Mercury Drop Research Articles

Voltammetric determination of heavy metals in honey bee venom using hanging mercury drop electrode and PLA/carbon conductive filament for 3D printer.

A new method for determination of selected heavy metals (Cd, Pb, Cu, Zn, and Ni) in honey bee venom was developed. Heavy metals are metabolized and incorporated into bee products, including honey and honey bee venom (apitoxin). Their composition reflects contamination of “bee environment”, providing information about heavy metal contamination in the neighborhood of human dwellings. Moreover, assessment of bee products contamination is relevant for medicine, as they are a tool for promising therapeutic and chemoprophylactic strategies against COVID-19 (SARS-CoV-2). Owing to the complicated matrix, the developed method consists of wet mineralization with sulfuric acid, nitric acid, under increased temperature, and pressure and subsequent repeated boiling with concentrated nitric acid. Determination of the selected metals was carried out by anodic or cathodic stripping voltammetry on two types of electrodes: pen-type hanging mercury drop electrode (HMDE) and PLA filament with carbon conductive admixture (PLA-C) for 3D printer. Contents of lead and cadmium in all analyzed bee venom samples were on the level of mg kg−1, of nickel and copper about ten times higher, and of zinc on the level of g kg−1. The results achieved using HMDE were recorded with average relative standard deviation (RSD) 5.4% (from 3.2% to 8.6%) and using PLA-C 11.8% (from 6.5% to 18.0%). The results achieved using both electrodes proved to be equivalent with statistical probability higher than 95%.Graphic abstract

Voltammetric Determination of Catalytic Effect of Nitrite in Nitrate Media by Graphite and Mercury Electrode on Acid Red-27 Cobalt Complex

In this study, the catalytic effect of nitrite on the cobalt complex of acid red 27, which is one of the most important azo dyes today, was investigated. Voltammetric studies were carried out with a Hanging Mercury Drop electrode and pencil graphite electrode using the Cathodic AdsSWV technique in nitrate media. First, in situ formation of the complex was determined by electrochemical method. It was then observed that the voltammetric peak current of the complex increased in the presence of nitrite anions. The deposition time, potential and nitrite concentration were investigated to optimize the conditions for both electrodes. According to the results, the reaction mechanism of the catalytic effect of nitrite has been proposed.

Structural and electrochemical properties of two novel CdX2 (X = Br, I) picolinamide complexes

Two novel discrete cadmium(II) complexes, namely [CdBr2(pia)2] (1) and [CdI2(pia)2] (2) were prepared by reactions of aqueous solutions of CdX2 (X = Br, I) salts with picolinamide (pia) in the 2:1 ligand to metal stoichiometric ratio. Both compounds were characterized by elemental analysis, IR-spectroscopy, TG/DSC analyses and electrochemical methods. The electrochemical characteristics of both ligand (pia) and prepared complexes were studied by cyclic and (cyclic) square-wave voltammetry, on a static mercury drop electrode (SMDE), in aqueous media over a wide pH range. The molecular and crystal structure of the compounds was determined by the single crystal X-ray diffraction method. X-ray structure analysis of 1 and 2 have shown that the compounds are isostructural with minor differences in the bond angles of the coordination sphere. In both compounds the Cd(II) ion is coordinated by two halide atoms and two mutually orthogonal picolinamide ligands that act as N,O-chelators in a distorted octahedral arrangement. In the crystal structure, the molecules of 1 and 2 are primarily linked via strong head–to–head amide hydrogen bond interactions forming dimers. In 1 the adjacent dimers are connected via NH⋯Br hydrogen bonds and offset face to face π⋯π interactions that involve pyridine rings, while in the structure of 2, the dimers are connected via CH⋯O, CH⋯N and NH⋯I hydrogen bonds into the final 3D structure. The intermolecular interactions in both crystal structures were further studied by Hirshfeld surface analysis. Electrochemical analysis of 2-picolinamide indicates the irreversible nature of its electro-reduction reaction on SMDE at pH 2. To provide better insight into the redox mechanism and electrokinetic properties of 2-picolinamide, the study of the effect of signal frequency on CSWV response was carried out, too. The electrochemical reduction of complex 2 involves two electron transfer reactions at −0.55 V and −0.83 V, indicating two redox active centers in the molecule, while complex 1 appears to be apparently electro-inactive in the studied potential range.

