Square-wave Adsorptive Stripping Voltammetry Research Articles

Electrochemical Properties and Determination of Serotonin with Graphene/Coal Tar Pitch/Pencil Graphite Sensor Electrode using Square Wave Adsorptive Stripping Voltammetry Technique

In the present work, electrochemical and spectroelectrochemical behaviors of Serotonin (5-HT) were studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. Cyclic voltammetric experiments of 5-HT on graphene/coal tar pitch/pencil graphite electrode (GR/CTP/PGE) were carried out between 0.0 V and 1.8 V potential range at a scan rate of 100 mV s-1 with 20 cycles in non-aqueous media. Surface characterizations were performed using CV, EIS and scanning electron microscope (SEM). Effect of different pH values was investigated by square wave voltammetry (SWV) for determination of 5-HT. Optimization of accumulation time was determined using square wave adsorptive stripping voltammetry (SWAdSV) within potential range of -0.2 to +0.6 V. 5-HT standard solutions changing from 75 µM to 1.0 µM were prepared and the corresponding peak currents were measured. From the obtained data calibration equation was derived Ip = 0.0329C5-HT + 0.1511 with correlation coefficient (R2) 0.9958. LOD was 3.51x10-7 M and LOQ was 1.05x10-6 M.

Investigation of Electrochemical Properties and Behaviors of NBITEP Molecule; Availability of Sensor Electrode in Determination of Hg2+ with SWAdSV Technique

This Master's Thesis focuses on the synthesis and structural elucidation of 4-(2-((6-nitro-1h-benzo[d]imidazol-2-yl)thio)ethyl)phenol (NBITEP) molecule, along with its electrochemical behaviors. Electrochemical studies were carried out employing a glassy carbon (GC) electrode as the working electrode. The cyclic voltammetry (CV) technique was utilized for modification and characterization processes. Furthermore, the potential of the modified surface as a sensor electrode for Hg2+ ion detection was investigated using square wave adsorptive stripping voltammetry (SWAdSV). Detailed examinations were conducted in a phosphate buffer solution (PBS) medium specifically for Hg2+ ion detection, demonstrating the suitability of the reduced NBITEP modified GC electrode surface as a sensor electrode.

Cobalt(II) bis-(1,10-phenanthroline) complex electropolymerized glassy carbon electrode and its electrocatalytic sensing of diclofenac in pharmaceuticals and biological samples

Diclofenac (DCF) is a nonsteroidal anti-inflammatory drug (NSAID) that is used to treat acute and chronic inflammatory diseases. High consumption and indiscriminate use of DCF pose serious health issues, prompting the consideration of electroanalytical methods for detecting and controlling DCF levels in various samples. A sensitive and highly selective sensor was established for voltammetric determination of diclofenac (DCF) based on poly[cobalt(II) bis-(1,10-phenanthroline) complex] modified glassy carbon electrode (poly(Co(Phen)2)/GCE). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the performance of a poly(Co(Phen)2)/GCE sensor, revealing a negative oxidation potential shift and higher DCF peaks of current. CV and adsorptive stripping square wave voltammetry (AdSSWV) were used to evaluate the electrochemical behavior of DCF at poly(Co(Phen)2)/GCE. Under the optimized experimental conditions, AdSSWV current signal of DCF at poly(Co(Phen)2)/GCE provided linearity over the range of 1–250 μM with a limit of detection (LOD) and limit of quantification (LOQ) of 6.40 ×10−2 and 2.13 ×10−1, and 5.60×10−2 and 2.27×10−1 µM for Ip I and Ip II, respectively. The sensor for determining DCF was tested in pharmaceuticals, milk, serum, and urine samples, demonstrating excellent selectivity despite potential interferences like atorvastatin (ATS), chloroquine (CQ), and sulfamethoxazole (SMX). The detected DCF amounts ranged between 92.3% and 106.6%. The established sensor demonstrated excellent performance in determining DCF in real samples, with spiked recoveries exceeding 95.6%, demonstrating low LOD, high sensitivity, selectivity, repeatability, and long-term stability. These results confirm that the established method displays outstanding applicability for electrochemical determination of DCF in numerous real samples.

