Square-wave Stripping Voltammetry Research Articles

A new strategy for the determination of dinobuton fungicide by square wave stripping voltammetry on the multi-walled carbon nanotube electrode

Dinobuton is a fungicide with a dinitrophenol group pesticide, and its electrochemical behavior was investigated by cyclic voltammetry (CV) and square wave stripping voltammetry (SWSV) on a multi-walled carbon nanotube paste electrode (MWCNTPE). First of all, optimum parameters such as pH, step potential, frequency, puls amplitude, deposition time and, deposition potential were specified by using SWSV on the MWCNTPE. In the negative potential scans, two cathodic peaks appeared at nearly −480 mV and –760 mV due to the nitro groups on the molecule and the second sharp one appeared at −760 mV (versus Ag/AgCl) was used for analytical purposes. The linear working range was found to be within 3.74–25.8 μM on the MWCNTPE by SWSV in pH 7.0 Britton Robinson (BR) buffer solution. The limit of detection (LOD) and limit of quantification (LOQ) values were found to be 0.73 μM and 2.43 μM, respectively. The interference study was conducted in the presence of some pesticides such as triasulfuron, azinphos-methyl, bromoxynil-octanoate, dialifos, fipronil, vinclozolin, iprodione, procymidone, and some selected metal ions withal. Furthermore, the proposed method was also applied to apple juice, tap water, and grape juice, and percent recoveries (%) were detected as 105.9 ± 4.3; 98.3 ± 0.9; 103.7 ± 2.5% with relative standard deviations of 4.0, 1.0, and 2.4%, respectively. On the other hand, percent relative errors were calculated as 5.90, 1.65, and 3.74%, respectively. High recoveries and low relative standard deviations indicate that the applicability of the proposed method in both matrix and real samples is satisfying.

Iron oxide-supported gold nanoparticle electrode for simultaneous detection of arsenic and sulfide on-site

The environmental behavior of arsenic (As) has garnered significant attention due to its hazardous nature. The fate of As often couples with sulfide, thus co-detecting arsenic and sulfide on-site is crucial for comprehending their geochemical interactions. While electrochemical methods are suitable for on-site chemical analysis, there currently exists no electrode capable of simultaneously detecting both arsenic and sulfide. To address this, we developed a dual-metal electrode consisting of iron oxide-encased carbon cloth loaded with gold nanoparticles (Au/FeOx/CC) using the electrochemical deposition method. This electrode enables square wave stripping voltammetry (SWASV) binary detection of As and sulfide. Comparison experiments reveal that the reaction sites for sulfide primarily reside on FeOx, while the interface synergy of iron oxide and gold nanoparticles enhances the response to arsenite (AsIII). Arsenate (AsV) is directly reduced to As0 on Fe0, obviating the need for an external reducing agent. The electrode achieves detection limits of 1.5 μg/L for AsV, 0.25 μg/L for AsIII, and 11.6 μg/L for sulfide at mild conditions (pH 7.8). Field validation was conducted in the Tengchong geothermal hot spring region, where the electrochemical method exhibited good correlation with the standard methods: Total As (r = 0.978 vs. ICP-MS), AsIII (r = 0.895 vs. HPLC-ICP-MS), and sulfide (r = 0.983 vs. colorimetric method). Principal component analysis and correlation analysis suggest that thioarsenic, could potentially be positive interferents for AsIII. However, this interference can be anticipated and mitigated by monitoring the abundance of sulfide. The study provides new insights and problems for the electrochemical detection of coexisted As and sulfide.

Simultaneous voltammetric determination of acetylsalicylic acid, caffeine and paracetamol in pharmaceutical formulations using screen‐printed carbon electrode

AbstractElectrochemical oxidation of Paracetamol (PAR), Acetylsalicylic acid (ASA) and Caffeine (CAF) was investigated employing square wave stripping voltammetry (SWSV) using screen–printed carbon electrodes (SPCE). Determinations were performed in 0.1 mol L−1 BR buffer (pH 2.0) without accumulation step. SWV were obtained by scanning the potential from 0.00 to 1.40 V employing a scan increment of 4 mV, pulse amplitude 25 mV and frequency of 25 Hz. PAR, ASA and CAF presents oxidation signals at 0.45, 1.03 and 1.32 V. The detection limits were 1.2, 1.7 and 1.7 mg L−1, respectively. The method was applied in the PAR‐ASA‐CAF determination on pharmaceutical formulations.