Study of electrochemical behavior of escitalopram oxalate using hanging mercury drop electrode and its determination in human urine and pharmaceuticals

Escitalopram oxalate (ESC-OX) is among the most currently used antidepressant drugs. This study aimed to determine ESC-OX in human urine and different pharmaceutical dosage forms via the electrochemical method. The electrochemical behavior of ESC-OX was investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques at hanging mercury dropping electrode (HMDE). The maximum reduction potential was determined to be − 0.55 and − 0.57 V at pH 6.5 in a cell containing 5% (v/v) methanol and 0.3 M KCl. Under the optimized conditions, the calibration curve of the cathodic peak current versus the concentration was linear in the range of 4.143–29.0 µg mL−1. The LOD and LOQ were found to be 1.15 µg mL−1 and 1.31 µg mL−1, 3.490 µg mL−1 and 3.97 µg mL−1 for pharmaceutical and urine samples, respectively. The investigation of electrochemical reduction of ESC-OX on the HDME by using CV resulted in a quasi-reversibility, mainly diffusion-controlled reaction that involves a four-electron reduction of the nitrile group. For analytical purposes, a stable and well-defined peak was obtained in DPV mode. The average accuracy was found to be 101.60% ± 0.48 and 99.72% ± 5.64 for pharmaceutical and urine samples, respectively. Moreover, the developed method was precise with RSD % below 2% for both samples. The validation of the developed method was carried out as stated in the ICH Q2(R) 1 guideline. The proposed technique was effectively utilized for the determination of ESC-OX in different pharmaceutical formulations and urine samples. Neither excipients nor endogenous substances have electroactive interferences.

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 %.

Nifedipine degradation by an electro-oxidation process using titanium-based RuO2–IrO2–TiO2 mixed metal oxide electrode

The interest in new emerging pollutants (NEPs) does not only focus on the main compounds but also the degradation or intermediate products. It is important to have an effective primary treatment for the removal/degradation of NEPs from hospital and clinical wastewater to protect the environment. In this study, nifedipine degradation was performed by an electro-oxidation method using titanium-based mixed metal oxide (MMO) electrode. The determination of nifedipine was carried out by differential pulse voltammetry at hanging mercury drop electrode using Britton–Robinson buffer (BRB). The nifedipine oxidation peak was observed at + 0.7 V at a scan rate of 20 mV s−1 in BRB pH 8. Titanium-based electrodes with different metal oxide compositions were assessed as an anode material for nifedipine degradation as follows: TiO2/Ti, IrO2–TiO2/Ti, RuO2–TiO2/Ti, and IrO2–RuO2–TiO2/Ti. The electro-oxidation of nifedipine was monitored using cyclic voltammetric techniques, and the degradation intermediates were confirmed using LC–MS. Approximately 65–83% of nifedipine degradation was achieved using RuO2–TiO2/Ti and IrO2–TiO2/Ti electrodes. Interestingly, RuO2–IrO2–TiO2 electrode showed complete (100%) electro-oxidation of nifedipine at 30 min. Two nifedipine degradation intermediates were identified, namely 5-methoxycarbonyl-2,6-dimethyl-4-phenyl-1,4-dihydropyridine-3-carboxylic acid (compound I) and 2,6-dimethyl-4-phenyl-1,4-dihydropyridine-3,5-dicarbaldehyde (compound II) during the electro-oxidation process using RuO2–IrO2–TiO2 electrode. Finally, the degradation pathway of nifedipine by MMO electrode was proposed. This is the first report on the nifedipine degradation using MMO titanium electrode by the electro-oxidation process.

