Adsorptive Voltammetry Research Articles

New polluting metals. Quantification in herbal medicines by voltammetric and spectroscopic analytical methods

A new application of voltammetric techniques in stripping mode to the quantitative determination of metals belonging to the platinum group (PGM) in herbal medicines, at the ultra-trace level, is reported. Pd (II), Pt (II) and Rh (III) are determined by means of square-wave adsorption voltammetry (SWAdSV); Os (VIII) and Ru (III) are determined through square-wave voltammetry in catalytic mode (SWCV); Ir (III) is determined through the application of square-wave catalytic voltammetry in adsorption mode (SWAdCSV). In all the applied methods, the voltammetric cell has the conventional setting with three-electrodes, which sees the presence of a suspended mercury-drop electrode (HMDE) or a glassy carbon electrode (GCE) as working electrodes for the determination of Ir (III). The auxiliary electrode was a platinum electrode, and an Ag∣AgCl∣KClsatd. electrode was employed as reference electrode.Validation of the analytical procedure here proposed has been achieved using reference standards: NIST-SRM 1570a (Spinach Leaves) and NIST-SRM 1573a (Tomato Leaves), both added with pure metal standards, obtaining satisfying precision values, better than the limits set for the validation of quantitative methods. Following the verification of the validity of the here presented procedure, commercially available herbal medicines, based on Eucalyptus globulus, Harpagophytum procumbens DC and Taraxacun officinale weber, were analyzed. Standard samples were also analyzed by atomic absorption spectroscopy, in order to have a reference technique for validating the entire procedure.

A simple, sensitive and efficient electrochemical platform based on carbon paste electrode modified with Fe3O4@MIP and graphene oxide for folic acid determination in different matrices

A new biomimetic sensor selective to folic acid based on a carbon paste modified with graphene oxide and Fe3O4 nanoparticles coated with molecularly imprinted polymer in the core@shell format (Fe3O4@MIPs) was obtained using the polyol method. The sensing phase was synthesized in a simple way and characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and Brunauer-Emmett-Teller (BET) surface area. In the binding experiments the selective material showed a high adsorption capacity (Q) of 30.4 mg g−1 for MMIP, while the Q value for MNIP (magnetic non-imprinted polymer) was 15.3 mg g−1 both of them following the Langmuir model to the adsorption procedure. After their efficiency was proven, these materials were used as modifiers in the electrochemical sensor (Fe3O4@MIP-GO/CPE). Under optimized conditions using the square-wave adsorptive voltammetry, the proposed sensor exhibited excellent response with a concentration linear range between 2.5 and 48 μmol L−1 and limit of detection of 0.65 μmol L−1 (S/σ = 3). The advantages obtained with the proposed method were high robustness, selectivity, and low cost being these characteristics due to the MIP; highly sensibility due to the high superficial area being the contribution of the magnetite in the core of material; and experimentally versatile since was possible carry out numerous reproductible analysis only make the renovation of the paste electrode surface by simple polishing. The sensor was applied successfully in pharmaceutical formulation and river water samples with recoveries percentages near 100%.

Square-Wave Adsorptive Cathodic Stripping Voltammetric Determination of Trace Palladium Using 4-(2-Thiazolylazo)-Resorcinol

A square-wave adsorptive cathodic striping voltammetry method has been established for trace determination of palladium. The method was based on the adsorptive enrichment of palladium(II)–4-(2-thiazolylazo)-resorcinol (TAR) complex at the hanging mercury drop electrode at pH 7–8 versus Ag/AgCl electrode. At the optimized stripping parameters of pH, scan rate, potential accumulation, deposition time, pulse amplitude, frequency, pulse width and TAR concentration, the established method exhibited good sensitivity and remarkable linear range of 0.5–53 µg/L for Pd. The limits of detection and quantification were 0.15 and 0.5 µg/L, respectively, with relative standard deviation of ±2.1% (n = 3) at 10 µg/L Pd. The developed method was judged by quantification of Pd in certified reference material (IAEA-Soil-7) and using inductively coupled plasma-mass spectrometry. The calculated Student t and F values did not exceed the tabulated t (2.18) and F (3.63) at P = 0.05, revealing no significant difference between the two methods. The method was free from the interference from most of the common anions, cations and surfactants present in water. The method was satisfactorily applied to the quantification of Pd in road dust and water samples.

