Square-wave Adsorptive Stripping Voltammetry Method Research Articles

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.

Adsorption and determination of sibutramine in illegal slimming product using porous graphene ink-modified electrode

This work presents a new material, i.e., a porous graphene ink to modify on the GCE surface (PGr-ink/GCE) to improve sensitivity by increasing the surface area of the electrode for the electrochemical determination of sibutramine. The surface characterization and electrochemical adsorption behavior of the PGr-ink/GCE toward sibutramine were investigated using scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), ATR-FTIR spectroscopy and square wave adsorptive stripping voltammetry (SWAdSV). The PGr-ink/GCE exhibited a distinctive anodic response towards sibutramine using SWAdSV in BR buffer (pH 8.00) with a sensitivity 4 times higher than the bare GCE. Under the optimum conditions, the modified electrode showed good electrochemical adsorption and detection of sibutramine by the SWAdSV method with two ranges of linear concentration from 0.015 to 10.0 μg mL−1 and 10–50 μg mL−1. The limit of detection and quantitation were 5 ng mL−1 and 15 ng mL−1, respectively. Over a short analysis time (180 s), the sensor exhibited high sensitivity (10.9 μAμg−1mLcm−2), good reproducibility (RSD <3.4% n = 6), repeatability (RSD between 1.8 and 9.8% (n = 15)), excellent anti-interference properties and was successfully applied for the quantification of sibutramine in different brands of illegal slimming products with good recoveries (93 ± 4–104 ± 1%). The developed electrochemical sibutramine sensor is suitable for application in detecting illegal components in slimming products.

Sensitive and Selective Pathway of Total Antioxidant Capacity in Commercially Lemon, Watermelon and Mango-pineapple Cold Teas by Square Wave Adsorptive Stripping Voltammetry

The present work describes a convenient method for the sensitive and selective pathway of total antioxidant capacity (TAC) in lemon, watermelon and mango-pineapple cold teas by square wave adsorptive stripping voltammetry (SWAdSV) that is major electroanalytical methods on a carbon paste electrode. Anodic peak current of p-coumaric acid exhibited a well oxidation peak at 780 mV was used as a standard to evaluate TAC in tea samples. In addition, the very well-resolved and reproducible anodic processes, such as accumulation time, frequency, step potential etc. were optimized for the SWAdSV method. The potential applicability of the proposed SWAdSV was illustrated in commercial teas samples. SWAdSV proved to be a faster and easier method to calculate TAC compared to other conventional methods. Furthermore, total antioxidant amounts of commercially lemon, watermelon and mango-pineapple cold teas were found in optimum condition as equivalent to a concentration of 2050±15mg/L, 705±10 mg/L and 808±14 mg/L p-coumaric acid (n=3, 95% confidence level), respectively.

Determination of tryptamine in foods using square wave adsorptive stripping voltammetry

Tryptamine, a biogenic amine, is an indole derivative with an electrophilic substituent at the C3 position of the pyrrole ring of the indole moiety. The electrochemical oxidation of tryptamine was investigated using glassy carbon electrode (GCE), and focusing on trace level determination in food products by square wave adsorptive stripping voltammetry (SWAdSV). The electrochemical responses of tryptamine were evaluated using differing voltammetric techniques over a wide pH range, a quasi-reversible electron-transfer to redox system represented by coupled peaks P1–P3, and an irreversible reaction for peak P2 were demonstrated. The proton and electron counts associated with the oxidation reactions were estimated. The nature of the mass transfer process was predominantly diffusion-limited for the oxidation process of P1, the most selective and sensitive analytical response (acetate buffer solution pH 5.3), being used for the development of SWAdSV method, under optimum conditions. The excellent response allowed the development of an electroanalytical method with a linear response range of from 4.7–54.5)×10−8molL−1, low detection limit (0.8×10−9molL−1), and quantification limit (2.7×10–9molL−1), and acceptable levels of repeatability (3.6%), and reproducibility (3.8%). Tryptamine content was determined in bananas, tomatoes, cheese (mozzarella and gorgonzola), and cold meats (chicken sausage and pepperoni sausage), yielding recoveries above 90%, with excellent analytical performance using simple and low cost instrumentation.