Heteroatom engineered graphene-based electrochemical assay for the quantification of high-risk abused drug oxytocin in edibles and biological samples

The naive detection of scheduled H drug oxytocin is a vital requisite, owing to its deleterious impact on societal affluence prompted by unconstrained usage. Therefore, a reliable, cost-effective, and quick-to-respond analytic technique for this drug is in ample demand. In this work, we report electrochemical detection of oxytocin employing novel nitrogen, phosphorus co-doped coke-derived graphene (NPG) modified electrode. The electro-oxidation behavior of oxytocin was investigated on the NPG modified electrode by square wave stripping voltammetry (SWSV) in 0.1 M phosphate buffer of pH 7. The oxidation peak current was linear in two ranges, spanning from 0.1 nM to 10 nM and 15 nM to 95 nM. The limit of detection at the NPG electrode was calculated to be 40 pM. The practical application of developed sensor for the determination of oxytocin was examined in edible products and body fluids, hence signifying the possibility of having real-time surveillance over its misusage.

Preparation of a polyurethane membrane testosterone sensor and its application using square-wave stripping voltammetry

A novel electrochemical sensor for testosterone detection has been prepared by the chemical modification of a gold electrode (AuE). For the electrode modification, specific polyurethane (PU) films were synthesized from hexamethylene diisocyanate, olivetol, polyethylene glycol-100 (PEG100) and β-cyclodextrin. The synthesized PUs were investigated as selective films, and were used to coat a AuE surface at different concentrations and thicknesses. The testosterone responses of the modified electrodes were investigated by square-wave voltammetry (SWV). One separated cathodic SWV peak was obtained for testosterone at –0.390 V, with the prepared PU-modified AuE in 0.1 M phosphate buffer (PB) (pH 7.2). The linearity of testosterone responses of the prepared PU modified electrode was obtained over a concentration range of 0.1–1.0 µM (R2 = 0.995). It was observed that the response of the electrode increased regularly and sensitively with increasing testosterone amount. The detection limit, relative standard deviation and sensitivity of modified electrode were found to be approximately 5.69 nM, 1.669 % and 98.331 %, respectively. The PU-modified AuE exhibited good selectivity and a low response time for testosterone. Therefore, the prepared testosterone sensor offers a good alternative for fast and practical testosterone determination in clinical or biomedical studies.

Trace assay of insulin in a pharmacy drug with a paste electrode.

This paper describes the development of a voltammetric assay of insulin using a DNA immobilized onto a carbon nanotube paste electrode (CNPE), the peak potential of which was 0.2V, vs. Ag/AgCl on the CNPE. The cyclic voltammetry (CV) and square-wave (SW) stripping voltammetry parameters of the optimized conditions were determined. Low analytical working ranges of 10-80 ugL-1 CV and 0.01-0.1 ngL-1 SW were attained. The precision of the insulin concentration of 0.01 ugL-1 was 0.14 (n = 15) RSD using the optimum conditions, in which the detection limit was 0.004 ngL-1 (6.9 × 10-12M) (S/N = 3) using only an accumulation time of 400s. The developed method was applied to determine insulin in a pharmacy drug from analytical-grade chemicals (from Aldrich).

Use of electrochemical methods to determine the effect of brewing techniques (Espresso, Turkish and Filter coffee) and roasting levels on the antioxidant capacity of coffee beverage.

Coffee is a complex mixture of chemicals, which provide biologically active compounds with various health benefits. The some biologically active compounds arising from both its natural structure and formed after processing were determined as an antioxidant capacity of coffee beverages. In this study, we aimed to determine how roasting levels of Arabica coffee seed (light, medium, dark) and three brewing techniques-decoction methods (Turkish coffee), infusion method (filter coffee) and pressure methods (Espresso)-affect total antioxidant capacity in a cup of coffee beverage by electrochemical methods such as square wave stripping voltammetry (SWSV), differential pulse stripping voltammetry (DPSV) and cyclic voltammetry (CV). Antioxidant capacities of the coffee samples in terms of the equivalent amounts were determined according to standard oxidation peaks of rutin and caffeic acid. The highest antioxidant capacity was found in espresso coffee prepared at light roasting coffee seeds as equivalent the routine and caffeic at 9.4 ± 0.2g/L and 19.7 ± 0.7g/L, respectively with SWSV on a carbon paste electrode. As a result, SWSV, DPSV and CV voltammetric methods, fast, reliable, fully validated and without any pretreatment are alternative to conventional analytical methods to evaluation antioxidant values in any food samples.

