Annali di chimica最新文献

Trans-3-(3-pyridyl) acrylic acid (PAA) was deposited on glassy carbon electrode (GCE) by electropolymerization 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.

A highly selective, sensitive and rapid method for the determination of trace amounts of inorganic mercury based on the reaction of Hg (II) with 6-mercaptopurine and the solid phase extraction of the complex on C₁₈ membrane disks was developed. The 6-mercaptopurine selectively reacts with Hg (II) 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 ×10^-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 (II) is free from interference of almost all the cations and anions found in environment and wastewater samples. The determination of Hg (II) 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.

A very sensitive, simple and selective spectrophotometric method for simultaneous determination of phosphate and silicate based on formation of phospho- and silicomolybdenum 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.

In this paper the results of a potentiometric (ISE-[H⁺] glass electrode) investigation at t = 25 °C on the complexing ability of phytate towards trimethyltin(IV) (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 (tmtH₅Phy^6-; tmt₂H₅Phy^5-; tmt₃H₄Phy^5-; tmt₃H₅Phy^4-; tmt₄H₆Phy^2-; tmt₅HPhy^6-). A comparison with literature data is reported too.

Fragments of wall paintings from Istria, coming from the Basilica of Guran near Vodnjan, from the cemeterial Church of Saint Simeon in Guran and from the Benedictine monastery of Santa Maria Alta near Bale were studied.

The analytical instrumental techniques used were Optical Microscopy, Scanning Electron Microscopy equipped with an EDS microanalysis detector, X Ray diffraction, FTIR infrared Spectroscopy and Raman Spectroscopy.

Red and yellow pigments used in Guran and Bale have bean derived from red and yellow istrian bauxites, as already demonstrated for works from 11^th to 15^th century.

The blue pigment found in the paintings of the Bale Chapel is a lapislazzuli blue; this fact confirms the literature data referring to the period from 11^th to the 16^th century.

The materials and pigments used at Bale and Guran fit with the Istrian tradition and history of painting going back to the first Carolingian period.

The construction and general performance of novel potentiometric membrane ion selective electrodes for determination of papaverine hydrochloride has been described. They are based on the formation of the ion association complexes of papaverine (PA) with tetraphenylborate (TPB)(I) or tetrathiocyanate (TTC)(II) counter anions as electro-active material dispersed in a PVC matrix. The electrodes show fast, stable, near Nernstian response for 1×10^-2 to 6×10^-5 M and 1×10^-2 to 1×10^-5 M for PA-TPB and PA-TTC respectively at 25 °C over the pH range of 3-5.0 with a cationic slope of ∼ 56.5±0.5 mV/decade for both sensors respectively. The lower detection limit is 4×10^-5 and 8×10^-6 M for PA- I and PA-II respectively with fast response time ranging from 20-45 sec. Selectivity coefficients for PA relative to a number of interfering substances were investigated. There is a negligible interference from the studied cations, anions, and pharmaceutical excipients. The determination of 4.0-3000.0 μg/ml of PA in aqueous solutions shows an average recovery of 99.1 % and a mean relative standard deviation of 1.4 at 100 μg/ml. The direct determination of PA in some formulations (Vasorin injection) gave results that compare favorably with those obtained using the British Pharmacopoeia method. Potentiometric titration of PA with sodium tetraphenylborate and potassium thiocyanate as titrants utilizing the papaverine electrode as an end point indicator electrode has been carried out.

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.

The preparation of a lead-selective electrode based on bis(1'-hydroxy-2'-acetonaphthone)-2,2'-diiminodiethylamine (L) as sensing material is reported. The plasticized PVC membrane containing 30% PVC, 67% ortho-nitrophenyloctylether (NPOE) and 3% ionophore L was directly coated on a graphite rod. This electrode exhibits a nearly Nernstian slope of 27.8±0.2 mV decade^-1 over a concentration range 10^-6−10^-2 M with a detection limit of 4.0×10^-7 M. The response time of the electrode was found to be <20 s. The potential of the sensor was independent on pH variations in the range 5-7. The selectivity of the electrode towards lead ions over Na⁺, K⁺, Ag⁺, Ca²⁺, Sr²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, La³⁺, Sm³⁺ and Er³⁺ ions was investigated. The prepared electrode was successfully used as an indicator for titration of a lead solution with a standard solution of EDTA. The applicability of the sensor for Pb²⁺ measurement in various synthetic and real samples has been also demonstrated.