Electrochemical Behavior and Square-Wave Stripping Voltammetric Determination of Roflumilast in Pharmaceutical Dosage Forms.

Bronchial asthma and chronic obstructive pulmonary disease (COPD) are among the most common chronic diseases. Roflumilast is a novel, potent, selective, and long-acting phosphodiesterase 4 (PDE-4) inhibitor for the treatment of bronchial asthma and COPD. It has anti-inflammatory effects, and it has been shown to reduce exacerbations and improve pulmonary function in patients with COPD. Although there have been some other analytical methodologies reported for the determination of roflumilast in pharmaceutical dosage forms, there has not yet been any electrochemical methodology proposed for determination of this unique active pharmaceutical ingredient in its dosage forms. The aim of this study was to develop an easily applied, selective, sensitive, accurate, and precise square-wave stripping voltammetric (SWSV) method for the determination of roflumilast in its pharmaceutical dosage forms. In addition, the electrochemical behavior of roflumilast was investigated. The proposed method was based on electrochemical reduction of roflumilast at a hanging mercury drop electrode (HMDE) in 0.1 M K2HPO4 and 0.1 M Na2B4O7 (1:1, v/v) buffer at pH 5.0. Two reduction peaks were observed at -1150 mV and -1260 mV with 30 s of accumulation time and -850 mV of accumulation potential time versus Ag/AgCl reference electrode. The highest peak current values with the best peak definition were observed at a frequency of 50 Hz, scan increment of 5 mV, and pulse amplitude 25 mV. The proposed method was validated by evaluating validation parameters such as linearity, sensitivity, repeatability, accuracy, precision, selectivity, recovery, robustness, and ruggedness. A good linear correlation (r=0.9948) was obtained between the electrochemical response of roflumilast and its concentration in the range of 0.74-3.05 μg mL-1 under the optimum conditions. The obtained accuracy results were between 2.04% and -2.04% while the relative standard deviation of the results was at least 2.78% for intraday and inter-day studies. The mean recovery for the real applications was 100.63% ± 0.52. The electrochemical behavior of roflumilast was investigated by cyclic voltammetry. The cyclic voltammogram of roflumilast exhibited two peaks and the reduction reaction was reversible. This developed and validated SWSV method was applied successfully for the determination of roflumilast in tablet dosage form (Daxas®) to assess active roflumilast content. Since high- -performance liquid chromatography is a dominant technique in industry for quality control of active pharmaceutical ingredients, the finding in the present study demonstrated that square-wave stripping voltammetry could be easily utilized in routine applications to determine roflumilast content in its dosage forms.

Maltol determination in food by microwave assisted extraction and electrochemical detection

An electrochemical method is proposed for the determination of maltol in food. Microwave-assisted extraction procedures were developed to assist sample pre-treating steps. Experiments carried out in cyclic voltammetry showed an irreversible and adsorption controlled reduction of maltol. A cathodic peak was observed at -1.0 V for a Hanging Mercury Drop Electrode versus an AgCl/Ag (in saturated KCl), and the peak potential was pH independent. Square wave voltammetric procedures were selected to plot calibration curves. These procedures were carried out with the optimum conditions: pH 6.5; frequency 50 Hz; deposition potential 0.6 V; and deposition time 10 s. A linear behaviour was observed within 5.0×10^(-8) and 3.5×10^(-7) M. The proposed method was applied to the analysis of cakes, and results were compared with those obtained by an independent method. The voltammetric procedure was proven suitable for the analysis of cakes and provided environmental and economical advantages, including reduced toxicity and volume of effluents and decreased consumption of reagents.