Use of electrochemical techniques for determining the effect of brewing techniques (espresso, Turkish and filter coffee) and roasting levels on total antioxidant capacity of coffee beverage

In this study, we determined how roasting levels (light, medium, and dark) of Arabica coffee seed and three brewing techniques—decoction methods (Turkish coffee), infusion method (filter coffee), and pressure methods (Espresso)—affect the total antioxidant capacity in a cup of coffee beverage by electrochemical methods such as square wave stripping voltammetry (SWSV), differential pulse stripping voltammetry (DPSV), and cyclic voltammetry (CV). The highest antioxidant capacity was found in espresso coffee prepared with light roasted coffee seeds, as equivalent of rutin and caffeic acid at 9.4 ± 0.2 g/L and 19.7 ± 0.7 g/L, respectively with SWSV on a carbon paste electrode (CPE). The antioxidant capacity of coffee beverages was influenced by the roasting degree, extraction time, and brewing methods, significantly. SWSV, DPSV, and CV voltammetric methods, fast, reliable, fully validated and without any pretreatment, are alternatives to conventional analytical methods for evaluation of antioxidant values in coffee brews. Practical applications This research will contribute to the literature considerably since we have established that the antioxidant capacity can be measured by electrochemical methods rapidly with high reliable results. According to the study, the brewing method and roasting temperature significantly affected the antioxidant capacity, and thus, it is important to know how brewing methods, roasting temperatures, and other conditions changes the coffee quality. The results can be used to prepare healthy coffee beverages.

A flexible and disposable electrochemical sensor for the evaluation of arsenic levels: A new and efficient method for the batch fabrication of chemically modified electrodes

In this study, a novel flexible and disposable electrochemical sensor was fabricated through the straightforward laser-induced synthesis of catalytic Au nanoparticles (AuNPs)@LIG composite for the square wave stripping voltammetry (SWASV) determination of arsenic in soil. In this process, polyimide and a metal precursor (PI-MP) were transformed to three-dimensional porous LIG and AuNPs through the graphitization, photoreduction and thermal reduction of laser ablation. To our knowledge, this is the first time that laser-induced PI-MP was employed to fabricate chemically modified electrodes on a large scale for arsenic determination. X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectrometer (EDX), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and N2 adsorption isotherm were used to characterize the morphological and physical properties of the materials, which demonstrated the successful synthesis of AuNPs@LIG nanocomposite. Additionally, the mechanism of AuNPs@LIG synthesis by laser induction was also investigated, and the deposition potential and the deposition time for the SWASV determination of arsenic were also optimized. The electrochemical sensor fabricated using the proposed method shows satisfactory sensitivity, stability and reliability and exhibits a good linear relationship over concentrations ranging from 0 to 40 μg/L, with a low determination limit of 0.18 μg/L. Furthermore, the obtained AuNPs@LIG surface exhibited good conductivity with a charge transfer resistance (Rct) of 73.85 Ω and a large real surface area of 807.28 mm2. Finally, several real soil samples were analyzed using the prepared sensor with a satisfactory result, which verified the feasibility of this sensor. The results show that the method for chemically modified electrode fabrication proposed in this paper has good commercial potential for the batch manufacturing of electrochemical sensors.

Development and characterization of iron (III) phthalocyanine modified carbon nanotube paste electrodes and application for determination of fluometuron herbicide as an electrochemical sensor