Powerful Analytical Platform for Diazepam Determination in Pharmaceuticals and Alcoholic Drinks Based on Batch Injection Analysis Coupled with Adsorptive Stripping Voltammetry

The presented study focuses on the development and optimization of a powerful electroanalytical platform for the direct quantification of diazepam (DZP). This innovative approach integrates a batch injection analysis (BIA) system with a screen-printed electrode arrangement employing square-wave adsorptive stripping voltammetry (SWAdSV). The BIA-SWAdSV method underwent a comprehensive evaluation, wherein various experimental and instrumental parameters were systematically examined in detail. Beneficial analytical performance for detecting DZP was attained in Britton-Robinson buffer with pH 6.0, with an amplitude of 75 mV, a frequency of 10 Hz, a deposition potential of –1.2 V, a deposition time of 150 s, an injection volume of 75 μl, a dispensing rate of 7 μl s−1 and without stirring during the deposition step. Under these conditions, the proposed BIA-SWAdSV method demonstrated an adequately broad linear concentration range from 5 μM to 40 μM (R 2 = 0.997) with a micromolar limit of detection (2.0 μM) and a satisfactory precision (RSD = 5.0%). The practical applicability of the newly established and powerful analytical protocol was confirmed through the analysis of pharmaceuticals and a fortified samples of an alcoholic drink (rum) associated with potential criminal activities involving DZP abuse.

Fabrication of mesoporous carbon with a large surface area to achieve sensitive electrochemical sensing for nitazoxanide drug determination in human serum

Abstract Mesoporous carbon (MC) with a large surface area was developed to mix with the conventional carbon paste (CP) electrode. The developed MC/CP sensor had the highest sensitivity compared to many sensors made from other materials. A common drug, nitazoxanide (NTZ), was used as an application example. Using the MC/CP electrode and square wave-adsorptive stripping voltammetry (SW-AdSV), the concentration of NTZ in human serum was quantitatively estimated. We achieved a limit of quantification (LOQ) of 22 nM.

A simple electroanalytical methodology for determination of zaleplon by adsorptive stripping voltammetry in oral fluids

A glassy carbon electrode (GCE), modified with reduced graphene oxide (ErGO) (ErGO/GCE) was prepared for the determination of zaleplon, a common hypnotic pharmaceutical in synthetics and oral fluids. The modified electrode was evaluated using cyclic voltammetry, Raman spectroscopy, and scanning electrochemical microscopy (SECM). The electroanalytical studies were developed by square wave adsorptive stripping voltammetry (SW-AdSV) and parameters such as pH, accumulation potential, deposition time, and current response were optimized to determine zaleplon in Britton Robinson buffer. The validation was made using saliva-certified reference materials (Fusayama/Meyer Artificial Saliva and Artificial Saliva for Pharmaceutical Research showing good accuracy and reproducibility. The ErGO/GCE system showed a linear response between 10 and 130 µg/L at pH 10.0. The limit of detection was 5.30 μg L−1. The methodology was applied in the determination of zaleplon in saliva samples, obtaining excellent results (RSD < 10%), allowing the sensitive detection of zaleplon.

Utilizing epicatechin voltammetric oxidation signal for the estimation of total phenolic content in the tea samples via the unmodified boron-doped diamond electrode surface