A novel catalytic adsorptive stripping voltammetric method for the determination of germanium ultratraces in the presence of chloranilic acid and the V(IV)\xb7HEDTA complex

A novel, sensitive catalytic adsorptive stripping voltammetric procedure which can be used to determine trace amounts of germanium is described. The method is based on the interfacial accumulation of the complex formed by Ge(IV) and the product of the reduction of chloranilic acid on the hanging mercury drop electrode or the renewable silver amalgam film electrode, and its subsequent reduction from the adsorbed state followed by the catalytic action of the V(IV)·HEDTA complex. The presence of V(IV)·HEDTA greatly enhances the adsorptive stripping response of Ge. The reduction of the Ge(IV) in the presence of chloranilic acid and V(IV)·HEDTA was investigated in detail and the effects of pH, electrolyte composition, and instrumental parameters were studied. Under optimal conditions, the catalytic peak current of germanium exhibited good linearity for Ge(IV) concentrations in the range of 0.75–60 nM (for 60 s of accumulation at −0.1 V, r2 = 0.995) and a low limit of detection (LOD = 0.085 nM). The procedure was successfully applied to determine Ge in water samples.

Simultaneous Determination of Thiocolchicoside and Diclofenac Diethyl Ammonium in Topical Gel Formulation by Square Wave Voltammetric Method

A rapid, simple, sensitive, precise and specific square wave voltammetric method was developed for the simultaneous determination of Thiocolchicoside (TC) and Diclofenac diethyl ammonium (DDA) in topical gel formulation. The combination of TC and DDA have synergetic action on the treatment of rheumatoid arthritis and other related conditions. The optimum conditions were obtained in Britton–Robinson buffer pH 3.00 for electroreduction at hanging mercury drop electrode. Well-defined peaks were observed for TC at –0.85 V, and for DDA at –1.18 V vs. Ag/AgCl/4.6 M KCl. Under optimum conditions, the linear response ranges for determination of TC and DDA were 1.07–24.2 µM and 5.64–45.8 µM, with detection limits of 0.54 and 3.25 µM, respectively. The electrochemical behaviors of the substances such as current type and reversibility of the electrode reactions were investigated by using cyclic voltammetry. The reduction mechanisms were also proposed. The method was validated with respect to accuracy, precision, sensitivity and specificity according to the International Conference on Harmonization guidelines. The developed method was applied for the simultaneous determination of TC and DDA in topical gel formulation including binary mixtures. The excipients present in the formulation did not interfere with the assay. The method is suitable for application in quality-control laboratories, because it is simple and rapid with high accuracy and precision.

The acid\u2013base and redox properties of menaquinone MK-4, MK-7, and MK-9 (vitamin K2) in DMPC monolayers on mercury

The acid–base and redox properties of the menaquinones MK-4, MK-7, and MK-9 (vitamin K2) have been studied in DMPC monolayers on mercury electrodes. The monolayers were prepared by adhesion-spreading of menaquinone-spiked DMPC liposomes on a stationary mercury drop electrode. All three menaquinones possess {text{p}}K_{{text{a}}} constants outside the experimentally accessible range, i.e., they are higher than about 12. The standard potentials of MK-4, MK-7, and MK-9 in the DMPC monolayers are very similar, i.e., 0.351, 0.326, and 0.330 V (corresponding to the biochemical standard potentials − 0.063, − 0.088, and − 0.085 V).Graphic abstract

A Novel Electrochemical Sensor Based on Carbon Dots-Nafion Composite Modified Bismuth Film Electrode for Simultaneous Determination of Cd2+ and Pb2+

