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A simple method has been developed for the preconcentration of mercury based on the adsorption of its Schiff's base diphenylthiocarbazone (DPC)complex on a silica gel-immobilized Schiff's base diphenylthiocarbazone (DPC)column.The influence of acidity, eluting agents, stability of the column, sample volume and interfering ions has been investigated in detail. The adsorbed complex could be' eluted using environmentally benign polyethylene glycol (PEG 400) and the concentration of mercury was determined by visible spectrophotometry at a wavelength maximum of 535 nm. A detection limit of 5 ugL ' could be achieved and the developed procedure was successfully applied for the determination of mercury in spiked water samples. The preconcentration factor attainable for quantitative recovery (>96%) of mercury(II) was 100 for a 1000mL sample volume. Source

Moghimi A.,Islamic Azad University at East Tehran | Poursharifi M.J.,Islamic Azad University at Saveh
Asian Journal of Chemistry | Year: 2011

Dispersive liquid-liquid microextraction (DLLME) technique was successfully used as a sample preparation method for graphite furnace atomic absorption spectrometry (GF AAS). In this extraction method, 500 μL methanol (disperser solvent) containing 34 μL carbon tetrachloride (extraction solvent) and 0.00010 g N-benzoyl-N-phenylhydroxylamine was rapidly injected by syringe into the water sample containing cadmium ions. A cloudy solution is formed. The cloudy state resulted from the formation of fine droplets of carbon tetrachloride, which have been dispersed, in bulk aqueous sample. At this stage, cadmium reacts with N-benzoyl-N-phenylhydroxylamine and therefore, hydrophobic complex forms which is extracted into the fine droplets of carbon tetrachloride. After centrifugation (2 min at 5000 rpm), these droplets were sedimented at the bottom of the conical test tube (25 ± 1 μL). Then a 20 μL of sedimented phase containing enriched analyte was determined by GF AAS. Some effective parameters on extraction and complex formation, such as extraction and disperser solvent type and their volume, extraction time, salt effect, pH and concentration of the chelating agent have been optimized. Under the optimum conditions, the enrichment factor 118 was obtained from only 5.00 mL of water sample. The calibration graph was linear in the rage of 2-21 ng L -1 with detection limit of 0.6 ng L -1. The relative standard deviation (RSDs) for ten replicate measurements of 20 ng L -1 of cadmium was 3.1 %. The relative recoveries of cadmium in tap, sea and rain water samples at spiking level of 5 and 10 ng L -1 are 98, 94, 96 and 93 %, respectively. The characteristics of the proposed method have been compared with cloud point extraction, on-line liquidliquid extraction, single drop microextraction, on-line solid phase extraction and co-precipitation based on bibliographic data. Therefore, dispersive liquid-liquid microextraction combined with graphite furnace atomic absorption spectrometry is a very simple, rapid and sensitive method, which requires low volume of sample (5.00 mL). Source

Poursharifi M.J.,Islamic Azad University at Saveh | Moghimi A.,Islamic Azad University at East Tehran
Asian Journal of Chemistry | Year: 2011

A new approach for a cloud point extraction electrothermal atomic absorption spectrometric method was used for determining bismuth. The aqueous analyte was acidified with sulfuric acid (pH 3.0-3.5). Triton X-114 was added as a surfactant and sodium diethyldithiocarbamate was used as a complexing agent. After phase separation at 50 °C based on the cloud point separation of the mixture, the surfactantrich phasewas diluted using tetrahydrofuran. Twenty microliters of the enriched solution and 10 μL of 0.1 % (w/v) Pd(NO 3) 2 as chemical modifier were dispersed into the graphite tube and the analyte determined by electrothermal atomic absorption spectrometry. After optimizing extraction conditions and instrumental parameters, a preconcentration factor of 195 was obtained for a sample of only 10 mL. The detection limit was 0.04 ng mL -1 and the analytical curve was linear for the concentration range of 0.04-0.70 ng mL -1. Relative standard deviations were < 5 %. The method was successfully applied for the extraction and determination of bismuth in samples water. Source

Mostofi M.,Islamic Azad University at East Tehran | Nosrat A.H.,Queens University | Pearce J.M.,Queens University
International Journal of Environmental Science and Technology | Year: 2011

Due to the negative environmental effects of fossil fuel combustion, there is a growing interest in both improved efficiency in energy management and a large-scale transition to renewable energy systems. Using both of these strategies, a large institutional-scale hybrid energy system is proposed here, which incorporates both solar photovoltaic energy conversion to supply renewable energy and cogeneration to improve efficiency. In this case, the photovoltaic reduces the run time for the cogeneration to meet load, particularly in peaking air conditioning times. In turn, however, the cogeneration system is used to provide power back up for the photovoltaic during the night and adverse weather conditions. To illustrate the operational symbiosis between these two technical systems, this study provides a case study of a hybrid photovoltaic and cogeration system for the Taleghani hospital in Tehran. Three design scenarios using only existing technologies for such a hybrid system are considered here:1) single cogeneration + photovoltaic, 2) double cogeneration + photovoltaic, 3) single cogeneration + photovoltaic + storage. Numerical simulations for photovoltaic and cogeneration performance both before and after incorporating improved thermal energy management and high efficiency lighting were considered. The results show that the total amount of natural gas required to provide for the hospitals needs could be lowered from the current status by 55% for scenario 1 and 62% for both scenarios 2 and 3, respectively. This significant improvement in natural gas consumption illustrates the potential of hybridizing solar photovoltaic systems and cogeneration systems on a large scale. © IRSEN, CEERS, IAU. Source

Haghparast M.,Islamic Azad University at East Tehran
Ships and Offshore Structures | Year: 2016

In magnetohydrodynamic (MHD) seawater thrusters, a lot of energy is stored in the superconducting coil which produces the magnetic field. Although it is necessary to store this energy in the field coil to produce a constant thrust, on the way back to the beach and before mooring, this energy can be used to supply the required electricity of the ship equipment. This will lead to consumption of the field coil energy and will reduce the magnetic field intensity in the channel with a decaying exponential function. In this study, an approximate analytical solution is presented to predict the transient behaviour of the MHD thruster with decaying exponential magnetic field. Using this analysis, the maximum navigable distance and the maximum speed of a hypothetical MHD vessel are calculated as a function of Stuart number, electromagnetic interaction number, Reynolds number, and the time constant. The results show that the electromagnetic parameter and the Stuart number can be considered as measures of electromotive and counter-electromotive forces of the MHD thruster, respectively. These two parameters are the most important factors in increasing and decreasing the maximum navigable distance of the MHD vessel. © 2016 Informa UK Limited, trading as Taylor & Francis Group Source

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