In this work, the boron-doped diamond (BDD) electrode surface was employed for the first time in conjunction with the epicatechin (EC) oxidation signal to estimate the total phenolic content of tea samples by voltammetry. During cyclic voltammetry analysis of the EC, an easily identifiable, irreversible, and adsorption-controlled oxidation peak was observed at around +1.05 V (vs. Ag/AgCl) in HNO3 solution. Our experimental setup was fine-tuned by investigating the effect of electrode pretreatment, pH of the supporting electrolyte, accumulation factors, and instrumental parameters on the oxidation peak response of EC. When measuring EC in a 0.1 mol L−1 HNO3 solution at +1.0 V, square-wave adsorptive stripping voltammetry provided a highly linear response (at open-circuit accumulation for 30 s). The dynamic range was determined to be between 1.0 and 50.0 μg mL−1 (3.4510−6–1.7210−4 mol L−1), while the detection limit was found to be 0.28 μg mL−1 (9.6510−7 mol L−1). Selectivity studies were performed with other phenolic compounds found in tea such as epigallocatechin gallate, catechin, tannic acid, and gallic acid. Finally, by assessing the total phenolic content in the black and green tea samples, the suggested approach's applicability was shown by providing an estimate of the EC equivalents present in the samples.

The First Electroanalytical Study Of Umifenovir (Arbidol) Used As A Potential Antiviral Drug For The Treatment of SARS-CoV-2: A Voltammetric Quantification On The Boron-Doped Diamond Electrode By Using Anionic Surfactant Media

In this work, an electroanalytical procedure for sensing umifenovir (arbidol) by square wave adsorptive stripping voltammetry (SW-AdSV) was developed utilizing an anodically pretreated boron-doped diamond electrode. Measurements of umifenovir using cyclic voltammetry with phosphate buffer solution (PBS, 0.1 M, pH 2.5) revealed irreversible behaviour, adsorption-controlled as well as an ill-defined (+1.13 V, PA1) and a well-defined (+1.47 V, PA2) two oxidation peaks. Umifenovir oxidations depend critically on supporting electrolytes and pH. The second oxidation peak (PA2) current of the umifenovir was enhanced by adding sodium dodecyl sulfate (SDS, anionic surfactant) in the chosen supporting electrolyte. Umifenovir was quantified using its second oxidation peak (PA2) at about +1.39 V. Using the optimized condition, the oxidation peak current of PA2 showed a linear relationship for umifenovir determination in the concentration range from 0.005 to 1.0 μg ml−1 (9.73 × 10−9−1.95 × 10−6 M), with a detection limit of 0.0014 μg ml−1 (2.72 × 10−9 M) in PBS (PH 2.5) with SDS. Finally, the developed approach was successfully utilized to determine umifenovir in the pharmaceutical formulation and urine samples. To the best of our knowledge, this is the first electroanalytical approach for voltammetric sensing of umifenovir.

Glassy Carbon Modified with Cationic Surfactant (GCE/CTAB) as Electrode Material for Fast and Simple Analysis of the Arsenic Drug Roxarsone

For the fast and simple sensing of the arsenic drug roxarsone (ROX), the development of a glassy carbon electrode (GCE) modified with cationic surfactant (cetyltrimethylammonium bromide, CTAB) material is critical. The CTAB-modified glassy carbon electrode, in contrast to the unmodified one, showed excellent behavior for electrochemical reduction of ROX using cyclic voltammetry (CV) and square-wave adsorptive stripping voltammetry (SWAdSV) techniques. CV studies reveal an irreversible reduction process of NO2 to NH-OH in the ROX molecule in NaAc-HAc buffer (pH = 5.6). The electrode material was characterized using CV and electrochemical impedance spectroscopy. The experiments show that the surfactant-modified material has faster electron transfer and a higher active surface area, and permits a diffusion-adsorption-controlled process. After optimization, the SWAdSV procedure with GCE/CTAB has linear ranges of 0.001-0.02 and 0.02-20 µM, and a detection limit of 0.13 nM. Furthermore, the procedure successfully determined roxarsone in river water samples.