Introduction Bismuth film electrodes (BiFEs) have become a hopeful alternative to mercury drop and film electrodes due to their non-toxicity and equal or even superior electrochemical performance towards heavy-metal-ion detection [1]. Meanwhile, various carbon nanomaterials (e.g., graphene oxide, carbon nanotubes, etc.) had been composited with bismuth for improving the sensitivity and reproducibility of BiFEs. However, one primary problem with the BiFEs is that the hydrophobicity of these carbon nanomaterials may have a negative impact on the performance of the electrodes in aqueous media.It has been reported that carbon dots (CDs), as a new hydrophilic carbon nanomaterial, may have similar properties to other carbon nanomaterials, thus CDs can be used as modified electrode materials to improve the performance of electrochemical sensors [2]. CDs have not been used for the enhancement of the electrochemical performance of bismuth-based electrodes. Due to the composited feasibility of CDs and bismuth, they have been successfully applied in photocatalysis[3] and energy storage[4]. Therefore, it would be of special potential to fabricate a novel bismuth-based electrode based on CDs for improving the electrode detection performance for heavy metals.The objective of this study is to develop inexpensive, highly selective, rapid and environmental friendly sensors for Cd2+ and Pb2+ detection. In this work, CDs, Nafion, and bismuth were deposited onto the glassy carbon electrodes (GCEs) sequentially to form a novel chemical sensor for Cd2+ and Pb2+ ions rapid detection. Methods CDs were prepared with a facile one-pot hydrothermal method using glucose as the carbon source[5]. To fabricate BiF/CDs/Nafion/GCE, the bare GCEs were polished well with a diamond suspension solution for the further modified. Then, the CDs were electrodeposited on the GCE using cyclic voltammetry in H2SO4 solution containing CDs. Finally, 5 μL of 1 wt.% Nafion film was used as an adhesive to stabilize the CDs and improve the reproducibility of the modified electrode. The obtained electrochemical sensor was abbreviated as CDs/Nafion/GCE. For comparison, Nafion/GCE was prepared using a similar method. Bismuth was in situ deposited onto the CDs/Nafion/GCE from non-deaerated HAc-NaAc (pH 4.5) buffer solution in the presence of 1000 μg L-1 Bi3+ with model target metals. A conventional three-electrode system was adopted to analyze Cd2+ and Pb2+ concentrations using an Autolab PGSTAT204 workstation (Metrohm). Conclusions Fig. 1 and Table 1 present the differential pulse voltammetry (DPV) electrochemical performance of bare GCE, Nafion/GCE, CDs/Nafion/GCE and BiF/Nafion/GCE in 0.1 M acetate buffer (pH 4.5) containing 0.25 μg mL-1 Cd2+ and Pb2+. The DPV curves of both bare GCE and Nafion/GCE display two weak stripping peaks for Cd2+ and Pb2+. After modification on the GCE surface with CDs-Nafion film, the stripping peak currents of Cd2+ and Pb2+ significantly increased, indicating that the CDs may have the ability to spur the electron transfer rate of the detection system [6]. More importantly, BiF/CDs/Nafion/GCE showed a higher sensitivity for simultaneous detection of Cd2+ and Pb2+ compared with bare GCE and CDs/Nafion/GCE. The Cd2+ current obtained with BiF/CDs/Nafion/GCE was 71.02 and 4.85 times higher than with bare GCE and CDs/Nafion/GCE, respectively. The Pb2+ current obtained with BiF/CDs/Nafion/GCE was 51.85 and 6.31 times higher than those with bare GCE and CDs/Nafion/GCE, respectively.Fig. 2 and Table 2 show the simultaneous stripping analysis of Cd2+ and Pb2+ using the BiF/CDs/Nafion/GCE. The DPV curves show individual peaks at approximate -0.75 V for Cd2+ and -0.55 V for Pb2+. The separation between two peaks was approximately 200 mV, a difference that is sufficient to detect Cd2+ and Pb2+ simultaneously and selectively. The inset in Fig. 2 presents the linear relationship between the peak currents and the concentrations of Cd2+ and Pb2+ (The linear equations: Ip=18.82C+3.49 (R2=0.994) for Cd2+ and Ip=25.12C+3.55 (R2=0.993) for Pb2+). The calculated detection limits (3δ method) for Cd2+ and Pb2+ are 0.003 and 0.002 mg L-1, respectively.The low detection limits suggest that the BiF/CDs/Nafion/GCE is a feasible sensor to simultaneously detect Cd2+ and Pb2+, which has great potential for application in the fields of environmental monitoring. Table 1. Electrochemical performances of the bare GCE, Nafion/GCE, CDs/Nafion/GCE and BiF/CDs/Nafion/GCE in simultaneous detection of Cd2+ and Pb2+. Bare GCE Nafion/GCE CDs/Nafion/GCE BiF/CDs/Nafion/GCE Cd2+ I/μA 0.116 0.045 1.697 8.239 E/V -0.782 -0777 -0.797 -0.772 Pb2+ I/μA 0.192 0.103 1.577 9.957 E/V -0.540 -0.525 -0.565 -0.520 Table 2. The analytical performance of BiF/CDs/Nafion/GCE in simultaneous detection of Cd2+ and Pb2+. Analytes Linear range (mg L-1) LOD (mg L-1) R2 Simultaneous analysis Cd2+ 0.05 - 0.50 0.003 0.994 Pb2+ 0.05 - 0.50 0.002 0.993 Keywords: Carbon points; Bismuth film; Cadmium; LeadFunding: This work was financially supported by the Major Science and Technology Program for Water Pollution Control and Treatment (Project no. 2018ZX07109003).