Electrochemical determination of dinitramine in water samples using a pencil graphite electrode modified with poly-l-cystein-gold nanoparticle

In this work, the electrochemical determination of dinitramine was performed by adsorptive differential pulse voltammetry (AdDPV) as a sensitive method and using a pencil graphite electrode modified with poly-l-cystein-gold nanoparticles (PLC-AuNPs/PGE). The field emission scanning electron microscopy (FESEM), electrochemical impedance spectroscopy (EIS), and energy-dispersive X-ray spectroscopy (EDX) were used to investigate the electrochemical characteristics of the electrodes. After optimization of different parameters, including number of cycles and scan rate for polymerization of l-cystein and entrapment of AuNPs, pH, adsorptive time, adsorptive potential of dinitramine and step potential (Estep) in the AdDPV method, the signal of oxidation of dinitramine was obtained which linearity increased over the concentration range from 1.0 × 10–9 to 1.0 × 10–8 M and 1.0 × 10–8 to 5 × 10–6 M. The detection limit was obtained as 1.83 × 10–10 M and relative standard deviation was calculated as 2.5% for determination of 2.0 μM dinitramine. The proposed method was used to determine dinitramine in tap (drinking) and river waters. This was a new strategy with excellent sensitivity, reproducibility and stability to measure dinitramine.

Sensitive Quantification of Fe(III) in Food Samples at Screen Printed Carbon Electrode Modified with Graphene and Piroxicam by Catalytic Adsorptive Voltammetry

AbstractA new disposable sensitive voltammetric sensor for the determination of Fe(III) based on a graphene (G) and piroxicam (Pir) modified screen printed carbon electrode (Pir/G/SPCE) has been developed. The developed method is based on accumulation of Fe(III) on the surface of the prepared sensor strip, formation a complex with Pir and subsequent reduction the adsorbed chelated Fe(III) at −0.03 V (vs. Ag/AgCl) coupled with the catalytic enhancement of bromate. Characterizations of the modified electrode surface were performed by field emission scanning electron microscopy (FE‐SEM), energy dispersive X‐ray spectroscopy (EDX) and electrochemical impedance spectroscopy (EIS). Electrochemical behavior of the modified SPCEs was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Under the optimum conditions, the catalytic voltammetric method exhibited linear calibration plot in the concentration ranges of 1–100 ng mL−1 and 100–3500 ng mL−1 Fe(III) with a limit of detection of 0.3 ng mL−1. The sensor strip displayed good reproducibility with 1.7 % relative standard deviation (RSD%). The developed method was successfully applied for the determination of iron in food samples such as vegetables, fruit, and cereal.

Electrochemical determination of paracetamol in a pharmaceutical dose by adsorptive voltammetry with a carbon paste/La2O3 microcomposite.

This paper presents a new application for microcomposites based on carbon paste (CP) and La2O3 (LaOX). This simple and versatile microcomposite (LaOX/CPE) was applied toward the determination of paracetamol (PCM) through proton oxidation by square wave adsorptive voltammetry (SWAdV). The anodic peak current for PCM increased by nearly 70.0% compared with an unmodified CP, and the detection limit was 0.020 μmol L-1. The relative standard deviations (RSDs) were 1.0% (n = 7). The accuracy of the new method was evaluated with tap water spiked with known quantities of PCM, while ascorbic acid, caffeine, and acetylsalicylic acid were used for interference studies. Finally, the usefulness of the microcomposite was shown to have acceptable results when applied to detect and quantify PCM in various forms of a pharmaceutical dose, such as solid tablets, fruit-flavored powders for colds and syrups for children.