Electrochemical determination of rosiglitazone by square-wave adsorptive stripping voltammetry method

Square-wave adsorptive stripping voltammetry technique was used to determine rosiglitazone (ROS) on the hanging mercury dropping electrode (HMDE) surface, in Britton Robinson buffer, pH=5. The voltammetric cathodic peak was observed at −1520mV vs. Ag/AgCl reference electrode. The voltammetric peak response was characterized with respect to pH, supporting electrolyte, accumulation potential, preconcentration time, scan rate, frequency, pulse amplitude, surface area of the working electrode and the convection rate. Under optimal conditions, the voltammetric current is proportional to the concentration of ROS over the concentration range of 5×10−8–8×10−7moll−1 (r=0.9899) with a detection limit of 3.2×10−11moll−1 using 120s accumulation time. The developed SW-AdSV procedure showed a good reproducibility, the relative standard deviation RSD% (n=10) at a concentration level of 5×10−7moll−1 was 0.33%, whereas the accuracy was 101%±1.0. The proposed method was successfully applied to assay the drug in the human urine and plasma samples with mean recoveries of 90±0.71% and 86±1.0%, respectively.

Novel Application of Square-Wave Adsorptive-Stripping Voltammetry for the Determination of Xanthohumol in Spent Hops

This paper reports the development of a novel electrochemical assay for xanthohumol (XN) by square-wave adsorptive-stripping voltammetry (SWAdSV) with a hanging mercury drop electrode. The method showed good repeatability (CV < 2%) and linearity (between 10 and 250 μg L(-1)), as well as suitable limits of detection (2.6 μg L(-1)) and quantification (8.8 μg L(-1)). The method was applied for the quantification of this compound in spent hops, and the results obtained were compared with the HPLC-UV method. XN contents determined by the SWAdSV method were 16 ± 1 and 100 ± 4 μg L(-1) for aqueous and methanolic extracts, respectively. The developed new methodology considerably reduces the analysis time, approximately from 25 min (HPLC-UV method) to 7 min, enabling a high sample throughput. In addition, the detection and quantification limits were approximately 5-fold lower than those obtained with the chromatographic method.

Square‐Wave Adsorptive‐Stripping Voltammetric Detection in the Quality Control of Fluoxetine

Electroanalytical methods based on square‐wave adsorptive‐stripping voltammetry (SWAdSV) and flow‐injection analysis with square‐wave adsorptive‐stripping voltammetric detection (FIA‐SWAdSV) were developed for the determination of fluoxetine (FXT). The methods were based on the reduction of FXT at a mercury drop electrode at −1.2 V versus Ag/AgCl, in a phosphate buffer of pH 12.0, and on the possibility of accumulating the compound at the electrode surface. The SWAdSV method was successfully applied in the quantification of FXT in pharmaceutical products, human serum samples, and in drug dissolution studies. Because the presence of dissolved oxygen did not interfere significantly with the analysis, it was possible to quantify FXT in several pharmaceutical products using FIA‐SWAdSV. This method enables analysis of up to 120 samples per hour at reduced costs.

Electrochemical Determination of Citalopram by Adsorptive Stripping Voltammetry–Determination in Pharmaceutical Products

The electrochemical behavior of citalopram was studied by square‐wave and square‐wave adsorptive‐stripping voltammetry (SWAdSV). Citalopram can be reduced and accumulated at a mercury drop electrode, with a maximum peak current intensity being obtained at a potential of approximately −1.25 V vs. AgCl/Ag, in an aqueous electrolyte solution of pH 12. A SWAdSV method has been developed for the determination of citalopram in pharmaceutical preparations. The method shows a linear range between 1.0×10−7 and 2.0×10−6 mol L−1 with a limit of detection of 5×10−8 mol L−1 for an accumulation time of 30 s. The precision of the method was evaluated by assessing the repeatability and intermediate precision, achieving good relative standard deviations in all cases (≤2.3%). The proposed method was applied to the determination of citalopram in five pharmaceutical products and the results obtained are in good agreement with the labeled values.