This study is the first electroanalytical study conducted for the determination of fluometuron herbicide. For this purpose, a new electrode was prepared by combining iron (III) phthalocyanine − 4.4′,4′′,4′′′-tetrasulfonic acid, oxygen monosodium salt hydrated compound (FePc) and multi-walled carbon nanotube powders (MWCNTP). The FePc/MWCNTP composite (hybrid) material prepared in this way was coated on glassy carbon electrode (GCE) and multi-walled carbon nanotube paste electrode (MWCNTPE) using the drop-dry method. Compared to both the bare GCE and MWCNTPE, the modified FePc/MWCNTPE increased the anodic peak current of fluometuron by approximately six fold. Calibration plots of the fluometuron were constructed using the standard addition method with differential puls stripping voltammetry (DPSV) and square wave stripping voltammetry (SWSV) under the optimum conditions. While the working range was determined as 0.4–15.0 mg/L in pH 6.0 Britton Robinson (BR) buffer solution on FePc/MWCNTP electrode with DPSV, this range was found to be 0.4–7.5 mg/L with SWSV. In addition, the limit of detection (LOD) and the limit of quantification (LOQ) values ​​were 69.8 µg/L and 233.0 µg/L, respectively, by DPSV. On the other hand, these two validation values ​​(LOD and LOQ) were 101 µg/L and 337 µg/L by SWSV, respectively. Subsequently, cyclic voltammetric (CV) studies were carried out to elucidate the electrochemical behavior and electrode mechanism of the fluometuron herbicide. In addition, the interference effects of some cations and pesticides in the determination of fluometuron were examined. Finally, studies of recovery of fluometuron herbicide from tap water and determination of fluometuron in Cottonex 500 SC® commercial pesticide formulation using the proposed DPSV method and modified FePc/MWCNTP electrode were performed with very low relative error.

The construction of CoP nanoparticles coated with carbon layers derived from core-shell bimetallic MOF for electrochemical detection of dopamine

Design of catalysts with unique structures in enhancing electrochemical activity and stability has still been pursued. An eco-friendly method for preparing CoP with improved electrochemical performances was proposed in this work. A novel P-doped bimetallic ZIF-67@ZIF-8 (ZIF-67@ZIF-8-P) was prepared as the precursor for constructing of CoP@C/NCS, in which CoP nanospheres coated with carbon layers (CoP@C for short) were well-dispersed on N-doped carbon spheres (NCS for short). P was strategically pre-introduced into ZIF-67@ZIF-8 for preparing of ZIF-67@ZIF-8-P through the selective phosphorylation on ZIF-8 shell. DA was selected to investigate the electrochemical properties of CoP@C/NCS. Glassy carbon electrode (GCE) modified by CoP@C/NCS exhibited excellent properties in detection of DA by square wave stripping voltammetry (SWV), that a high sensitivity of 9.4 μA μM−1, and low limit of detection of 0.03 μM. In addition, CoP@C/NCS showed enhanced performances on electrocatalytic oxidation of DA than that of CoP/C prepared based on ZIF-67 by the common phosphorization method reported in literatures. Moreover, a wide linear range from 5.0 μM to 400.0 μM was achieved at CoP@C/NCS/GCE by amperometric i-t. The practical application of CoP/NCS/GCE was evaluated by detection of DA in human serum. The satisfactory recoveries in diluted serum demonstrated the promising application of CoP@C/NCS.

A composite prepared from covalent organic framework and gold nanoparticles for the electrochemical determination of enrofloxacin

A high conductivity composite based on covalent organic frameworks/gold nanoparticles (TAPB-PDA-COFs/AuNPs, TAPB: 3,5-tris(4-aminophenyl)benzene, PDA: p-phthalaldehyde) was prepared by a simple in-situ synthesized method and a novel electrochemical sensor based on TAPB-PDA-COFs/AuNPs was constructed for detection of Enrofloxacin (ENR). A variety of different characterization techniques including ultraviolet‐visible spectrophotometer (UV–vis), fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the TAPB-PDA-COFs/AuNPs. ENR was detected by square wave stripping voltammetry (SWV) according to the relationship between the ENR concentration and the oxidation peak current. The result showed that TAPB-PDA-COFs/AuNPs was synthesized successfully. The electrochemical sensor showed two linear ranges in the range of 0.05–10 μmol L−1 and 10–120 μmol L−1 with the limit of detection of 0.041 μmol L−1 (S/N = 3). The good recoveries (96.7–102.2%) and low RSDs (0.9–6.4%) indicated the possibility of using this sensor for actual sample detection. Therefore, TAPB-PDA-COFs/AuNPs-based electrochemical sensor showed good performance in detecting ENR, and would be a potential candidate for the development of fluoroquinolones determination.