Nanohybrid carbon black-molybdenum disulfide transducers for preconcentration-free voltammetric detection of the olive oil o-diphenols hydroxytyrosol and oleuropein

A new hybrid nanomaterial is used in a screen-printed electrode (SPE) for sensing of the ortho-diphenols oleuropein (OLEU) and hydroxytyrosol (HYT) in extra virgin olive oil (EVOO) and related samples. The hybrid material consists of carbon black (CB) and molybdenum disulfide (MoS2). In comparison with individual nanomaterials, CB-MoS2 exhibits improved charge-transfer ability, low charge-transfer resistance, high electrical conductivity and enhanced electrocatalysis. The sensor is also characterized by (a) high sensitivity that avoids the need for adsorptive voltammetry, (b) reduced analysis time, and (c) high anti-fouling ability (electrode RSDOLEU < 8%, for n = 10). OLEU can be detected in the 0.3 to 30μM concentration range with a 0.1μM LOD, and HYT in the 2-100μM range with a 1μM LOD. A comparison of the data obtained by this sensor and by HPLC-UV exhibited high correlation (r = 0.995, p < 0.05). These data revealed the reliability of CB-MoS2 for analysis of complex EVOO and related samples. Graphical abstract CB-MoS2-based electrochemical sensor for fast and reliable assessment of total ortho-diphenols antioxidants in olive oils.

In vivo Hippocampal Serotonin Dynamics in Male and Female Mice: Determining Effects of Acute Escitalopram Using Fast Scan Cyclic Voltammetry.

Depression is a highly prevalent psychiatric disorder, impacting females at a rate roughly twice that of males. This disparity has become the focus of many studies which are working to determine if there are environmental or biological underpinnings to depression pathology. The biology of depression is not well understood, but experts agree that a key neurotransmitter of interest is serotonin. Most research on basic serotonin neurochemistry, by us and others, has predominantly focused on male models. Thus, it is now critical to include female models to decipher possible fundamental differences between the sexes that may underlie this disorder. In this paper, we seek to determine any such differences using fast-scan cyclic voltammetry (FSCV) and fast-scan controlled adsorption voltammetry. These techniques allow us to probe the serotonergic system via measurement of evoked and ambient serotonin at carbon fiber microelectrodes (CFMs). Our data reveal no statistical differences, in the hippocampus, in female serotonin chemistry during the different stages of the estrous cycle compared to the mean female response. Furthermore, no difference was observed in evoked serotonin release and reuptake, nor ambient extracellular serotonin levels between male and female mice. We applied a previously developed mathematical model that fits our serotonin signals as a function of several synaptic processes that control the extracellular levels of this transmitter. We used the model to study potential system differences between males and females. One hypothesis brought fourth, that female mice exhibit tighter autoreceptor control of serotonin, is validated via literature and methiothepin challenge. We postulate that this tight regulation may act as a control mechanism against changes in the serotonin signal mediated by estrogen spikes. Importantly, this safety mechanism has no consequence for acutely administered escitalopram’s (ESCIT’s) ability to increase extracellular serotonin between the sexes. This work demonstrates little fundamental differences in in vivo hippocampal serotonin between the sexes, bar control mechanisms in female mice that can be observed under extraneous circumstances. We thus highlight the importance of considering sex as a biological factor in determining pharmacodynamics for personalized medical treatments that involve targeting serotonin receptors.

