[en] In this paper the results of a potentiometric (ISE-[H⁺] glass electrode) investigation at t = 25 0^C on the complexing ability of phytate towards trimethyltin(4) (tmt) and on the acid-base properties of tmt at high metal concentration (0.050 and 0.075 mol L^-1) are reported. First we determined the hydrolytic constants of tmt in aqueous solution without further addition of background salt (self medium); in these experimental conditions we verified the formation of the following hydrolytic species: tmt(OH)⁰, tmt(OH)₂^- and the binuclear species (tmt)₂(OH)⁺. Successively, we studied the complex formation constants obtained from the interaction of phytate anion with tmt in the same experimental conditions of hydrolytic measurements; the speciation model obtained takes into account several polynuclear species (tmtH₅Phy⁶-; tmt₂H₅Phy⁵-; tmt₃H₄Phy^5-; tmt₃H₅Phy^4-; tmt₄H₆Phy^2-; tmt₅HPhy^6-). A comparison with literature data is reported too

[en] Trans-3-(3-pyridyl) acrylic acid (PAA) was deposited on glassy carbon electrode (GCE) by electro polymerization in pH 7.0 phosphate buffer solution (PBS). The poly (3-(3-pyridyl) acrylic acid) (PPAA) film modified glassy carbon electrode shows an excellent electrochemical response for dopamine (DA), ascorbic acid (AA) and uric acid (UA). The cyclic voltammetry oxidation peaks for DA and AA, DA and UA, AA and UA are separated by 150 mV, 130 mV and 280 mV, respectively. This permits the simultaneous determination of AA, DA and UA. The interference of AA with the determination of DA could be eliminated because of the electrostatic interaction between DA cations and the negatively charged PPAA film at pH 7.0. The anodic peak currents of DA, AA and UA increase linearly with concentration in the range of 1-40 μmol L^-1, 10-400 μmol L^-1 and 1.6-80 μmol L^-1, respectively, with a correlation coefficient (r) always higher than 0.998. The detection limit is 0.06 μmol L^-1, 0.8 μmol L^-1 and 1.1 μmol L^-1 for DA, AA and UA, respectively

[en] A model was developed to predict the steady-state [·OH] in the surface layer of natural waters as a function of nitrate, inorganic carbon (IC) and dissolved organic matter (DOM). The parameter values were studied in the range detected in shallow high-mountain lakes, to which the model results are most relevant. Calculations indicate that [·OH] increases with increasing nitrate and decreasing IC, and conditions are also identified where [·OH] is directly proportional, inversely proportional or independent of DOM. Based on the model results it is possible to predict the half-life time, due to reaction with ·OH, of given dissolved compounds, including organic pollutants, from the water composition data

[en] The chromium, cobalt and lead removal from aqueous solution by natural and modified zeolites was examined by using a batch-type method. Clinoptilolite samples used in this study were supplied from Bigadic, Turkey. All samples were modified with HNO₃ or NaOH to improve the adsorption capacity for heavy metals. The removal efficiencies and kinetics of heavy metals such as chromium, cobalt and lead on natural and modified zeolites were determined. The effects of the initial metal concentration on the removal percentage of heavy metal ions were studied. Freundlich and Langmuir isotherm constants and correlation coefficients were found and the equilibrium process was described by the Freundlich isotherm. The adsorption kinetic was tested and then it indicates the process to be diffusion controlled

[en] An investigation on the partitioning of naphthalene and phenanthrene between water and some water-insoluble phases has been carried out by Uv-vis-NIR spectrophotometry. The analysis of the experimental results emphasized the role of intermolecular interactions and structural features of the hosting phases as driving forces of the partitioning of these polycyclic aromatic hydrocarbons. The critical comparison of the resulting distribution constants allowed to evaluate the potentials of some extracting phases to set up sensitive analytical methods and/or effective environment remediation technologies

