction efficiency of Ni(I) confirmed the removal of N2O, NO, DCM and CB. In addition, the gas Fourier transform infrared (FTIR) spectrum revealed 99.8% removal efficiency of toxic pollutants. Therefore, the regeneration of Ni(I) confirmed the sustainable removal of toxic pollutants. Furthermore, the FTIR spectra revealed the formation of NH3 during the reduction of N2O and NO. On the other hand, DCM and CB were reduced to benzene derivatives in the solution phase. In addition, a plausible reduction mechanism was derived. As a result, the AgSAE cathode exhibited two-fold higher removal efficiency of N2O, NO, DCM, and CB than the previously reported electrodes.

Ultrasensitive determination of selenium in foodstuffs and beverages using an electroanalytical approach

This work describes the development of an electroanalytical methodology to the determination of nanomolar levels of selenium, which is sensitivity, selectivity, simple, low cost, quickness, and robustness. Therefore, it was employed a silver solid amalgam electrode modified by a thin and stable mercury film (f-AgSAE) allied to square-wave cathodic adsorptive stripping voltammetry (SWCASV). Besides this, the adsorptive and square-wave voltammetry parameters were previously optimized following the built of analytical curves in the linear range from 1.00 × 10−7 to 8.00 × 10−6 mol L−1, that resulted in a correlation coefficient of 0.9989, repeatability of 1.64%, reproducibility of 4.90%, detection limit of 1.01 × 10−9 mol L−1 and quantification of 3.36 × 10−9 mol L−1. This methodology proposed can be compared with similar data obtained by sophisticated spectroscopic techniques and other electroanalytical techniques. The procedure proposed was applied to selenium determination in in natura food (apple, orange, potato, spinach and tomato) and beverage (coconut water, soy juice and soy milk) samples. These samples were digested using a simple procedure that resulted in very satisfactory recovery percentages, confirming suitable robustness of the proposed methodology.

Electrochemical Determination of Trifluralin Herbicide Using Silver Solid Amalgam Electrode: Application in Fresh Food Samples

This paper reports the use of polished silver solid amalgam electrode (p-AgSAE) allied to square wave voltammetry (SWV) in the development of a simple, sensitive, fast and green electroanalytical methodology for the trifluralin herbicide determination in fresh food samples. The experimental (supporting electrolyte and potential and time accumulation) and voltammetric (pulse frequency, pulse amplitude and scan increment potential) parameters were previously optimized, which were employed in the construction of analytical curves. Therefore, these curves have enabled the calculation of analytical parameters (linearity range, equation of the analytical curves, coefficients of determination, limits of detection and quantification, recovery efficiency, and relative standard deviations for intraday and interday experiments) and they indicated that the use of the p-AgSAE is suitable for determining any contamination by trifluralin. So, the proposed methodology had to minimize the toxic residues due to the use of liquid mercury or the adsorbed products from the redox reaction that promotes passivation in the other solid surfaces. Furthermore, the optimized methodology was used to trifluralin determination in eggplant, carrot, tomato, grape juice and orange juice, and the results indicated that the proposed methodology presented high robustness, stability and sensitivity, good reproducibility, and hence it is applicable for complex samples.

Voltammetric Behavior and Reliable Method for the Determination of Coccidiostat Robenidine in Animal Feed and Poultry Meat

AbstractThe voltammetric behaviour of coccidiostat robenidine was investigated. The outcomes have revealed that reduction of robenidine causes an appearance of one diffusion‐controlled cathodic peak on a static mercury drop electrode (SMDE) and a silver solid amalgam electrode (p‐AgSAE). The influence of pH, a supporting electrolyte, a scan rate and accumulation parameters was evaluated. The mechanism of robenidine reduction involving two electrons and one proton was studied for the first time. The calibration curves with the wide linear concentration ranges (more than two concentration orders) were obtained under optimized experimental conditions and operating parameters. The reduction current linearly increases when increasing the concentration of coccidiostat. The methods of voltammetric determination of robenidine in feed and meat have been developed. The limits of quantitation of the methods of robenidine determination in feed are 9.5 mg/kg and 2.5 mg/kg on SMDE and p‐AgSAE, respectively. Calculated recoveries ranges of robenidine were between 88.8 % and 101.5 %.

