Vernon Somerset

Stripping voltammetric determination of palladium, platinum and rhodium in freshwater and sediment samples from South African water resources

Stripping voltammetry as technique has proved to be very useful in the analysis of heavy and other metal ions due to its excellent detection limits and its sensitivity in the presence of different metal species or interfering ions. Recent assessments of aquatic samples have shown increased levels of platinum group metals (PGMs) in aquatic ecosystems, caused by automobile exhaust emissions and mining activities. The development of an analytical sensor for the detection and characterisation of PGMs were investigated, since there is an ongoing need to find new sensing materials with suitable recognition elements that can respond selectively and reversibly to specific metal ions in environmental samples. The work reported shows the successful application of another mercury-free sensor electrode for the determination of platinum group metals in environmental samples. The work reported in this study entails the use of a glassy carbon electrode modified with a bismuth film for the determination of platinum (Pt2+), palladium (Pd2+) or rhodium (Rh2+) by means of adsorptive cathodic stripping voltammetry. Optimised experimental conditions included composition of the supporting electrolyte, complexing agent concentration, deposition potential, deposition time and instrumental voltammetry parameters for Pt2+, Pd2+ and Rh2+ determination. Adsorptive differential pulse stripping voltammetric measurements for PGMs were performed in the presence of dimethylglyoxime (DMG) as complexing agent. The glassy carbon bismuth film electrode (GC/BiFE) employed in this study exhibit good and reproducible sensor characteristics. Application of GC/BiFE sensor exhibited well-defined peaks and highly linear behaviour for the stripping analysis of the PGMs in the concentration range between 0 and 3.5 μg/L. The detection limit of Pd, Pt and Rh was found to be 0.12 μg/L, 0.04 μg/L and 0.23 μg/L, respectively for the deposition times of 90 s (Pd) and 150 s (for both Pt and Rh). Good reproducibility was also observed and the practical applicability of the sensor was demonstrated with the analysis of environmental water and sediment samples.

Amperometric determination of cadmium, lead, and mercury metal ions using a novel polymer immobilised horseradish peroxidase biosensor system

This work was undertaken to develop a novel Pt/PANI-co-PDTDA/HRP biosensor system for environmental applications to investigate the inhibition studies by specific heavy metals, to provide data suitable for kinetic studies and further application of the biosensor to environmental samples. The newly constructed biosensor was compared to the data of the well-researched Pt/PANI/HRP biosensor. Optimised experimental conditions, such as the working pH for the biosensor was evaluated. The functionality of the amperometric enzyme sensor system was demonstrated by measuring the oxidation current of hydrogen peroxide followed by the development of an assay for determination of metal concentration in the presence of selected metal ions of Cd2+, Pb2+ and Hg2+. The detection limits were found to be 8 × 10−4 μg L−1 for cadmium, 9.38 × 10−4 μg L−1 for lead and 7.89 × 10−4 μg L−1 for mercury. The World Health Organisation recommended that the maximum safety level of these metals should not exceed 0.005 mg L−1 of Cd2+, 0.01 mg L−1 of Pb2+ and 0.001 mg L−1 of Hg2+., respectively. The analytical and detection data for the metals investigated were observed to be lower than concentrations recommended by several bodies including World Health Organisation and Environmental Protection Agencies. Therefore the biosensors developed in this study can be used to screen the presence of these metals in water samples because of its low detection limit. The modes of inhibition of horseradish peroxidase by Pb2+, Cd2+ and Hg2+ as analysed using the double reciprocal plots of the Michaelis–Menten equation was found to be reversible and uncompetitive inhibition. Based on the Kmapp and Imax values for both biosensors the results have shown smaller values. These results also proved that the enzyme modified electrode is valuable and can be deployed for the determination or screening of heavy metals.

Synthesis and Characterization of Bismuth-Silver Nanoparticles for Electrochemical Sensor Applications

Silver, bismuth, and bismuth-silver nanoparticles were synthesized and characterized by cyclic voltammetry, electrochemical impedance spectroscopy, ultraviolet-visible spectroscopy, infrared spectroscopy, Raman spectroscopy, and transmission electron microscopy to determine the electrochemical, optical, structural, and morphological properties of the nanomaterials. The silver, bismuth, and bismuth-silver nanoparticles were shown to have an average particle size of 10–30 nanometers by microscopy. The electrochemical results showed that the bismuth-silver nanoparticles exhibited good electrocatalytic activity that can be harnessed for sensor construction and related applications. The ultraviolet-visible, infrared, and Raman spectroscopy results confirmed the structural properties of the bismuth-silver nanoparticles. In addition, the microscopy and electron diffraction morphological characterization confirmed the nature of the bismuth-silver nanoparticles.

Stripping voltammetric measurement of trace metal ions using screen-printed carbon and modified carbon paste electrodes on river water from the Eerste-Kuils River System.