[en] A new flow injection chemiluminescence (CL) system was used for the determination of noscapine. This technique is based on the reduction effect of noscapine on the Ru(phen)₃³⁺, which is produced by reaction between Ru(phen)₃²⁺ and acidic Ce(4) solutions, and this rapid reduction produces strong CL. Calibration plots were linear over the range of 3.0x10^-7-2.0x10^-6 mol L^-1 and 2.0x10^-6-2.0x10^-4 mol L^-1. The CL intensity was so high, that it is able to produce a detection limit of 6.6x10^-8 M noscapine (3σ). The relative standard deviation of 2.0x10^-6 M noscapine was 1.0% (n=10). The proposed method was successfully applied for the flow injection determination of noscapine in cough and Tonin syrup samples. The results of real sample analyses show good recovery percentages (97.3-102.4%). The minimum sampling rate was 100 samples per hour

[en] A new ultraviolet spectrophotometric method has been developed for the direct qualitative determination of captopril in pharmaceutical preparation and biological fluids such as human plasma and urine samples. The method was accomplished based on parallel factor analysis (PARAFAC) and partial least squares (PLS). The study was carried out in the pH range from 2.0 to 12.8 and with a concentration from 0.70 to 61.50 μg ml^-1 of captopril. Multivariate calibration models PLS at various pH and PARAFAC were elaborated from ultraviolet spectra deconvolution and captopril determination. The best models for this system were obtained with PARAFAC and PLS at pH = 2.04 (PLS-PH2). The applications of the method for the determination of real samples were evaluated by analysis of captopril in pharmaceutical preparations and biological (human plasma and urine) fluids with satisfactory results. The accuracy of the method, evaluated through the root mean square error of prediction (RMSEP), was 0.58 for captopril with PARAFAC and 0.67 for captopril with PLS-PH2 model. Acidity constant of captopril at 25 0^C and ionic strength of 0.1 M have also been determined spectrophotometrically. The obtained pK_a values of captopril are 3.90 ± 0.05 and 10.03 ± 0.08 for pK_a1 and pK_a2, respectively

[en] A highly selective, sensitive and rapid method for the determination of trace amounts of inorganic mercury based on the reaction of Hg (2) with 6-mercaptopurine and the solid phase extraction of the complex on C₁₈ membrane disks was developed. The 6-mercaptopurine selectively reacts with Hg (2) to form a complex in the pH range of 5-8. This complex was preconcentrated by solid phase extraction with C₁₈ disks. An enrichment factor of 100 was achieved. The molar absorptivity of the complex is 0.26 x10^-6 L. mol^-1. cm^-1 measured at 315 nm. The Beer's law is obeyed in the concentration range of 0.002 - 0.048 μg mL^-1. The relative standard deviation for eleven-replicated measurement of 0.04 μg mL^-1 is 1.5 %. The detection limit is 0.001 μg mL^-1 in the water samples. The advantage of the method is that the determination of Hg (2) is free from interference of almost all the cations and anions found in environment and wastewater samples. The determination of Hg (2) in water samples of different origins and marine sediment were carried out by the present method and cold vapor atomic absorption spectrometry (CVAAS). Also the method's accuracy was investigated by using SRM 2709. The obtained results by the present procedure were in good agreement with those of the CVAAS and certified value, so that the applicability of the proposed method was confirmed for the real samples

[en] The formal redox potential of the Ti(4, 3) couple has been determined at 25 0^C in 1 M HCl, 2 M NaCl aqueous medium, by emf measurements of a junction-free cell with glass and mercury electrodes. Ti(3) and Ti(4) concentrations were changed by controlled electrolysis. The mean value of the searched formal potential, in a large range of total titanium concentration, is 9 ± 1 mV against the molar hydrogen electrode in the same ionic medium

[en] A very sensitive, simple and selective spectrophotometric method for simultaneous determination of phosphate and silicate based on formation of phospho- and silico molybdenum blue complexes in the presence of ascorbic acid is described. Although the complexes of phosphate and silicate with reagent in the presence of ascorbic acid show a spectral overlap, they have been simultaneously determined by principal component artificial neural network (PC-ANN). The PC-ANN architectures were different for phosphate and silicate. The output of phosphate PC-ANN architecture was used as an input for silicate PC-ANN architecture. This modification improves the capability of silicate PC-ANN model for prediction of silicate concentrations. The linear range was 0.01-3.00 μg mL^-1 for phosphate and 0.01-5.00 μg mL^-1 for silicate. Interference effects of common anions and cations were studied and the proposed method was also applied satisfactorily to the determination of phosphate and silicate in detergents