Determination of Methimazole in Pharmaceutical Preparation and Human Serum by Square Wave and Differential Pulse Polarographic Methods

Objectives: In this study, the polarographic behaviour of methimazole was studied using cyclic, square wave and differential pulse polarographic methods. Methods: The influence of several variables (including nature of the buffer, concentration, scan rate, drop size, etc.) was examined in square wave and differential pulse polarographic methods for methimazole. The best square wave and differential pulse polarographic responses were obtained in 0.1 M sulfuric acid. The peak currents were measured with a static mercury drop electrode at 0.10 V versus Ag/AgCl. Results: The linearity was established over the concentration range of 5-80 mg/mLfor both methods in supporting electrolyte and human serum. The methods were validated and applied to the determination of methimazole in a commercial tablet. There was no significant differences between the results obtained by square wave and differential pulse polarographic methods. Square wave and differential pulse polarographic methods are also available and applicable for the determination of mentioned substance in human serum. No electroactive interferences from the endogenous substances were found in the serum samples. Mean recovery was 99.9%. Conclusion: They were concluded that the developed methods were accurate, sensitive, precise, reproducible and useful for the quality control of methimazole in pharmaceuticals and spiked serum.

Novel Electrochemical Sensor Based on Nylon 6,6-Modified Graphite HB Pencil Electrode for Chlorothalonil Determination by Differential Pulse Cathodic Stripping Voltammetry

Mercury-based electrode was the choice of electrode material for many years, and it has been extensively used in voltammetry studies. Nonetheless, alternative electrode materials are highly preferred in voltammetry studies due to the toxicity of mercury. This work introduces a novel green sensor, nylon 6,6-modified graphite HB pencil electrode (Nyl-MHBPE) as electrochemical method for chlorothalonil determination by differential pulse cathodic stripping voltammetry (DPCSV). The Nyl-MHBPE was significantly improved electroactivity towards the reduction of chlorothalonil, under the optimal conditions (at pH 8.0). It was clearly observed that nylon 6,6 revealed as an efficient modifier for enhancing stripping signal for voltammetric analysis. Moreover, the developed sensor showed great feature such as a remarkably low detection limit in nanomolar level (0.94 × 10−8 M) with a linear range from 1 to 26 × 10−7 M. It presented excellent repeatability with high sensitivity and selectivity. Besides, analysis of chlorothalonil in real water samples was successfully carried out with good recovery values (92.5–103%) and relative standard deviation (RSD) values < 2.2%. The performance of Nyl-MHBPE was also compared to bare pencil electrode (HBPE). Another significant feature of this work is that the conductivity properties of the Nyl-MHBPE were superior as compared to hanging mercury drop electrode (HMDE). The present study provides admirable merits that make the Nyl-MHBPE selected as a promising electrochemical sensor to perform routine analysis of chlorothalonil.

