Annali di chimica最新文献

The present work reports analytical results relevant to voltammetric determination of Pt(II), Pd(II), Rh(III) [Platinum Group Metals (PGMs)] and Pb(II) in superficial water sampled in sites differently influenced by vehicle traffic, especially considering their temporal behaviour. For all the elements, in addition to detection limits, precision, expressed as relative standard deviation (s_r %) and accuracy, expressed as percentage recovery (R %) are also reported. In all cases they show to be good, being the former lower than 6 % and the latter in the range 94-105 %. A critical comparison with spectroscopic measurements is also discussed.

A sensitive and simple method for the simultaneous preconcentration of nutritionally important minerals in real samples has been reported. The method is based on the adsorption of Cu²⁺, Ni²⁺, Co²⁺ and Pb²⁺ on 4-propyl-2-thiouracil (PUT) loaded on activated carbon. The metals on the complexes are eluted using 5 mL 3 M HNO₃ in acetone. The influences of the analytical parameters including pH and sample volume were investigated. The effects of matrix ions on the retentions of the analytes were also examined. The recoveries of analytes were generally higher than 95 %. The detection limits for Cu²⁺, Ni²⁺, Co²⁺ and Pb²⁺ were 1.6, 1.3, 1.2, 2.3 ng ml^-1, respectively. The method has been successfully applied for these metals content evaluation in some real samples including natural water samples.

A new electrode was modified by multilayer films composed of heteropolyanion (SiW₁₂) and cationic polymer poly(diallyldimethylammonium chloride) through electrochemical growth. The modified electrode electrochemical behavior, the effect of solution pH and electrocatalytic response to the reduction of BrO₃^- and NO₂^- have been investigated. The result shows that the electrochemical process of multilayer films modified electrode including SiW₁₂ is a reversible process by electrochemical step. One-electron process has no proton participation in the first step, and one-electron process is accompanied by one proton participation in the second step and two-electron process is accompanied by two protons participation in the third step. The films grow uniformly, and the peak currents increase with increasing layer numbers. The peak currents increase with scan rate, and the reduced potentials of multilayer films shift negatively with increasing pH. The electrochemical mechanism of multilayer films was suggested.

The results of an experimental analysis carried out to investigate PM_2.5 concentration levels and the content of polycyclic aromatic hydrocarbons, as well as inorganic trace elements in the atmospheric particles are presented. Measurements were taken with a micrometeorological station equipped with an optical PM_2.5 detector, and simultaneously, particles were collected on filters for subsequent chemical analyses. The average value of daily PM_2.5 concentration is 21.5 ug/m3 and real-time measurements indicate that the average concentration during the day (8 am to 8 pm) is about 25 % lower than the nocturnal average. Short-time averages of PM_2.5 decrease when the wind speed increases as consequence of the more efficient mixing. Meteorological measurements indicate the presence of a local daily (breeze) circulation with wind blowing from the Alps or the Adriatic Sea and, during this circulation, larger concentrations were observed, with wind coming from the Alps. Days of high PM_2.5 concentration with dominant anthropic or with prevalent crustal contributions were identified.

Regarding trace metals, their average concentrations are comparable to those found in others urban areas, except for Cd (3 ng m^-3), probably due to the presence of glass-works in Murano. The highest concentrations are observed for K (99 ng m^-3) and Na (73 ng m^-3), which are the main constituents of marine spray, while the lowest concentrations are observed for elements such as Cs and Co (respectively 0.01 and 0.02 ng m^-3). Also the concentrations of PAH are comparable with those of other industrial areas, as their sum ranges from 0.16 ng m^-3 to 3.73 ng m^-3, but if considered as B(a)P toxicity equivalent, they are largely lower (0.036±0.026 ng m^-3). From the analyses of discriminating ratios, it has been found that the main origin of PAH in PM_2.5 samples may be petrogenic, probably related to the presence of refinery and petrochemical plants on the mainland, although the contribution of combustion processes cannot be excluded.