Development of a microcomposite with single-walled carbon nanotubes and Nd2O3 for determination of paracetamol in pharmaceutical dosage by adsorptive voltammetry

This study presents for the first time a new composite of carbon paste (CP), single-walled carbon nanotubes (SWCNTs) and Nd2O3 (NdOX). This versatile composite (NdOX-SWCNT/CPE) was applied to the oxidation of paracetamol (PCM). The newly formed surface was characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The results showed greater conductivity and a higher surface area for the composite than those of the carbon paste alone. Moreover, the anodic peak currents for PCM increased from 1.6 to 3.6 µA with CPE and NdOX-SWCNT/CPE, indicating an increase of nearly 51.0% for the anodic peak current. On the other hand, the anodic peak potentials shifted from 0.67 to 0.57 V. The detection limits were 0.05 µmol/L with NdOX-SWCNT/CPE and 0.50 µmol/L with SWCNT/CPE. The relative standard deviations (RSDs) were 1.5% (n = 7). The accuracy and interference of the methods were evaluated with a urine chemistry control spiked with known quantities of PCM, uric acid, dopamine, ascorbic acid, caffeine, acetylsalicylic acid, tartrazine, sunset yellow, allure red, rutin, morin and metal ions. Finally, the novelty and usefulness of the composite were evaluated to quantify PCM in pharmaceutical dosage forms such as tablets, powders and syrups for children.

Determination of Tetracycline by Microdroplet Hydrodynamic Adsorptive Voltammetry Using a Multiwalled Carbon Nanotube Paste Rotating Disk Electrode

A novel and simple method is proposed for the determination of tetracycline by adsorptive voltammetry in a droplet using a carbon nanotube paste rotating disk electrode (CNTP-RDE). An enhanced electrochemical oxidation response of tetracycline was observed in pH 8.2 supporting electrolyte by the addition of a long-chain cationic surfactant, such as benzyldimethyltetradecylammonium chloride (zephiramine). Under the optimized experimental conditions, the calibration curve was linear across a tetracycline concentration range from 1.0 × 10−7 to 2.0 × 10−6 M. The limit of detection and sensitivity were 4.0 × 10−8 M and 0.9358 A M−1, respectively. This method was successfully employed for the determination of tetracycline in milk samples.

Cover Picture: Adsorptive Voltammetry for the Determination of Ochratoxin A Using Enrichment Effect by Cationic Surfactants (Electroanalysis 10/2018)

Cover Picture: Adsorptive Voltammetry for the Determination of Ochratoxin A Using Enrichment Effect by Cationic Surfactants (Electroanalysis 10/2018)

Adsorptive Voltammetry for the Determination of Ochratoxin A Using Enrichment Effect by Cationic Surfactants

AbstractA rapid and simple electrochemical method was utilized for the determination of the presence of classic fungal metabolite ochratoxin A (OTA) based on differential pulse adsorptive voltammetry, using the carbon nanotube paste (CNTP) electrode. OTA showed a clear oxidation peak, and the CNTP electrode exhibited a more sensitive response to OTA oxidation than the glassy carbon, the plastic formed carbon, and the carbon paste electrodes. The addition of long‐chain cationic surfactants, such as benzethonium chloride, cetyltrimethylammonium bromide, and benzyldimethyltetradecylammonium chloride (zephiramine), enhanced the electrochemical response of OTA. Under optimized experimental conditions, the calibration plots are linear in the 5×10−6−5×10−5 M OTA concentration range, and the limit of detection is 1.1×10−6 M. In order to improve the selectivity for OTA determination, we attempted to combine this adsorptive stripping voltammetric technique with “sequestration electrochemistry,” based on the specific interaction occurring between bovine serum albumin (BSA) and OTA. The peak current of OTA oxidation decreased substantially as a result of OTA‐BSA binding. Furthermore, it was demonstrated that the application of this proposed method of hydrodynamic adsorptive voltammetry, using a micro‐droplet and a rotating disk electrode, improves the approach's sensitivity and reduces the time and sample volume required for the analysis.