Voltammetric determination of anti-malarial drug amodiaquine at a boron-doped diamond electrode surface in an anionic surfactant media

In this study, the electrochemical determination of the amodiaquine (ADQ) drug was evaluated using an electrochemically pretreated boron-doped diamond (BDD) electrode due to the enhanced surface activity. The cyclic voltammogram results of ADQ were given as single reversible and diffusion-controlled peaks at +0.48 V for the oxidation peak and +0.05 V for the reduction peak (vs. Ag/AgCl) in Britton-Robinson (BR) buffer at pH 8.0. The peak potential and current signals of ADQ were evaluated at the surface of the BDD electrode using instrumental parameters to develop a simple method for ADQ detection. Also, the effect of an anionic surfactant, sodium dodecyl sulfate (SDS), on the adsorption applicability of the BDD electrode significantly increased the stripping voltammetric determination of ADQ. Under the optimal conditions chosen and employing square-wave adsorptive stripping voltammetry at the BDD electrode, ADQ was determined at + 0.34 V (vs. Ag/AgCl) at the open-circuit condition in BR buffer at pH 8.0 in the presence of 2·10–4 mol l–1 SDS. Furthermore, analytical parameters showed the linear relationship for ADQ determination in the concentration range of 0.1–20.0 μg ml–1 (2.2·10–7 – 4.3·10–5 mol l–1), with a detection limit of 0.03 μg ml–1 (6.5·10–8 mol l–1). The proposed approach can be applied to determine ADQ in water samples.

Fast and Simple Preparation of a Sensor Based on Electrochemically Reduced Graphene Oxide (rGO) for the Determination of Zopiclone in Pharmaceutical Dosage by Square Wave Adsorptive Stripping Voltammetry (SWAdSV)

AbstractThe interactions of zopiclone with electrochemically reduced graphene oxide (rGO) modified electrode were examined. A comparison of GC/rGO and glassy carbon electrode (GC) by electrochemical impedance spectroscopy and scanning electrochemical microscopy (SECM) shows that the modified surface is much less conductive than GC. The role of rGO is to act as a site of specific adsorption of the analyte. Molecular dynamics showed that the monoanionic form of zopiclone presents more interactions with defects of rGO. The analytical methodology allowed obtaining a linearity of 10–130 μg L−1, with a limit of detection of 2.14 μg L−1 using SWAdSV at pH 10.0.

An l-cysteic acid-modified screen-printed carbon electrode for methyl parathion determination

This work demonstrates the development and validation of a non-enzymatic sensor consisting of an l-cysteic acid-modified screen-printed carbon electrode (LCA-SPCE) sensor for the determination of the hazardous organophosphorus pesticide methyl parathion (MP) using square-wave adsorptive stripping voltammetry (SWAdSV). The surface of LCA-SPCE was investigated using time of flight secondary ion mass spectrometry to confirm successful preparation of the LCA surface layer. In order to obtain the highest electrochemical response, the accumulation time and pH of the 0.1 M phosphate buffer solution (PBS) supporting electrolyte were optimized. Then, SWAdSV method validation was performed in 0.1 M PBS at pH 6.00, an accumulation potential at the open circuit potential, and an accumulation time of 120 s. Since an intensive background was observed from the measurement of blank solution on the LCA-SPCE, a background subtraction procedure was employed. Partial method validation of the LCA-SPCE sensor was performed by determining the limit of detection (LOD), the limit of quantification (LOQ), the linear concentration range, accuracy, and precision. The developed method has a very low LOD and LOQ of 2.5 µg/L and 5.0 µg/L, respectively, and a linear concentration range of 5.0–84.3 µg/L (R2 = 0.9948). The average recovery and relative standard deviation were 109.6 % and 7.1 %, respectively (n = 6). This work also demonstrates the advantageous use of the multiple standard addition methodology compared to the calibration curve for analysing MP by means of an LCA-SPCE. Furthermore, electrochemical impedance spectroscopy was performed to show the differences between the bare-SPCE and LCA-SPCE. Finally, the application of the developed and validated LCA-SPCE sensor for the determination of MP was successfully employed for a real water sample (tap water), which showed the high accuracy and precision of the method. In addition, the interference and matrix effects were also studied.