Multianalyte voltammetric determination of traffic-linked metals in marine organisms employed as pollution bio-monitors

ABSTRACT A new procedure is proposed for the voltammetric determination of ultra-trace cadmium(II), copper(II), lead(II), platinum(II), palladium(II), rhodium(III) and zinc(II) by a single run of square wave adsorptive catalytic stripping voltammetry. The voltammetric cell was based on a typical three-electrodes set-up: working electrode (stationary hanging mercury drop), reference electrode (Ag|AgCl|KClsat) and auxiliary electrode (platinum). The supporting electrolyte contained the formazone complex together with dimethylglyoxime and the disodium salt of ethylenediaminetetraacetic acid. Validation of the analytical procedure was obtained by the analysis of standard reference materials (Mussel Tissue BCR-CRM 278, Oyster Tissue NIST-SRM 1566a). Comparison with spectroscopic measurements was performed. Good accuracy was achieved. The analytical procedure was finally applied to mussels and clams sampled on the mouth of Po river, employed as bio-monitors.

Dramatic changes in the electrochemical and spectroscopic behavior of DNA fragments induced by the loss of a single nucleotide

In this paper, the d(GCGAAGC) heptamer and the closely related d(GCGAGC) hexamer are examined via electrochemical (cyclic voltammetry) and spectroscopic (circular dichroism) methods. Dramatic changes in the CD spectroscopic and CV electrochemical properties, induced by the loss of only one single nucleotide (A), are detected. The CD spectra and native polyacrylamide gel electrophoresis (PAGE) confirmed structural changes taking place in the relevant chain-like oligodeoxynucleotide assemblies. Dedicated studies suggest that the heptamer (Hp) possesses a hairpin structure, whereas the hexamer (Hx) appears to be rather a duplex. Both of the structures exhibited completely different adsorption behavior at the hanging mercury drop electrode, and this factor was readily confirmed by means of elimination voltammetry with linear scan (EVLS). We established that the Hp hairpin (~−1300 mV), compared to the Hx duplex (~−1360 mV), is the thermodynamically favored electron acceptor. The adsorption isotherms were constructed based on the voltammetric peak height values, reflecting the reduction of the adenine (A) and cytosine (C) moieties as well as the oxidation of the 7,8-dihydroguanine (7,8-DHG) moieties. Finally, as revealed by the spectroscopic and electrochemical results, Hx forms a bimolecular antiparallel homo-duplex carrying both Watson–Crick base pairs (CG or GC) and mismatched edge-to-edge base pairs (GA or AG).

Fast economic electrochemical assay for vitamins and heavy mineral components in honey samples of different botanical origin

Determination of heavy metals in honey samples is important as their presence indicates environmental contamination of the honey samples. The difficulty of such analysis is due to the complexity of the honey matrix because of the presence of natural honey nutrients as vitamins which can interfere in the analysis. A chemometric-based voltammetric method is used for the simultaneous estimation of some heavy metals and vitamins in different honey samples. The metals under investigation include: zinc, cadmium and lead, while the selected vitamins include: riboflavin (B2) and nicotininc acid (B3). The voltammetric analysis is fast and economic using simple inexpensive solvents and without any sophisticated sample pretreatment required. The chemometric handling is simply automated using Excel software®. The analysis is done in 0.1 M Potassium Chloride, KCl using hanging mercury drop electrode (HMDE), followed by chemometric handling of the obtained voltammetric data using first and second derivative. Then the derivative data are convoluted using 8-points sin xi polynomials (discrete Fourier functions). The proposed chemometric method facilitates the simultaneous determination of the selected metals and vitamins despite their variable responses, sensitivities and strong overlapping of their voltammetric peaks. Upon taking Zn, Pb and B3 as representative examples, their limit of quantitation (LOQ) and detection (LOD) values were greatly decreased after the chemometric treatment. The percentage decrease in their LOQ values compared to the direct method was 75%, 86% and 62% for Zn, Pb and B3, respectively. This method was successfully applied to analyze a complex mixture of some selected metals and vitamins in 12 honey samples of 6 different botanical origins without any matrix interference.