Determination of heavy metal poisoning antidote 2,3-dimercapto-1-propanesulfonic acid using silver solid amalgam electrode

Voltammetric behavior of heavy metal poisoning antidote 2,3-dimercapto-1-propane-sulfonic acid (DMPS) was investigated using linear scan voltammetry (LSV), differential pulse cathodic stripping voltammetry (DPCSV), differential pulse anodic stripping voltammetry (DPASV), and elimination voltammetry with linear scan (EVLS) at a polished (p-AgSAE) and at a meniscus modified (m-AgSAE) silver solid amalgam electrode. It was confirmed that the mechanism of the electrode process involves two consecutive reductive desorptions with coupled proton/electron transfer preceded by a kinetic process prominent at higher scan rates as revealed by EVLS. Voltammetric and complexation behavior of DMPS in the presence of Pb2+ was further investigated by DPASV and DPCSV titrations confirming reductive desorption, complex formation, and transmetalation. Optimum conditions for DPCSV were as follows: Britton-Robinson buffer (BRB) of pH 10, Eacc = −200 mV and tacc = 30 s for p-AgSAE and BRB of pH 5, Eacc = 0 mV and tacc = 15 s for m-AgSAE. Limits of quantification (LOQs) and detection (LODs) were 0.3 and 0.1 μmol L−1 at m-AgSAE and 0.8 and 0.3 μmol L−1 at p-AgSAE, respectively. The practical applicability of the newly developed method was verified by determination of DMPS in commercial drug Dimaval and in human urine samples.

Cathodic stripping voltammetric determination of β-cyfluthrin, a pyrethroid insecticide, using polished silver solid amalgam electrode

This work describes an electroanalytical procedure for determination of beta-cyfluthrin (βCF), a pyrethroid insecticide, using polished silver solid amalgam electrode (p-AgSAE) allied to a square-wave cathodic adsorptive stripping voltammetry (SWCASV). Although βCF is non-electroactive in the conventional electrodes, it was accumulated at the p-AgSAE surface as adsorbed mercury salt, allowing their indirect determination using the well-defined reduction peak of mercury complex at − 0.94 V, obtained after adequate experimental and voltammetric optimization. Analytical curves were constructed for βCF, and all analytical parameters were properly evaluated. The proposed methodology was applied in the βCF determination in natural water and tea samples, which were previously filtrated before voltammetric analysis, already the same analysis performed using gas chromatography with mass spectroscopy detection technique employed the solid-phase extraction step. Analytical parameters obtained using both techniques indicated no significant difference at 95% confidence, confirming that the electroanalytical procedure had high robustness, good stability and suitable sensitivity to determination of βCF in complex samples.

Acetylcholinesterase-choline oxidase-based mini-reactors coupled with silver solid amalgam electrode for amperometric detection of acetylcholine in flow injection analysis

A stable and simple amperometric biosensor based on the separated bienzyme (acetylcholinesterase (AChE) – choline oxidase (ChOx)) part has been successfully developed for the determination of acetylcholine (ACh) using flow injection analysis for the first time. The bienzyme part consists of two consecutively connected enzymatic mini-reactors filled by mesoporous silica powders (SBA−15) covalently covered by AChE and ChOx, respectively. The oxygen consumption as the result of two sequential enzymatic reactions was monitored amperometrically. The wall-jet cell with working silver solid amalgam electrode covered by mercury film was used for four-electron oxygen reduction at the highly negative potential. The experimental parameters including the amounts of immobilized enzymes, pH of the carrier solution, the detection potential, flow rate, and injection volume of ACh were optimized. The detection limit was found to be 4.1 μmol L−1. The interfering effect of 1.0 mmol L−1 glucose, 0.1 mmol L−1 uric acid, and 0.1 mmol L−1 ascorbic acid to 0.1 mmol L−1 ACh was 0.6%, 2.2%, and 2.8%, respectively. The developed amperometric ACh biosensor showed 59.8% of its initial response after >400 measurements over 100 days.

A New Approach for Voltammetric Determination of Nefopam and its Metabolite

AbstractIn present paper we described a new simple voltammetric method of determination of nefopam alkaloid and its metabolite – N‐oxide. N‐oxide of nefopam is reduced at the dropping mercury electrode (DME) and silver solid amalgam electrodes (AgSAE), which can effectively replace mercury and chemically modified electrodes. The reduction consists of two one‐electron stages each accompanied with one proton transfer. N‐oxide of nefopam can be obtained from nefopam substance by oxidation with potassium peroxymonosulfate. It was studied the effect of various factors on N‐oxide quantitative yield (pH, oxidation duration, reagents concentration) as well as on the reduction of N‐oxide at DME and p‐AgSAE (pH, the nature of background electrolyte, potential and time of accumulation). It was showed that the reduction current linearly increased with increasing of concentration of analgesic. Limit of quantiation is 10−6 mol L−1 at DME and 10−7 mol L−1 at p‐AgSAE. The developed method was applied for the analysis of commercial drug solution for injection “Nefopam” with recovery of 96.7 %, as well as for the spiked human urine samples. Excellent repeatability with a relative standard deviation below 5 % was achieved.