Aminylferrocene(FcAI)-Nanogold(NG) modified glassy carbon electrode (FcAI/NG/GCE) was prepared by the Au-N bond between Au and FcAI. Electrochemical impedance spectroscopy (EIS) was employed to study the surface of the modified electrode. The electrochemical behavior of dopamine (DA) on the modified electrode was investigated and it was found that the modified electrode had an obvious electrocatalytic effect on DA. Compared with a bare GCE, the modified electrode exhibited an apparent shift of the oxidation peak potential in the negative potential direction and a marked enhancement in the current response for DA. We investigated the determination of DA on the modified electrode by differential pulse voltammetry (DPV). Linear calibration curve was obtained in the range of 7.0×10^-7 mol/L to 6×10^-4 mol/L of DA in 0.1mol/L phosphate buffer solution (pH= 7.0) with a correlation coefficient of 0.9989. The detection limit (S/N=3) of DA was estimated to be 1.0×10^-7 mol/L. Especially, by using the modified electrode, we can separate the oxidation peaks of ascorbic acid (AA) and DA in the PBS and it was satisfactory for the determination of DA with the interference of AA.

The development of a network to monitor surface waters is a critical element in the assessment, restoration and protection of water quality. In this study, concentrations of 42 pesticides – determined by GC-MS on samples from 11 points along the Ferrara area rivers – have been analyzed by chemometric tools. The data were collected over a three-year period (2002-2004). Principal component analysis of the detected pesticides was carried out in order to define the best spatial locations for the sampling points. The results obtained have been interpreted in view of agricultural land use. Time series data regarding pesticide contents in surface waters has been analyzed using the Autocorrelation function. This chemometric tool allows for seasonal trends and makes it possible to optimize sampling frequency in order to detect the effective maximum pesticide content.

For the first time, a novel, simple and reliable method for analysis of pymetrozine residues in flue-cured tobacco leaves has been developed utilizing HPLC-UV with liquid-liquid partition cleanup. Pre-treatment with ultrasonic extraction and liquid-liquid partition procedures gave preferable baseline separation and clean chromatograms by removing water-soluble and fat-soluble components which interfere with pymetrozine in the test. The performance of the method was evaluated and validated: the detection limit (LOD) was 0.005μg.mL^-1, the relative standard deviation (RSD) was 1.2 % (n=5), and the overall recovery was above 90 % at fortification levels of 0.200, 0.500, 1.000, and 5.000 mg.kg^-1. The proposed method was successfully employed for the determination of pymetrozine residues in twelve flue-cured tobacco samples collected from different regions of China.

The present study was carried out in a batch system using a lichen (Pseudevernia furfuracea (L.) Zopf) for the sorption of nickel(II) and copper(II) ions from water. Particularly, the effect of pH, contact time and temperature were considered. Pseudevernia furfuracea exhibited nickel(II) and copper(II) uptake of 49.87 and 60.83 mg/g at an initial pH of 4 and 5-6 at 35 °C respectively. Both the Freundlich and Langmuir adsorption models were suitable for describing the biosorption of nickel(II) and copper(II) by the biosorbent. Biosorption showed pseudo first order rate kinetics for nickel and copper ions. Using the equilibrium constant values obtained at 25 and 35 °C, the thermodynamics properties of the biosorption (ΔG°, ΔH° and ΔS°) were determined. The biosorption of nickel(II) and copper(II) onto Pseudevernia furfuracea was found to be endothermic.

The simultaneous determination of manganese(II) and iron(II) mixtures by using spectrophotometric methods is a difficult problem in analytical chemistry, due to spectral interferences. By multivariate calibration methods, such as partial least squares (PLS), it is possible to obtain a model adjusted to the concentration values of the mixtures used in the calibration range. Orthogonal signal correction (OSC) is a preprocessing technique used to remove the information unrelated to the target variables based on constrained principal component analysis. OSC is a suitable preprocessing method for partial least squares calibration of mixtures without loss of prediction capacity using spectrophotometric method. In this study, the calibration model is based on absorption spectra in the 450-600 nm range for 21 different mixtures of manganese(II) and iron(II). Calibration matrices were containing 0.05-1.2 and 0.1-2.3 μg mL^-1 Mn(II) and Fe(II), respectively. The RMSEP for manganese(II) and iron(II) with OSC and without OSC were 0.0316, 0.0291, and 0.0907, 0.115, respectively. This procedure allows the simultaneous determination of manganese(II) and iron(II) in synthetic and real matrix samples with good reliability of the determination.