Electrochemical characterization of Cobalt(II)-Complexes involved in marine biogeochemical processes. I. Co(II)-4-nitrocatechol and Co(II)-Humate

Cobalt (II) as an important micronutrient for numerous biological processes in marine environment, has been tested in model aqueous solutions with naturally occurring ligands 4-nitrocatecol (4NC) and humic acid (HA) by voltammetry and spectrophotometry. Irreversible, two-electron reduction processes of Co(II)–4NC and Co(II)-HA complexes adsorbed on the mercury drop surface, depending on accumulation time and composition of the solution (cCo, c4NC,cHA and pH), were detected. Complexes Co:L = 1:1 stability constants formed only in the solution, were determined by spectrophotometry and amout to log KCo(II)4NC = 3.98 (pH = 8.2) and log KCo(II)4NC = 5.76 (pH = 6.5), and log KCo(II)HA = 3.80 (pH = 8.2). Co:L = 1:2 complexes Co(II)-(4NC)2 at pH 6.5 and 8.2 and Co(II)-(HA)2 at pH 8.2, formed at the mercury drop electrode surface as hydrophobic specia, were detected only by voltammetric measurements. Conditional stability constants were calculated by the CLE/ACSV method: log KCo(II) (4NC)2 = 21.86 (pH = 8.2), log KCo(II) (4NC)2 = 21.11 (pH = 6.5) and log KCo(II) (HA)2 = 11.32 (pH = 8.2).

2,2-Hydroxyphenylbenzoxazole as a selective chelating agent for complexation with Tin and Zinc: a voltammetry study

A highly selective and sensitive adsorptive stripping procedure for simultaneous determination of trace tin and zinc is presented. The method is based on adsorptive accumulation of the complexes of Sn (II) and Zn (II) ions with 2, 2-hydroxyphenylbenzoxazole (HBO) onto a hanging mercury drop electrode, followed by the reduction of the adsorbed species by differential pulse cathodic stripping voltammetry. The optimal experimental conditions include the use of 0.1 M acetate buffer (pH 5.0), 2.0×10-5 M HBO, an accumulation potential of -0.35 V (versus Ag/AgCl), an accumulation time of 90 s and a scan rate of 100 mV/s. Under optimised conditions, linear calibration curves were established for the concentration of Sn(II) and Zn(II) in the range of 0.2 -100 µg/L and 0.1- 120 µg/L, respectively, while the detection limit is 0.009 µg/L for tin and 0.01µg/L for zinc for a 90 s adsorption time. The method was applied to the determination of tin and zinc in biological samples with satisfactory results.

Catalytic and redox activity of nucleic acids at mercury electrodes: Roles of nucleobase residues

Using a series of specifically designed oligonucleotides we have identified adenine and cytosine nucleobases as residues involved in catalytic hydrogen evolution reaction (CHER) of nucleic acids at the hanging mercury drop electrode (HMDE). Due to the CHER, nucleic acids yield catalytic peak HNA allowing their label-free and reagent-less analysis at low concentrations. Additionally, our results suggest that presence of the electroactive bases (adenine and cytosine) facilitates guanine reduction which is for the first time linked to a signal measurable at the HMDE — the peak P. We assume that the peak P is connected with reduction of guanine to 7,8-dihydroguanine, of which reoxidation to guanine is detected at the electrode by the earlier described anodic peak G. Processes connected with the above mentioned signals were studied using cyclic voltammetry by inspection of dependences on experimental parameters such as negative vertex potential and pH.