Electrochemical study and simultaneous voltammetric determination of contraceptives ethinylestradiol and cyproterone acetate using silver nanoparticles solid amalgam electrode and cationic surfactant

In this work we propose the voltammetric analysis of contraceptive hormones ethinylestradiol (EE) and cyproterone acetate (CPA) using solid amalgam electrode fabricated with silver nanoparticles. To the best of our knowledge, this is the first report describing the simultaneous determination of these two compounds and also the first report of the use of amalgam electrode for analysis of EE and CPA. The voltammetric behavior of both substances was investigated by their reduction. An irreversible electrochemical process involving two protons and two electrons was found for each compound. The analytical assays were carried out using staircase voltammetry (SCV). Due to this, aiming to improve the analytical sensitivity, the cationic surfactant cetyltrimethylammonium bromide was also used. The instrumental and experimental parameters were studied and optimized to achieve the best conditions for the analysis. Under the optimum conditions, the voltammetric signals of EE and CPA showed dependence on the concentration range from 6.4 × 10−7 to 7.8 × 10−6 mol L−1 and from 1.0 × 10−6 to 1.0 × 10−5 mol L−1, respectively. The limits of detection obtained were 1.03 × 10−7 mol L−1 for EE and 2.99 × 10−7 mol L−1 for CPA. The analytical usefulness of the method was evaluated through its application on the simultaneous determination of EE and CPA in pharmaceutical formulations and urine samples. The two analytes were successfully quantified in these samples with good precision and the values found presented satisfactory concordance with the reference values, suggesting acceptable analytical efficiency for the approach described here.

Doxorubicin determination using two novel voltammetric approaches: A comparative study

Doxorubicin (DOX) represents an anthracycline-based antitumor and antibiotic medication. DOX determination in body fluids is relevant for treatment, monitoring, and individual dosage optimization. Two novel methods of DOX determination have been compared in this manuscript: i) differential pulse cathodic stripping voltammetry (DPCSV) on a polished silver solid amalgam electrode (p-AgSAE) in a specially designed micro-volume voltammetric cell (MVVC) and ii) differential pulse voltammetry (DPV) on a polarized liquid/liquid interface represented by a supported membrane prepared by impregnating a polyvinylidenfluoride microporous filter with a room-temperature ionic liquid (RTIL) tridodecylmethylammonium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TDMA-TFPB). Moreover, elimination voltammetry with linear scan (EVLS) has been applied for elucidation of controlling reaction processes observed at the p-AgSAE.DPCSV method on the p-AgSAE is applicable for the determination of DOX in the linear dynamic range (LDR) from 0.6 to 10 μmol L−1, with the limit of detection (LOD) of 0.44 μmol L−1. Applicability of this method was verified on analysis of spiked samples of tap water (recovery 100.6 ± 6.6%, relative standard deviation (RSD) 5.9%, on the DOX level of 1.0 μmol L−1) and human urine (recovery 100.7 ± 6.6%, RSD 4.3%, on the DOX level of 1.0 μmol L−1).Using the above-mentioned innovative liquid/liquid interface method, similar results have been achieved (LOD of 0.84 μmol L−1, LDR from 1 to 40 μmol L−1). Nevertheless, due to the presence of some interfering compounds and of charged lipophilic compounds, this method must be preceded by a separation step in the case of body fluids analysis.

Electrochemical microcell based on silver solid amalgam electrode for voltammetric determination of pesticide difenzoquat

This study presents an application of a non-toxic mercury meniscus modified silver solid amalgam electrode as a reliable, user-friendly and sensitive sensor for the determination of herbicide difenzoquat as a model pollutant in micro volumes of samples. Difenzoquat gave one cathodic peak at around –1.4 V (vs. Ag/AgCl/3 mol L–1 KCl reference electrode) independent on pH (in the range 8–12). Sharp maxima greatly influenced the peak of the analyte and they were eliminated by the addition of gelatine as a surface-active compound. The optimal supporting electrolyte was found to be Britton-Robinson (BR) buffer with pH 12. Determination of the analyte in the 10 μL volume was carried out in a newly developed simple microcell with the amalgam working electrode. A procedure for fast and reliable removal of dissolved oxygen was used. Difenzoquat was therefore successfully determined by differential pulse voltammetry in BR buffer pH 12 and in model river water samples with addition of gelatine with limits of quantification 0.41 and 0.45 μmol L–1, respectively. It was proved that this sensor can be directly used for monitoring of pollutants in volumes of tens of microliters of various samples with similar parameters as the determination in larger volumes.

Metal Exchange Reactions in Metallothioneins Explored by Electrochemical Methods

AbstractMetallothioneins (MTs) are widely occurring, small, cysteine‐rich proteins, important for essential metal (Zn, Cu) homeostasis and transport and for heavy metal (Cd, Hg) detoxification. In buffered solutions of mammalian MT, voltammetry and potentiometric striping analysis (PSA) can distinguish different coordination of bound metals or follow their exchange, especially that of zinc and cadmium for copper, silver, and cobalt. The examples of different electrode applications as of hanging mercury drop electrode (HMDE), of silver solid amalgam (AgSAE) electrode, and of silica gel modified carbon paste electrode (SiO2‐CPE) are given.