Screen-printed carbon electrodes (SPCEs) and carbon paste electrodes (CPEs) were prepared as “mercury-free” electrochemical sensors for the determination of trace metal ions in aqueous solutions. SPCEs were coated with conducting polymer layers of either polyaniline (PANI), or polyaniline-poly(2,2′-dithiodianiline) (PANI-PDTDA). Furthermore, CPEs containing electroactive compounds with reactivity towards metal ions were employed to obtain enhanced selectivity. Optimised experimental conditions for Hg2+, Pb2+, Ni2+ and Cd2+ determination included the supporting electrolyte concentration, deposition potential (E d) and accumulation time (t acc). For the modified carbon paste sensors (MCPEs) it was found that −400 mV is an adequate deposition potential and an accumulation time of 120 s was adequate for the determination using the different constructed electrodes. Initial results showed linearity in the examined concentration range between 1 × 10−9 M and 1 × 10−6 M using the SPCE/PANI-PDTDA sensor on laboratory prepared standard solutions, while good selectivity for the different metal ions were obtained. Furthermore, the limit of detection (LOD) was determined for each of the sensors and for the SPCE/PANI-PDTDA sensor it was found to be 2.2 × 10−13 M, while for the SPCE/PANI sensor the LOD was determined to be 8.4 × 10−11 M. The MCPE sensors also showed good linearity between the concentration range of 1 × 10−3 to 1 × 10−9 M. The LOD values for the various MCPE sensors, were found to be Hg(II) - 1.3 × 10−7 M; Cd(II) – 2.9 × 10−7 M; Ni(II) – 3.2 × 10−7 M; and Pb(II) – 1.7 × 10−7 M for the CPE/PANI-PDTDA sensor. For the CPE/PANI sensor the LOD values were Hg(II) – 1.5 × 10−5 M; Cd(II) – 8.6 × 10−7 M; Ni(II) – 9.5 × 10−7 M; and Pb(II) – 1.3 × 10−6 M. For the CPE/MBT sensor the LOD values were Hg(II) – 3.8 × 10−5 M; Cd(II) – 1.4 × 10−6 M; Ni(II) – 1 × 10−6 M; and Pb(II) – 6.3 × 10−5 M. Very low detection was obtained for the SPCE/PANI-PDTDA sensor in Hg2+ determination, while the MCPE sensors delivered sensitive simultaneous detection for Hg2+, Pb2+, Ni2+ and Cd2+ metal ions.

Inhibitive Determination of Metal Ions Using a Horseradish Peroxidase Amperometric Biosensor

The development of electro-analytical methods for the determination of mercury, lead, cadmium and various other trace metals in acidic media or at different pH values are not new and for that reason, the investigation of alternative techniques have been ongoing and especially to find mercury-free electrodes (Ugo et al., 1995). Stripping voltammetry has been widely used for trace metal analysis with mercury as the working electrode due to its remarkable analytical properties. However, due to the toxicity of mercury and the human health risk that it poses (bioaccumulation in the food chain), there have been in‐ sistent efforts to remove the use of mercury completely. Electroanalysis has therefore seen the use of mercury-free sensors, while much attention has been dedicated to the develop‐ ment of such sensors over the last decade (Hwang et al., 2008; Sonthalia et al., 2004). Sev‐ eral heavy metals create environmental and human health concerns when elevated concentrations of these metals are present in the environment. In this regard, lead (Pb) and mercury (Hg) and more increasingly cadmium (Cd) heavy metals are of prime envi‐ ronmental concern, since they are significant for environmental surveillance, food control, occupational medicine, toxicology and hygiene (Ensafi and Zarei, 2000). Lead (Pb) is fur‐ thermore constantly monitored in natural and drinking water due to the harmful effects that are often manifested in young children (Zen et al., 2002). It is also known that several trace metals are regarded as essential micro-nutrients and play an integral role in the life processes of living organisms. In contrast, metals such as aluminium, silver, cadmium, gold, lead and mercury play no biological role in living organisms and lead to toxicity

Solanum melongena polyphenol oxidase biosensor for the electrochemical analysis of paracetamol.

ABSTRACT A new strategy for the construction of a polyphenol oxidase carbon paste biosensor for paracetamol detection is reported. The eggplant (Solanum melongena) was processed to collect the polyphenol oxidase as an enzyme that was incorporated in the carbon paste sensor construction. The constructed sensor displayed high sensitivity and good selection for paracetamol detection and recognition. Optimized conditions included pH 6.0 (highest activity), pH 7.0 (highest stability), pulse amplitude of 50 mV, and 15% of vegetable extract per carbon paste. The sensor displayed a linear range from 20 to 200 µM, with a detection limit of 5 µM. Application of the sensor to paracetamol determination in tablet and oral solutions have shown satisfactory results. The efficiency of the method showed very good repeatability ranging between 1.26 and 1.72% relative standard deviation for interday analysis, while recoveries for paracetamol varied between 97.5 and 99.8% for the voltammetric determination. The strategy for a simple, low cost, and efficient eggplant polyphenol oxidase sensor showcased in this work provides an opportunity for the detection of other phenolic compounds in various matrices.