Preparation of GO/Fe3O4@PMDA/AuNPs nanocomposite for simultaneous determination of As3+ and Cu2+ by stripping voltammetry

One of the critical challenges in the simultaneous determination of As3+ and Cu2+ by stripping voltammetry is the overlapping of their oxidation peaks. Therefore, the engineering of nanostructured sensors in order to uplift their electrochemical performance is a significant issue for the codetection of As3+ and Cu2+. Herein, we modified a glassy carbon electrode with a new nanocomposite based on poly methyldopa along with gold nanoparticles immobilized on the surface of magnetic graphene oxide (GCE/GO/Fe3O4@PMDA/AuNPs) that can determine As3+ and Cu2+ with great sensitivity. Optimization of the measurement conditions by square wave stripping voltammetry (SWSV) caused the oxidation peaks of As3+ and Cu2+ to be distinguished significantly from each other, while the peak currents of As3+ and Cu2+ increased 9–12 fold, respectively, compared to the bare electrode. The proposed electrode exhibits low detection limits (S/N ≥ 3): 0.15 ppb for As3+ and 0.11 ppb for Cu2+. The GCE/GO/Fe3O4@PMDA/AuNPs also has good linearity over a wide concentration range from 5 to 500 ppb for As3+ and 0.5–750 ppb for Cu2+. The good recovery values were obtained for the analysis of As3+ and Cu2+ in pool and drinking water samples.

Parts per trillion detection of heavy metals in as-is tap water using carbon nanotube microelectrodes

Heavy metal contamination of drinking water is a major global issue. Research reports across the globe show contamination of heavy metals higher than the set standards of the World Health Organization (WHO) and US Environmental Protection Agency (EPA). To our knowledge, no electrochemical sensor for heavy metals with parts per trillion (PPT) limits of detection (LOD) in as-is tap water has been reported or developed. Here, we report a microelectrode that consists of six highly densified carbon nanotube fiber (HD-CNTf) cross sections called rods (diameter ∼69 μm and length ∼40 μm) in a single platform for the ultra-sensitive detection of heavy metals in tap water and simulated drinking water. The HD-CNTf rods microelectrode was evaluated for the individual and simultaneous determination of trace level of heavy metal ions i.e. Cu2+, Pb2+ and Cd2+ in Cincinnati tap water (without supporting electrolyte) and simulated drinking water using square wave stripping voltammetry (SWSV). The microsensor exhibited a broad linear detection range with an excellent limit of detection for individual Cu2+, Pb2+ and Cd2+ of 6.0 nM, (376 ppt), 0.45 nM (92 ppt) and 0.24 nM (27 ppt) in tap water and 0.32 nM (20 ppt), 0.26 nM (55 ppt) and 0.25 nM (28 ppt) in simulated drinking water, respectively. The microelectrode was shown to detect Pb2+ ions well below the WHO and EPA limits in a broad range of water quality conditions reported for temperature and conductivity in the range of 5 °C–45 °C and 55 to 600 μS/cm, respectively.

Pb(II) Determination in a Single Drop Using a Modified Screen-Printed Electrode

This work presents the development and validation of an electroanalytical method for Pb(II) determination in a single drop. The electrochemical sensors used were an unmodified screen-printed electrode (SPE) and a Bi-film SPE (BiFSPE). Anodic square wave stripping voltammetry (SWASV) was performed at an accumulation potential of −1.5 V vs. Ag/AgCl and an accumulation time of 60 s. Electroanalysis with an unmodified SPE did not yield satisfactory results, whereas the BiFSPE was a much better analysis method. The linear concentration using the BiFSPE was in the range of 138.8–162.5 µg/L. The accuracy and precision were evaluated for different spiked concentrations, but the method using the unmodified SPE was neither accurate nor precise. Using the BiFSPE, the method was found to be both accurate and precise for Pb(II) determination at a concentration of 140.0 μg/L, with recovery and relative standard deviation (RSD) of 106.6% and 12.1%, respectively. In addition, using the BiFSPE, LOD and LOQ values of 1.2 μg/L and 3.3 μg/L were obtained, respectively. The possible interference effect on Pb(II) stripping signal was checked in the presence of Cd(II), Zn(II), Cu(II), Sn(IV), Sb(III), Hg(II), Fe(III), As(V), K(I), I−, Ca(II), and NO3−. Electrochemical impedance spectroscopy measurements were also performed for the unmodified SPE and BiFSPE. The application of single drop Pb(II) analysis was tested by real water sample analysis.