On spot detection of nickel and cobalt from exhausted batteries by a smart electrochemical sensor

This work presents the realization and the application of an user-friendly electrochemical platform based on screen-printed electrodes for the simultaneous determination of nickel and cobalt ions in real samples by means of square wave adsorptive stripping voltammetry (SWAdSV). The sensor was realized by electrodepositing in situ a bismuth film onto graphite screen-printed electrodes (GSPEs). The sensor surface was fully characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS).The experimental conditions for the determination of nickel and cobalt in the form of dimethylglyoximate complexes were studied and optimized. Linear calibration curves for Ni(II) and Co(II), determined individually and together, in the range 10–40 μg/L for nickel and 10–60 μg/L for cobalt, respectively, were obtained. The limits of detection for nickel and cobalt determination were 2.5 μg/L and 2.4 μg/L, respectively. The performance of the sensor in terms of reproducibility and selectivity was also studied. The applicability of the developed platform was assessed by determining nickel and cobalt in samples deriving from an industrial process of recycling exhausted batteries and in soil samples.

Electrochemical study and forensic electroanalysis of fungicide benzovindiflupyr using disposable graphite pencil electrode

Nowadays, the use of pesticides in world agriculture is fundamental. However, it leads to an increase in the illegal sale and smuggling of these products in various parts of the world, mainly in Brazil. Therefore, the development of new analytical methods for screening and analysis of these kind of substances is a relevant issue. We present in this work, for the first time, an electrochemical study and a novel electroanalytical method for determination of fungicide benzovindiflupyr (BENZO). According to our knowledge, the electrochemical behavior of BENZO, as well as its voltammetric determination, have never been reported before. The sensors used here consisted of disposable pencil graphite electrodes (PGEs). On this electrode surface and at optimal pH, BENZO behaved according to a quasi-reversible system and showed two voltammetric peaks, one anodic at Ep = +0.59 V and another cathodic at Ep = +0.43 V. The analytical studies utilized BENZO anodic sweep and square-wave adsorptive stripping voltammetry (SWAdSV). All experimental and instrumental parameters were fully investigated and optimized. Under the best conditions, a calibration plot was obtained in the concentration range from 0.10 to 12.5 μmol L−1. The limits of detection (LOD) and quantification (LOQ) achieved were 0.023 and 0.076 μmol L−1, respectively. An electrochemical mechanism for BENZO oxidation was also proposed. The method developed here was successfully employed for the qualitative and quantitative forensic analysis of BENZO in smuggled products, showing good accuracy (recoveries ca. 104%) and precision (relative standard deviation < 5%). These data attest the potential for use of this method in forensic area.

Square wave-adsorptive stripping voltammetric technique development and validation for the determination of budesonide in pharmaceuticals and biological fluids using graphite working electrode

The cyclic voltammetry method was preliminarily used to study the reversibility nature of the electrochemical behaviour of budesonide (BDN) compound. The square wave-adsorptive stripping voltammetry (SW-AdSV) technique was applied to evaluate an electrochemical reduction of BDN in the phosphate buffer pH 2.5. The ultra-trace graphite working electrode was used to accumulate BDN onto its surface. An SW-AdSV reduction peak was observed in the potential of −0.98 V using Ag/AgCl reference electrode and Pt auxiliary electrode. Different parameters ,such as pH, buffer solutions, accumulations time and potential, frequency, amplitude and scan were investigated, and convection rates parameters were studied to acquire a high reduction response. The repeatability, stability, recovery, calibration curve and limit of detection and quantification parameters were studied to evaluate the analytical performance of the SW-AdSV technique. Repeatability and stability were monitored for 20 µM of BDN to give a 0.29% relative standard deviation (RSD%) that was achieved for five measurements and a very stable current for 120 min. The linearity was evaluated by studying the calibration curve over the range of 2 –25 µM (n = 8), given a linear relation between BDN concentrations and SW-AdSV signals. The limits of detection (LOD) and quantification (LOQ) were calculated to become 40 nM (0.017 ppm) and 0.134 µM (0.0577 ppm), respectively. The developed and validated method was successfully applied to the electrochemical study of BDN in pharmaceuticals and biological fluids.

