Renewable Copper and Silver Amalgam Film Electrodes of Prolonged Application for the Determination of Elemental Sulfur Using Stripping Voltammetry

Recent advancements in non-enzymatic electrochemical sensor development for the detection of organophosphorus pesticides in food and environment

Organophosphorus Pesticides (OPPs) are among the extensively used pesticides throughout the world to boost agricultural production. However, persistent residues of these toxic pesticides in various vegetables, fruits, and drinking water poses detrimental health effects. Consequently, the rapid monitoring of these harmful chemicals through simple and cost-effective methods has become crucial. In such an instance, electrochemical methods offer simple, rapid, sensitive, reproducible, and affordable detection pathways. To overcome the limitations associated with electrochemical enzymatic sensors, non-enzymatic sensors have emerged as promising and simpler alternatives. The non-enzymatic sensors have demonstrated superior activity, reaching detection limit up to femto (10-15) molar concentration in recent years, leveraging higher selectivity obtained through the molecularly imprinted polymers, synergistic effects between carbonaceous nanomaterials and metals, metal oxide alloys, and other alternative approaches. Herein, this review paper provides an overview of the recent advancements in the development of non-enzymatic electrochemical sensors for the detection of commonly used OPPs, such as Chlorpyrifos (CHL), Diazinon (DZN), Malathion (MTN), Methyl parathion (MP) and Fenthion (FEN). The design method of the electrodes, electrode functioning mechanism, and their analytical performance metrics, such as limit of detection, sensitivity, selectivity, and linearity range, were reviewed and compared. Furthermore, the existing challenges within this rapidly growing field were discussed along with their potential solutions which will facilitate the fabrication of advanced and sustainable non-enzymatic sensors in the future.

Assessment of the performance of triphenylphosphine for the voltammetric determination of elemental sulphur in cosmetic products

In this paper, an alternative voltammetric method for the determination of elemental sulphur in cosmetic products is presented. It is based on the decrease of triphenylphosphine oxidation current in the presence of elemental sulphur by using a glassy carbon electrode. A solution of 2% (m/v) acetic acid and 0.6 mol L-1 sodium acetate in methanol was used as a supporting electrolyte. The experimental conditions for indirect determination of elemental sulphur were established. Using square-wave voltammetry, the analytical curve was linear in the elemental sulphur concentration range of 9.94-271 μmol L-1, with a detection limit of 2.59 μmol L-1. The method was successfully applied to determine elemental sulphur in soap bars and anti-acne cream, without any preliminary sample treatment, therefore, it is shortened and simplified. The results obtained with the indirect voltammetric method were not statistically different in comparison with a titrimetric one, at a 95% confidence level. Additionally, excellent recovery percentages were obtained, proving no matrix interferences.

Electrochemical determination of closantel in the commercial formulation by square-wave adsorptive stripping voltammetry

ABSTRACT

In this paper, the square-wave adsorptive stripping voltammetric (SWAdSV) determination of the veterinary drug closantel using a renewable silver amalgam film electrode (Hg(Ag)FE) is presented. As observed in SWAdSV, closantel provided one well-shaped reduction peak suitable for analytical purposes at potential ca. -1.4 V in the Britton-Robinson (B-R) buffer at pH 7.0. At optimal conditions, the SWAdSV response of Hg(Ag)FE for determining closantel was linear over two concentration ranges of 5.0 × 10-8 to 2.0 × 10-7 mol dm-3 and 2.0 × 10-7 to 1.2 × 10-6 mol dm-3 with a detection limit of 1.1 × 10-8 mol dm-3. In addition, a relevance of the developed SWAdSV method was successfully verified by the quantitative analysis of closantel in the commercial formulation Closamectin Pour-On with satisfactory results (RSD = 5.8%, recovery = 101.8%). The results showed that the developed procedure can be adequate for screening purposes. Also, the electrochemical behavior of closantel was characterized by cyclic voltammetry, and it was found that closantel exhibited a quasi-reversible behavior with cathodic peak on the forward scan at ca. -1.4 V and anodic peak on the reverse scan at ca. -1.35 V vs. Ag/AgCl in B-R buffer, pH 7.0. As the obtained results showed that the electrode mechanism of closantel is controlled by the adsorption, the effect of adsorption was studied using the electrochemical impedance spectroscopy technique.

GRAPHICAL ABSTRACT

Electrode mechanism and voltammetric determination of selected guanidino compounds

The present review describes the recent results on the electrochemical activity of bio-guanidino compounds, such as famotidine, metformin, acyclovir, ganciclovir, zanamivir, moroxydine as well as guanidino compounds, such as S-[(2-guanidino-thiazol-4-yl)methyl]isothiourea hydrochloride, 2-guanidino-1,3-thiazole, 2-guanidinobenzimidazole. The focus is on analyzing the electrode mechanism of the guanidino compounds at the hanging mercury drop electrode and at the silver amalgam film electrode, as well as on the character of the square wave (SW) voltammetric signals. It has been stated, that the compounds can act as electrocatalysts — they are protonated and adsorbed at the surface of the electrode, after which the protonated forms of the compounds are irreversibly reduced, yielding their initial form and hydrogen. The experimental adsorption data obtained by measuring the differential capacity of the double layer, the zero charge potential, and the surface tension at the zero charge potential have established the adsorption processes underlying their electrochemical activity. The analytical application of the obtained voltammetric signals in the determination of these compounds in biological samples is also presented. This review concentrates on our own results in the context of general developments in the field.

Screen-printed carbon electrodes modified with cobalt phthalocyanine for selective sulfur detection in cosmetic products

Cobalt phthalocyanine (CoPc) films were deposited on the surface of a screen-printed carbon electrode using a simple drop coating method. The cyclic voltammogram of the resulting CoPc modified screen-printed electrode (CoPc/SPE) prepared under optimum conditions shows a well-behaved redox couple due to the (Co(I)/Co(II)) system. The CoPc/SPE surface demonstrates excellent electrochemical activity towards the oxidation of sulfur in a 0.01 mol·L(-1) NaOH. A linear calibration curve with the detection limit (D(L), S/N = 3) of 0.325 mg·L(-1) was achieved by CoPc/SPE coupled with flow injection analysis of the sulfur concentration ranging from 4 to 1120 mg·L(-1). The precision of the system response was evaluated (3.60% and 3.52% RSD for 12 repeated injections), in the range of 64 and 480 mg·L(-1) sulfur. The applicability of the method was successfully demonstrated in a real sample analysis of sulfur in anti-acne creams, and good recovery was obtained. The CoPc/SPE displayed several advantages in sulfur determination including easy fabrication, high stability, and low cost.