Kinetic Study of the Cd-Biopolyelectrolyte Complexes Formation Using Square Wave Stripping Voltammetry

In this work an electrochemical methodology was developed to follow the association kinetics between a heavy metals and two different biopolymers, BP (corn gum and chitosan). This type of interaction is a key factor in the removal of metal ions contained in aqueous media at low concentrations. An aqueous solution with ppm of cadmium was used as a model to evaluate the kinetics of formation of the Cd-BP complex. The method selected for the quantification of cadmium was the square wave stripping voltammetry (SWSV). The experiment was carried out using a Britton-Robinson solution as a support electrolyte at pH 4.5, vitreous carbon as a working electrode, Calomel as a reference electrode, and graphite as a counter electrode. The initial concentration of Cd (II) solution was 10 mg/L. The concentration changes were recorded during 590 s. The kinetic models chosen to identify the reaction mechanism of the complex formation process were reversible first order and pseudo first order.

Studies of mechanism, kinetic model and determination of bupivacaine and its application pharmaceutical forms

Bupivacaine, a local anesthetic that is often preferred in many wide ophthalmology applications, was investigated from different aspects such as electrochemical behavior, kinetic model, mechanism illumination, and analytical applications by cyclic voltammetry (CV) and square wave stripping voltammetry (SWSV) methods on glassy carbon electrode (GCE). Bupivacaine exhibited a well-defined anodic signal at nearly 850 mV, an irreversible and adsorption-controlled electrode process. Furthermore, a sensitive and selective SWSV method with a linear working range of 0.3–12.5 mg/L was developed for bupivacaine determination. Limits of detection (LOQ) and that of determination (LOD) were analyzed as 85 and 282 μg/L, respectively. In addition, the most probable study mechanism was carried out for the first time by this study. The selectivity of some co-existences such as heavy metals, ketotifen, moxifloxacin, ciprofloxacin, cyclopentanate and tropicamide was studied in 1 mg/L bupivacaine determination. They did not have a serious effect on bupivacaine determination at 5% tolerance limits. Otherwise, bupivacaine was successfully analyzed in matrix samples without any pretreatment by the proposed SWSV. Consequently, a fast, reliable, inexpensive, portable, eco-friendly, and sensitive new method has been developed to analyze bupivacaine in real samples.

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.

Highly sensitive and selective sensor based on molecularly imprinted polymer for voltammetric determination of Nevirapine in biological samples

Abstract In the present study, a sensitive electrochemical sensor based on the molecularly imprinted polymer (MIP) was designed for measuring of Nevirapine (NVP). The non-imprinted polymer (NIP) and also MIP were synthesized then mixed with other compounds (graphite powder and paraffin oil) for the fabrication of the carbon paste electrodes (CPEs) to NVP analysis. The NIP/CP and MIP/CP electrodes were characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) methods. The constructed sensor was utilized for NVP analysis using an oxidation peak of NVP in the square wave stripping voltammetry (SWSV) method. The calibration curve has consisted of a linear portion in the concentration range of 0.05–300 μM with the limit of detection (LOD) value of 10 nM. The MIP sensor demonstrated reproducible behavior and also, a high level of stability in all electrochemical experiments. Besides, analytical parameters were optimized, and the results were compared with similar results reported in the previous studies. The purposed sensor was successfully used for the quantitative measurement of this drug in the pharmaceutical dosage form and human blood serum samples.

Signal amplification by electro-oligomerisation for improved isoproturon detection

A novel concept is introduced for signal amplification in electrochemical sensing: the electro-oligomerisation stripping voltammetry, which has been applied here to the improved detection of the isoproturon herbicide in spring waters as a proof-of-principle. It involves a potentiostatic accumulation step onto a glassy carbon electrode (at +1.5 V vs Ag/AgCl reference electrode for 300 s) leading to the formation of an oligomeric film, which is then detected by cathodic stripping square wave voltammetry (SWV). The presence and composition of the film are confirmed by confocal Raman spectroscopy. Its characterisation by cyclic voltammetry demonstrates the reversible nature of the electrodeposited material, confirming its interest for sensitive detection by SWV. Adding a mesoporous silica membrane with vertically oriented nanochannels further enhances the sensitivity of the sensor, exhibiting a linear response in the 10–100 μM concentration range. This effect was even more interesting for real media analysis thanks to the permselective properties of such nanoporous coating in rejecting interferences and/or surface fouling agents. The method should be applicable to other analytes that are usually not detectable by conventional accumulation/stripping voltammetry.