First electrochemical study of a potent antifungal drug caspofungin: Application to its enhanced voltammetric sensing based on the performance of boron-doped diamond electrode in CTAB-mediated measurements

This present study describes the first electrochemical investigation of caspofungin, which is a semisynthetic echinocandin class of antifungal drug. For this purpose, an electrochemically pretreated (anodically and subsequently cathodically) boron-doped diamond (BDD) electrode was used. The cyclic voltammetric scans showed a single oxidation step that is irreversible and controlled by a dual mechanism of adsorption and diffusion. For the optimization of experimental conditions, the influence of the electrode pretreatment, pH of the supporting electrolyte, concentration of cationic surfactant cetyltrimethylammonium bromide (CTAB), accumulation variables, and instrumental parameters was examined on the current response of caspofungin. The improved sensitivity of the voltammetric measurements was observed due to the synergistic effect of CTAB on the adsorption capacity of BDD electrode in alkaline pH conditions. Employing square-wave adsorptive stripping voltammetry (using open-circuit accumulation for 60 s), the oxidation signal at around +0.45 V allowed to the determination of caspofungin in Britton-Robinson buffer at pH 11.0 containing 1 × 10−4 M CTAB. The process could be used in the concentration range from 2.06 × 10−7 to 1.03 × 10−5 M (from 0.25 to 12.5 μg mL−1 as acetate salt) with a detection limit of 5.27 × 10−8 M (0.064 μg mL−1 as acetate salt). A technique developed here was used successfully to determine caspofungin concentration in commercial parenteral dosage formulations.

Simple Voltammetric Determination of Iron in Ethanol and Biodiesel Using a Bismuth Film Coated Glassy Carbon Electrode

Square-wave adsorptive stripping voltammetry (SWAdSV) was used to determine iron in ethanol and biodiesel using a bismuth-film electrode (BiFE) prepared onto the surface of a glassy carbon electrode (GCE) by electrochemical deposition to promote the reduction of Fe (III) previously complexed with 1-(2-pyridylazo)-2-naphthol (PAN) directly in the electrochemical cell. The supporting electrolyte was composed by mixture of acetate buffer (0.1 mol L−1, pH 4.5) and ethanol (40/60% v/v) into which 500 µL of a 0.1 mmol L−1 stock solution of PAN was added as complexing agent. The Fe (III)-PAN complex presented a well-defined current peak at −0.7 V. For biodiesel, a treatment with tetramethylammonium hydroxide (TMAH) was proposed as an efficient mean to minimized matrix interferences. A limit of detection of 6.0 × 10−8 mol L−1 (0.06 µmol L−1) and limit of quantification of 2.0 × 10−7 mol L−1 (0.2 µmol L−1) were obtained for Fe(III). Under the optimized conditions, there were no significant interferences from Cu(II), Al(III), Mn(II), Cr(III), Cd(II), Zn(II) and Ni(II) and Pb(II) while Ni(II) interfered significantly. The analytical curves produced linear responses with equations I (µA) = (-1.315 × 10−7 ± 5.158 × 10−8) + (-0.238 ± 0.01) [Fe (III)] (µmol L−1), R2 = 0.992 and I (µA) = (-6.836 × 10−7 ± 1.124 × 10−8) + (-0.408 ± 0.013) [Fe (III)] (µmol L−1), R2=0.998 for pure ethanol and biodiesel, respectively. The method produced satisfactory results in quantifying original quantities of Fe(III) in fuel ethanol (5.65 ± 0.71 µmol L−1) and biodiesel (1.28 ± 0.25 µmol L−1) at a 95% confidence limit (n = 3).

Application of a Screen-Printed Sensor Modified with Carbon Nanofibers for the Voltammetric Analysis of an Anticancer Disubstituted Fused Triazinone.