The Use of a Polyphenoloxidase Biosensor Obtained from the Fruit of Jurubeba (Solanum paniculatum L.) in the Determination of Paracetamol and Other Phenolic Drugs

The vegetable kingdom is a wide source of a diverse variety of enzymes with broad biotechnological applications. Among the main classes of plant enzymes, the polyphenol oxidases, which convert phenolic compounds to the related quinones, have been successfully used for biosensor development. The oxidation products from such enzymes can be electrochemically reduced, and the sensing is easily achieved by amperometric transducers. In this work, the polyphenoloxidases were extracted from jurubeba (Solanum paniculatum L.) fruits, and the extract was used to construct a carbon paste-based biosensor for pharmaceutical analysis and applications. The assay optimization was performed using a 0.1 mM catechol probe, taking into account the amount of enzymatic extract (50 or 200 μL) and the optimum pH (3.0 to 9.0) as well as some electrochemical differential pulse voltammetric (DPV) parameters (e.g., pulse amplitude, pulse range, pulse width, scan rate). Under optimized conditions, the biosensor was evaluated for the quantitative determination of acetaminophen, acetylsalicylic acid, methyldopa, and ascorbic acid. The best performance was obtained for acetaminophen, which responded linearly in the range between 5 and 245 μM (R = 0.9994), presenting a limit of detection of 3 μM and suitable repeatability ranging between 1.52% and 1.74% relative standard deviation (RSD).

Application of a Bismuth-Silver Nanosensor for the Simultaneous Determination of Pt-Rh and Pd-Rh Complexes

The present work describes the development of an electrochemical sensor for the simultaneous determination of Pd-Rh and Pt-Rh complexes using a bismuth-silver bimetallic nanofilm modified glassy carbon electrode. The electrochemical sensor was prepared by drop-casting bismuth-silver bimetallic nanoparticles on to glassy carbon electrode surfaces. The HRTEM microscopy and UV-Vis spectroscopy results of the bismuth-silver nanoparticles were compared with other work in literature. The developed nanosensor exhibited a linear working range of 0.4 - 1.4 ng/L for Pd-Rh and 0.8-1.2 ng/L for Pt-Rh DMG complexes, respectively. Very low detection limits (S/N = 3) of 0.19 ng/L for Pd (II), 0.2 ng/L Pt (II) and 0.22 ng/L for Rh (III) were obtained and the sensor was successfully applied to environmental samples.

A brief review on recent developments of electrochemical sensors in environmental application for PGMs

ABSTRACT This study offers a brief review of the latest developments and applications of electrochemical sensors for the detection of Platinum Group Metals (PGMs) using electrochemical sensors. In particular, significant advances in electrochemical sensors made over the past decade and sensing methodologies associated with the introduction of nanostructures are highlighted. Amongst a variety of detection methods that have been developed for PGMs, nanoparticles offer the unrivaled merits of high sensitivity. Rapid detection of PGMs is a key step to promote improvement of the public health and individual quality of life. Conventional methods to detect PGMs rely on time-consuming and labor intensive procedures such as extraction, isolation, enrichment, counting, etc., prior to measurement. This results in laborious sample preparation and testing over several days. This study reviewed the state-of-the-art application of nanoparticles (NPs) in electrochemical analysis of environmental pollutants. This review is intended to provide environmental scientists and engineers an overview of current rapid detection methods, a close look at the nanoparticles based electrodes and identification of knowledge gaps and future research needs. We summarize electrodes that have been used in the past for detection of PGMs. We describe several examples of applications in environmental electrochemical sensors and performance in terms of sensitivity and selectivity for all the sensors utilized for PGMs detection. NPs have promising potential to increase competitiveness of electrochemical sensors in environmental monitoring, though this review has focused mainly on sensors used in the past decade for PGMs detection. This review therefore provides a synthesis of outstanding performances in recent advances in the nanosensor application for PGMs determination.

Nanostructured TiO2 Carbon Paste Based Sensor for Determination of Methyldopa

Methyldopa is a catecholamine widely used in the treatment of mild to moderate hypertension whose determination in pharmaceutical formulae is of upmost importance for dose precision. Henceforth, a low-cost carbon paste electrode (CPE) consisting of graphite powder obtained from a crushed pencil stick was herein modified with nanostructured TiO2 (TiO2@CPE) aiming for the detection of methyldopa in pharmaceutical samples. The TiO2-modified graphite powder was characterized by scanning electron microscopy and X-ray diffraction, which demonstrated the oxide nanostructured morphology. Results evidenced that sensitivity was nonetheless increased due to electro-catalytic effects promoted by metal modification, and linear response obtained by differential pulse voltammetry for the determination of methyldopa (pH = 5.0) was between 10–180 μmol/L (Limit of Detection = 1 μmol/L) with the TiO2@CPE sensor. Furthermore, the constructed sensor was successfully applied in the detection of methyldopa in pharmaceutical formulations and excipients promoted no interference, that indicates that the sensor herein developed is a cheap, reliable, and useful strategy to detect methyldopa in pharmaceutical samples, and may also be applicable in determinations of similar compounds.