Annali di chimica最新文献

Sequential chemical extraction was used to assess trace metal speciation and availability in sediments from Abalagada-Aboh catchments in the Niger Delta that have received significant impact of crude oil spillage. The proportions of trace metals in the various geochemical fractions were variable. The result of speciation among the five geochemical fractions indicates that Cd was associated with easily exchangeable/adsorbed and carbonate fractions, Cu and Cr predominantly to organic and residual fraction, Pb was associated with Fe-Mn oxides and carbonate fractions, Ni to residual and Fe-Mn oxides, Mn was associated with Fe-Mn oxides and residual and Zn was associated with carbonate and Fe-Mn oxide fractions. The data revealed that Cd, Pb, Zn and Ni have high mobility indices and are thus relatively labile and bioavailable to aquatic flora and fauna.

A highly sensitive and selective kinetic spectrophotometric method is proposed for the determination of silver in nanogram quantities. The method is based on catalytic activity of silver(I) in enhancing the green colour formation between potassium ferrocyanide and 2,4,6-tripyridyl-1,3,5-triazine (TPTZ) which is otherwise a very slow reaction at pH 2.0. The absorbance spectrum of the green coloured solution in presence of silver showed two peaks of almost equal intensity one at 405 nm and another at 600 nm. At both the wavelengths the absorbance of the experimental solution increased proportionally with the amount of silver(I) in the range 5 – 410 ng mL^-1 and 10 – 610 ng mL^-1 respectively. Other experimental conditions like pH, reagent concentration, ferrocyanide concentration and effect of time for obtaining maximum reaction rate were optimized. The molar absorptivity, Sandell's sensitivity, detection limit, determination limit and relative standard deviation (n = 8) were determined as 1.57 × 106 L mol^-1 cm^-1, 0.065 ng cm^-2, 1.6 ng mL^-1, 4.8 ng mL^-1 and 0.81 % respectively. The effect of various diverse ions on the determination of silver was studied. The method was applied for the determination of silver in alloys, biological samples, effluents, real water and in ayurvedic medicines.

In this study, removal of copper ions from aqueous solution by adsorption was investigated. The methods were applied to removal of copper in artificial water and drinking water samples using activated carbon. For this purpose, metal removal from water depends on the pH, initial concentration of metal, amount of activated carbon, and effect of sorption time were investigated. The process parameters were investigated with batch studies. In this study, commercial activated carbon, Chemviron C-1300, has been used. Granular activated carbon were characterized using nitrogen porosimetry, pH titration, Boehm's titration, mercury porosimetry, FTIR and scanning electron microscope measurements. The copper ions were determined by an atomic absorption spectrometry. Optimum conditions were found as concentration of 10 mg l^-1, pH: 5, contact time:25 min, and activated carbon amount:750 mg. Optimum condition were applied to drinking water for removal of Cu(II). Furthermore, adsorption isotherm data were fitted to both Langmuir and Freundlich models for finding the optimum conditions.

The construction and performance characteristic of a potentiometric PVC membrane sensor for the determination of triphenyltetrazolium chloride (TPTCl) is described. The sensor is based on the use of triphenyltetrazolium (TPT)-tetraphenylborate (TPB) ion pair as ion exchange sites in PVC matrix in presence of dioctylphathalte as plasticizer. The TPT membrane sensor shows a stable, near-Nernestian response for 6×10^-6 - 1×10^-2 M TPTCl at 25 °C over the pH range 3-10 with cationic slope of 57.0 ± 0.5. The lower detection limit is 4×0^-6M and the response time is 10-30 sec. Selectivity coefficients for TPTCl relative to a number of different cations and anions were investigated, which there is negligible interferences. However, iodide, bromide and thiocyanate were interfering. The determination of 2.0- 3340.0 μg/ml of TPTCl in aqueous solutions shows an average recovery of 98.5 % and a mean relative standard deviation of 1.9 at 160μg/ml. The proposed method has been used for indirect potentiometric determination of ascorbic acid in its pharmaceutical formulations which are comparable favorably with those of British pharmacopoeia method. Precipitation titrations involving TPTCl as titrant are monitored with NaTPB using the proposed membrane sensor; the inflection break is about 300 mV.

A flotation method based on formation of an ion-associate complex between ferroin and Pb(II)-thiosulfate complex is proposed for the quantitative separation and preconcentration of Pb(II) content in various environmental samples. The flotation process was carried out using a 250-mL aliquot of the aqueous solution at the buffering pH of 8.50 in which the ion-associate complex was floated at the interface of the aqueous/xylene phases. The ion-associate complex was then dissolved in 5 mL of acidic solution of 0.05 M KClO₃ and the Pb(II) content was determined by flame atomic absorption spectrometry (FAAS). By this method, a preconcentration factor of 50 can be achieved so that the determination of trace amounts of Pb(II) ions is feasible in the range of 1×10^-7 to 1.2×10^-6 M. The LOD and RSD (n=7) were obtained as 1.5×10^-8 M and 1.5 %, respectively. It was found that a large number of cations and anions even at high considerably foreign ion/Pb(II) ratios were not interfered. In treatment with a SRM water sample and a synthetic liquid extract of vegetable, the recoveries were more than 95 %s, which confirmed validity of the method. The method was satisfactorily applied for determining of trace amount of Pb(II) in some complex matrices.

Conditions have been developed for simultaneous determination of paraquat (PQ) and diquat (DQ) by capillary zone electrophoresis (CZE) with diode array detector (DAD) after their preconcentration by solid phase extraction using Megabond Elut C18 and Strata X 33 μm Polymeric sorbent cartridges. Conditions were optimised with reference to pH, EDTA concentration in sodium acetate acetic acid buffer of pH (3.8) with 3-8 % of methanol, ethanol and acetonitrile as organic modifier in the background electrolyte. UV detection with variable wavelength was used to determine each compound at its maximum absorption providing an excellent sensitivity. The recovery of these compounds from water samples spiked at different levels was more than 90 %. The limit of detection (S/N=3) obtained for milli-Q water when spiked with standards was 0.17 ppm for DQ and 0.19 ppm for PQ, in tap water samples it was found to be 0.27 ppm for DQ and 0.31 ppm for PQ, in cola beverages it was found to be 0.29 ppm for DQ and 0.35 ppm for PQ, and for the urine samples it was 0.36 ppm for diquat and 0.41 ppm for the PQ without preconcentration. After preconcentration using polymeric cartridge the detection limit was reduced to 2.5 ppb for DQand 3 ppb for PQ for the milli-Q water. These detection limits allows for the analysis of these compounds at the levels established by the US Environmental Protection agency.