In this paper, we propose the first analytical procedure—using a screen-printed carbon electrode modified with carbon nanofibers (SPCE/CNFs)—for the detection and quantitative determination of an electroactive disubstituted fused triazinone, namely 4-Cl-PIMT, which is a promising anticancer drug candidate. The electrochemical performances of the sensor were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and square-wave adsorptive stripping voltammetry (SWAdSV). The presence of carbon nanofibers on the sensor surface caused a decrease in charge-transfer resistance and an increase in the active surface compared to the bare SPCE. Under the optimised experimental conditions, the proposed voltammetric procedure possesses a good linear response for the determination of 4-Cl-PIMT in the two linear ranges of 0.5–10 nM and 10–100 nM. The low limits of detection and quantification were calculated at 0.099 and 0.33 nM, respectively. In addition, the sensor displays high reproducibility and repeatability, as well as good selectivity. The selectivity was improved through the use of a flow system and a short accumulation time. The SWAdSV procedure with SPCE/CNFs was applied to determine 4-Cl-PIMT in human serum samples. The SWAdSV results were compared to those obtained by the ultra-high-performance liquid chromatography coupled with electrospray ionization/single-quadrupole mass spectrometry (UHPLC-ESI-MS) method.

Analytical Comparison of Cefadroxil Determination by Square Wave Adsorptive Stripping Voltammetric and Spectrophotometric Methods

The goal of this research is to verify the proposed nano-silver amalgam paste electrode (Ag-nano-SPE) method to compare with a spectrophotometric technique based on derivatization with potassium periodate (KIO4 ), 2,4-dinitrophenyl hydrazine (DNP) and sodium hydroxide (NaOH) for the estimation of cefadroxil (CFDL) by square wave adsorptive stripping voltammetry (SWAV). The different parameters of both methods were optimized in detail separately and then compared their efficiency, selectivity, sensitivity and applications. The SWAV produced a reduction peak with a precise definition at -0.160 V while measuring CFDL in 0.04 molL-1 Britton–Robinson buffer at pH 4, accumulation potential (0.5 V), accumulation time (10 sec), and with stirring rate of 200 rpm. Whereas, the CFDL was measured at 515 nm (λmax) by UVVisible spectrophotometer after the derivatization by using 1.5 mL of 0.5 mM DNP, 1.5 mL of 6.52 mM KIO4 and 0.5 mL of 10 M NaOH solution at room temperature. The linear response for CFDL was found using the SWAV and spectrophotometric techniques along a linear dynamic range from 0.033 - 0.304 and 0.051 - 1.376 µM, respectively. However, the precision, detection limit and quantification limit of SWAV for CFDL in the samples and standards significantly lower (p &lt;0.01) as compared to spectrophotometric method. This indicates that the SWAV is more sensitive and selective than the spectrophotometric technique for regular CFDL analysis.

Bismuth-Chitosan Nanocomposite Sensors for Trace Level Detection of Ni(II) and Co(II) in Water Samples

Trace minerals play an essential role in methane production via anaerobic digestion (AD). It is important to monitor Ni(II) and Co(II) concentrations and the Ni/Co concentration ratio for the rapid diagnosis of the ecological status or activity of methanogens in AD. Electrochemical detection of Ni(II) and Co(II) was investigated by coating the Bi-chitosan nanocomposite on a glassy carbon electrode (GCE) via the electrodeposition technique. A square-wave adsorptive cathodic stripping voltammetry technique (SWAdCSV) was applied and optimized when dimethylglyoxime (DMG) was used as the chelating agent for Ni(II) and Co(II) measurements. The SWAdCSV results showed that the current peaks for Co(II) detection are 6.1 times greater than the current peaks for Ni(II) measurements, probably due to the different affinity of DMG molecules between Ni(II) and Co(II). DMG molecules demonstrated higher selectivity toward Co(II) cations compared to Ni(II). The modified Bi-chitosan GCE developed in this study showed a relatively wide range of the Ni(II) and Co(II) concentrations (2–100 µg L−1) with a limit of detection of 3.6 µg L−1 for Ni(II) and 2.4 µg L−1 for Co(II), respectively. The developed sensor was applied to Ni(II) and Co(II) spiked natural water samples and showed good performance of detection with 12 consecutive measurements. Overall, the fabricated sensor showed excellent sensitivity toward Ni(II) and Co(II) in natural water samples.