QUANTIFICATION OF TOTAL CHROMIUM AND HEXAVALENT CHROMIUM IN WATER BY ELECTROTHERMAL ATOMIC ABSORPTION SPECTROMETRY

The two primary oxidation states of chromium in natural waters, Cr(Ill) and Cr(VI), differsignificantly in biological, geochemical and toxicological properties. Whereas Cr(Ill) isconsidered essential for human in glucose, lipid and protein metabolism, Cr(VI) is toxicbecause of its ability to oxidize other species and its adverse effects on the lung, liver andkidney. Because of the different toxicities and bioavailability of Cr(Ill) and Cr(VI),determination of the total chromium content does not give full information about possiblehealth hazard. Hence monitoring of the concentration of the separate chromium species isof great importance. Many different techniques have been in use for Cr containing samplespreparation and metal ions speciation: ion chromatography, flow injection analysis, andatomic absorption spectrometry (AAS).Procedures for the quantification of total chromium and hexavalent chromium in watersamples arc presented. For the quantification of total chromium and hexavalent chromiumin water Chrornabond NH2 columns (arninopropyl phase with a 3ml volume and 500mg ofsorbent) obtained from Machery- Nagel (Duren, Germany) were used.The pH value of the water sample was adjusted to 5.5 using acetic acid or sodium acetateand sample was aspirated through the previously conditioned column. The column contentswere dried under vacuum and the hexavalent chromium selectively linked was eluted withnitric acid and quantification was performed by Electrothermal Atomic AbsorptionSpectrometry (ET AAS). For the detection of total chromium, Cr(Ill) was transformed intoCr(VI) by oxidizing the sample with 1% K2S20S solution and AgNOJ at 100°C for 15 min.Oxidized solution was eluted through a Chromabond column and total Cr level wasquantified by ET AAS using the same instrumental conditions as for hexavalent chromium.Total chromium was also quantified directly in the water samples using ET AAS. Thetemperature programme of the graphite furnace, the use of chemical modifiers, the atomictechnique employed and the effectiveness of deuterium background correction wereinvestigated. Chromium was reliably determined by without chemical modifiers orbackground correction.The detection limits were 0.4 and 0.5~gll for total chromium and hexavalent chromiumrespectively. The linearity changed under the optimized conditions was 0.4 - 50j.lgll and0.5-50j.lgll and the relative standard deviation was less than 3.5%. The validation of bothprocedures was performed by the standard addition method and the recoveries were higherthan 96% in all cases. It is proved that the method can be successfully employed as analternative to the commonly used preconcentration and speciation analytical techniques.The direct procedure was adopted for the estimation of total chromium in water samples becauseboth procedures applied for total chromium gave similar results. The methods were applied to thedetermination of total chromium and hexavalent chromium in 40 water samples.

An investigation into the effect of rate of stirring of bath electrolyte on the properties of electrodeposited CdTe thin film semiconductors

Electrodeposition (ED) has been recognized as a low cost and scalable technique available for fabrication of CdS/CdTe solar cells. Photovoltaic activity of these electrodeposited semiconductor materials drastically depends on the ED growth parameters namely; electrodeposition potential, concentrations and ratios of concentrations of precursors used to prepare the bath electrolyte, pH of the electrolyte, deposition temperature and rate of stirring of the electrolyte. In order to grow thin films with good photovoltaic properties, it is essential to maintain these variables at their optimum ranges of values during electrodepositions. Hence, this study was conducted to investigate the dependence of the properties of electrodeposited CdTe thin film material on the rate of stirring of the bath electrolyte. The CdTe material was grown on glass/FTO (23 cm2) and glass/FTO/CdS (23 cm2) surfaces in bath electrolytes containing 1.0 mol/L CdSO4 and 1.0 mmol/L TeO2 solutions at different rates of stirring within the range of 0-350 rpm while keeping the values of pH of the electrolyte, deposition temperature and cathodic deposition potential with respect to the saturated calomel electrode at 2.3, 65 °C and 650 mV respectively. After the heat treatment at 400 °C in air atmosphere, the deposited samples with a good visual appearance were selected and evaluated based on their morphological, elemental, structural, optical and electrical properties in order to identify the optimum range of rate of stirring for electrodeposition of CdTe thin film semiconductors. Results revealed that, rates of stirring in the range of 60-85 rpm in a 100 mL volume of electrolyte containing the substrate and the counter electrodes in the center of the bath with a separation of 2.0 cm between them can electrodeposit CdTe layers exhibiting required levels of morphological, structural, optical and electrical properties on both glass/FTO and glass/FTO/CdS surfaces

Toxicity of chlorpyrifos, carbofuran, mancozeb and their formulations to the tropical earthworm Perionyx excavatus.

Effects of chlorpyrifos, carbofuran, mancozeb and their formulated products on survival, growth and reproduction of the tropical earthworm Perionyx excavatus were investigated in standard artificial soil. The toxicity of the three chemicals decreased in the order carbofuran > chlorpyrifos > mancozeb. In general, formulations were more toxic than the active ingredients, but differences in L

Influence of temperature and soil types on the toxicity of three pesticides to Eisenia andrei.

Expansion of agriculture in the tropics has increased the use of pesticides that may affect the soil ecosystems. Few studies so far determined the effects of pesticides in the tropics and tropical risk assessment therefore often relies on data from temperate conditions. Hence we compared the toxicity of chlorpyrifos, carbofuran and carbendazim to the earthworm Eisenia andrei at two different temperatures reflecting temperate and tropical conditions. The toxicity of the three pesticides in both conditions decreased in the order carbendazim > carbofuran > chlorpyrifos. For chlorpyrifos and carbofuran, but not for carbendazim, survival was more sensitive at the higher temperature, probably due to increased earthworm activity. Sub-lethal effects (reproduction and growth) however, varied inconsistently with temperature and soil types. We conclude that toxicity of pesticides in tropics may not be predicted from data generated under temperate conditions, even within the same species. Crown Copyright © 2009

Chlorpyrifos causes decreased organic matter decomposition by suppressing earthworm and termite communities in tropical soil.

Effects of pesticides on structural and functional properties of ecosystems are rarely studied under tropical conditions. In this study litterbag and earthworm field tests were performed simultaneously at the same tropical field site sprayed with chlorpyrifos (CPF). The recommended dose of CPF (0.6 kg a.i. h

Electrodeposition and characterization of as-deposited and annealed CdTe thin films

Thin films of CdTe semiconductor materials were grown on fluorine doped tin oxide (FTO) conducting glass substrates using the technique of electrodeposition. CdSO4 at high concentrations and CdCl2, TeO2 at low concentrations were used as precursor salts for electrodeposition. The range of deposition potentials was estimated using cyclic voltammetric measurements. The electrical, optical, structural and morphological characteristics of as-deposited and annealed CdTe thin films were characterized using photo-electrochemical (PEC) cell studies, UV-Vis spectrophotometry, X-ray diffraction (XRD) and scanning electron microscopy (SEM). These particular samples were converted from n-type into p-type after heat treatment. UV-Vis spectrometric measurements for CdTe layers indicated that, the energy band gaps of 1.45±0.02 eV for both as-deposited and annealed samples which exhibited the required optical property for fabricating CdS/CdTe solar cells. Little increase in (220) and (311) peaks of XRD spectra were observed for annealed layers compared to the as-deposited material. However, annealing exhibited a small reduction of cubic phase preferential orientation (111). The optical transmission for both as-deposited and annealed CdTe samples were about 60% for wavelengths longer than about 850 nm