Detection of Sunset Yellow by Adsorption Voltammetry at Glassy Carbon Electrode Modified with Chitosan

Detection of Sunset Yellow by Adsorption Voltammetry at Glassy Carbon Electrode Modified with Chitosan

Speciation of morin and rutin in black tea,Cymbopogon citratusand fruit infusions by adsorption voltammetry using screen-printed carbon electrodes coated with chitosan: effect of pH on speciation

This paper presents the versatility of chitosan in the preparation of modified electrodes without the use of other substances.

Adsorptive Stripping Voltammetric Determination of Amaranth and Tartrazine in Drinks and Gelatins Using a Screen-Printed Carbon Electrode.

A fast, sensitive, and selective method for the simultaneous determination of one pair of synthetic colorants commonly found mixed in food products, Amaranth (AM) and Tartrazine (TZ), based on their adsorption and oxidation on a screen-printed electrode (SPE) is presented. The variation of peak current with pH, supporting electrolyte, adsorption time, and adsorption potential were optimized using square wave adsorptive voltammetry. The optimal conditions were found to be: pH 3.2 (PBS), Eads 0.00 V, and tads 30 s. Under these conditions, the AM and TZ signals were observed at 0.56 and 0.74 V, respectively. A linear response were found over the 0.15 to 1.20 µmol L−1 and 0.15 to 0.80 µmol L−1 concentrations, with detection limits (3σ/slope) of 26 and 70 nmol L−1 for AM and TZ, respectively. Reproducibility for 17.7 µmol L–1 AM and TZ solutions were 2.5 and 3.0% (n = 7), respectively, using three different electrodes. The method was validated by determining AM and TZ in spiked tap water and unflavored gelatin spiked with AM and TZ. Because a beverage containing both AM and TZ was not found, the method was applied to the determination of AM in a kola soft drink and TZ in an orange jelly and a soft drink powder.

Evaluation of the usefulness of a novel electrochemical sensor in detecting uric acid and dopamine in the presence of ascorbic acid using a screen-printed carbon electrode modified with single walled carbon nanotubes and ionic liquids

A novel sensor was developed in order to determine dopamine (DP) and uric acid (UA) by adsorptive voltammetry, using optimal amounts of single walled carbon nanotubes (SWCNT) dispersed in chitosan solution (cs) and deposited on a screen-printed carbon electrode (SPCE). The electrode surface (cs-SWCNT/SPCE) was treated with the ionic liquid (IL) 1 butyl-3-metilimidazolium tetrafluorborate (BMIMBP4). The electro-catalytic properties of the cs-SWCNT-IL/SPCE were studied with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electrode surface was studied using scanning electron microscopy (SEM). Anodic peak currents for DP and UA with BMIMBP4 in the presence of ascorbic acid (AA) increased by 17.0 and 70.0% respectively. Optimal parameters were (pH 2.4; adsorption time; tADS 100s and adsorption potential; EADS -0.10 V). Anodic peak currents were proportional to the concentration between 0.5 and 5.0 μmol L−1 using standard solutions of PD and UA respectively, and 0.50–30.0 μmol L−1 for DP and 0.50–1000 μmol L−1 for UA with real samples. Detection limits were 0.16 μmol L−1 for DP and 0.17 μmol L−1 for UA. The sensor was used in the determination of AU and DP in human urine samples spiked with quantities of DP with recovery between 85 and 102% for DA and UA respectively.

In Vivo Ambient Serotonin Measurements at Carbon-Fiber Microelectrodes.

The mechanisms that control extracellular serotonin levels in vivo are not well-defined. This shortcoming makes it very challenging to diagnose and treat the many psychiatric disorders in which serotonin is implicated. Fast-scan cyclic voltammetry (FSCV) can measure rapid serotonin release and reuptake events but cannot report critically important ambient serotonin levels. In this Article, we use fast-scan controlled adsorption voltammetry (FSCAV), to measure serotonin's steady-state, extracellular chemistry. We characterize the "Jackson" voltammetric waveform for FSCAV and show highly stable, selective, and sensitive ambient serotonin measurements in vitro. In vivo, we report basal serotonin levels in the CA2 region of the hippocampus as 64.9 ± 2.3 nM (n = 15 mice, weighted average ± standard error). We electrochemically and pharmacologically verify the selectivity of the serotonin signal. Finally, we develop a statistical model that incorporates the uncertainty in in vivo measurements, in addition to electrode variability, to more critically analyze the time course of pharmacological data. Our novel method is a uniquely powerful analysis tool that can provide deeper insights into the mechanisms that control serotonin's extracellular levels.

