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 Cd(2+), Pb(2+) and Hg(2+). 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 Cd(2+), 0.01 mg L(-1) of Pb(2+) and 0.001 mg L(-1) of Hg(2+.), 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 Pb(2+), Cd(2+) and Hg(2+) as analysed using the double reciprocal plots of the Michaelis-Menten equation was found to be reversible and uncompetitive inhibition. Based on the Km(app) 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.
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 (Pt(2+)), palladium (Pd(2+)) or rhodium (Rh(2+)) 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 Pt(2+), Pd(2+) and Rh(2+) 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.
Mercury measurements were concurrently made in air (Gaseous Elemental Mercury, i.e. GEM) as well as in precipitation samples (Total mercury, i.e. TotHg) over a seven year period (2007-2013) at Cape Point, South Africa, during the rainy seasons (May-October). Eighty-five rain events, almost exclusively associated with cold fronts, have been identified of which 75% reached the Cape Point observatory directly across the Atlantic Ocean from the south, while 19% moved in to the measuring site via the Cape Town metropolitan region. In statistic terms the GEM, TotHg, CO and 222Rn levels within the urban-marine events do not differ from those seen in the marine rain episodes. Over the 2007-2013 period, the May till Oct averages for GEM ranged from 0.913 ng m-3 to 1.108 ng m-3, while TotHg concentrations ranged from 0.03 to 52.5 ng L-1 (overall average: 9.91 ng L-1). A positive correlation (R2 = 0.49, n = 7) has been found between the average annual (May till October) GEM concentrations in air and TotHg concentration in rainwater suggesting a close relationship between the two species. The wetter years are normally associated with higher GEM and TotHg levels. Both GEM and TotHg annual means correlate positively with total annual (May till October) rain depths. If one or two outlier years are removed from the data set, the R2 values increase from 0.23 to 0.10 for GEM and TotHg to 0.97 (n = 5) and 0.89 (n = 5), respectively. The relationship between annual mean GEM and annual precipitation depth also holds for the period 1996-2004 (R2 = 0.6, n = 8) when GEM was measured manually (low resolution data). A positive correlation was also seen between annual average GEM concentrations and the El Nifio Southern Oscillation (ENSO) Index (SOI), for the 1996-2004 period (R2 = 0.7, n = 8). For the 2007-2013 periods this relationship was also positive but less pronounced. The relationship between annual precipitation depth and annual SOI suggests that the inter-annual variations of GEM (Hg0) concentration might be caused by large-scale meteorological processes. (C) 2015 Elsevier Ltd. All rights reserved
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