Improved electroanalytical characteristics for flumetralin determination in the presence of surface active compound

The use of square wave voltammetry (SWV) and square wave adsorptive stripping voltammetry (SWAdSV) in conjunction with a cyclic renewable silver amalgam film electrode for the determination of flumetralin is presented. Poor separation of two overlapped reduction peaks is significantly improved when hexadecyltrimethylammonium bromide is used as a component of the supporting electrolyte solution (together with BR buffer pH 9.5). The SW technique parameters were investigated and found optimal as follows: frequency 50 Hz, amplitude 40 mV, and step potential 5 mV. Accumulation time and potential were studied to select the optimal conditions in adsorptive voltammetry. The analytical curve was linear for the flumetralin concentration range from 1.0 × 10−6 to 1.0 × 10−5 mol dm−3 and from 5.0 × 10−9 to 1.0 × 10−7 mol dm−3 for SWV and SWAdSV, respectively. Detection limit of 6.5 × 10−10 mol dm−3 was calculated for accumulation time 60 s at −0.2 V. The repeatability of the method was determined at a flumetralin concentration level equal to 5.0 × 10−9 mol dm−3 and expressed as %RSD = 5.0% (n = 6). The proposed method was applied and validated successfully by studying the recovery of herbicide content in spiked environmental samples.Graphical abstract

Development of an Electrochemical Sensor to Detect Dopamine and Ascorbic Acid Based on Neodymium (III) Oxide and Chitosan

AbstractNeodymium (III) oxide (NdOx) was dispersed in chitosan dissolution and deposited on a glassy carbon electrode (chitosan‐NdOx/GCE). The surface properties of the chitosan‐NdOx/GCE were evaluated with FeCN6−3 solution using cyclic voltammetry and electrochemical impedance spectroscopy. The modified electrode was used in the determination of individual dopamine (DP) and ascorbic acid (AA) with square wave adsorptive voltammetry. Under optimal parameters (pH 4.0; accumulation time; tACC 60s and accumulation potential; EACC 0.10 V) for DP and (pH 3,0; tACC 60s and; EACC −0.20 V) for AA, anodic peak currents were proportional to the concentration of DP and AA between 0.90 and 17.0 μmolL−1, with detection limit of 0.079 μmolL−1 for DP and 0.12 μmolL−1 for AA. The sensor was used in the determination of DP and AA in human urine samples and vitamin C tablets with consistent results. The new sensor is easy to develop. In addition, the sensitivity in particular for AA was improved compared with previous work.

Significance of Mesoporous Electrodes for Noncatalytic Faradaic Process of Randomly Oriented Redox Proteins

To investigate the effect of mesoporous media as electrodes for the observation of a noncatalytic Faradaic current of redox proteins adsorbed on an electrode (i.e., redox peaks in adsorption voltammetry), we propose a simulation model with randomly oriented redox proteins to obtain adsorption voltammograms. Furthermore, we compare the simulated currents of redox proteins adsorbed on planar and mesoporous electrodes. In this model, a redox protein is postulated as a sphere with the active site located at a certain distance from the center of the protein. For a mesoporous electrode, a spherical pore with a radius of Rp is assumed. When Rp is close to the radius of the protein, a redox peak is obtained even when the active site is located at a great distance from the protein surface; however, the peak is not observed for a planar electrode. This is ascribed to an increase in the number of proteins with orientations suitable for electron transfer because of the curvature effect of the pore. This work indicate...