Publications

Abstract A method involving solid-phase micro extraction ( SPME) and gas chromatography with electron capture detection (SPME-GC-ECD) has been optimised for identification and quantification of 2,4,6-trichloroanisole (TCA) at ng L-1 concentrations in disinfected ( chlorinated) water samples. A central composite design was used for factorial analysis of four factors, three factors related to the SPME (PDMS fibre) procedure ( adsorption time, temperature of the sample during headspace sampling, and desorption time) and one related to the GC operation ( the rate of increase of the temperature of the GC oven). Good linearity ( linear correlation coefficient greater than 0.999) was observed for TCA concentrations up to 50 ng L-1, limits of detection and quanti. cation of 0.7 and 2.3 ng L-1, respectively, and good precision ( relative standard deviation 2.8% and 3.4% for 5 and 30 ng L-1 of TCA, respectively). Besides TCA, this system also enables the detection and quanti. cation of the four trihalomethanes in the mu g L-1 concentration range with limits of detection and quanti. cation of approximately 0.3 mu g L-1 and 1 mu g L-1, respectively.

Abstract Olives from three cultivars (Olea europaea Cv. Cobrancosa, Madural and Verdeal Transmontana) were subject to a biometric characterization of the fruit and endocarp. Olives were harvested in a selected olive grove, where the three cultivars are present, guaranteeing the homogeneity of the pedologic and climate conditions. Five trees from each cultivar, to a total of 15 trees, and 40 olives for each tree were picked up, to a total of 200 olives per cultivar. Each olive was characterized by 26 fruit and endocarp parameters as recommended by Conseil Oleicole Internationale (COI). A linear discriminant analysis was performed in order to assess the discrimination capacity of the measurement parameters between the three cultivars. An almost full discrimination of the olives from different cultivars was only achieved when fruit and endocarp, data was analyzed together.

Abstract Excitation-emission matrices (EEM) of fluorescence of aqueous solutions of humic substances (HS), and sets of EEM acquired as function of the HS concentration, were analysed by multivariate curve resolution alternating least squares (MCR-ALS). Three types of HS samples were studied: one commercial humic acid; two samples of fulvic acid (FA) extracted from a pinewood soil; two samples of FA extracted from recycled wastes. The fluorescence measurements were carried out at HS concentration between 5 and 100 mg/L and at pH 6. The application of MCR-ALS algorithm on each individual EEM, as well as on column-wise augmented matrices, allows the identification of three major fluorophores in all HS samples analysed. The emission and excitation spectra of these fluorophores were recovered and are characteristic of each sample. Moreover, the variation of the fluorescence intensities of each fluorophore with HS concentration shows deviations from linearity at HS concentration higher than 30 mg/L, depending on the fluorophore and/or sample. This behaviour reveals the existence of inner filter effects that affect the proportionally between the fluorescent signal and concentration but do not provoke measurable distortions on the fluorescence spectra of the detected fluorophores.

Abstract Radical anions of o-, m-, and p-benzoquinone were produced in a Fourier transform mass spectrometer by low energy electron attachment or collision-induced dissociation and were differentiated. Classical derivatization experiments also were carried out to authenticate the ortho and meta anions. Gas-phase techniques were used to measure the proton affinities of all three radical anions and the electron affinities of o- and m-benzoquinone. By combining these results in thermodynamic cycles, we derived heats of hydrogenation of o-, m-, and p-benzoquinone (Delta(hyd)H degrees(1o, 1m, and 1p) = 42.8 +/- 4.1, 74.8 +/- 4.1, and 38.5 +/- 3.0 kcal mol(-1), respectively) and their heats of formation (Delta(t)H degrees(1o, 1m, and 1p) = -23.1 +/- 4.1, 6.8 +/- 4.1, and -27.7 +/- 3.0 kcal mol-1, respectively). Good accord with the literature value for the para derivative was obtained. Combustion calorimetry and heats of sublimation also were measured for benzil and 3,5-di-tert-butyl-o-benzoquinone. The former heat of formation agreed with previous determinations, while the latter result (Delta(f)H degrees (g) = -73.09 +/- 0.87 kcal mol(-1)) was transformed to Delta(f)H degrees(1o) = -18.9 +/- 2.2 kcal mol(-1) by removing the effect of the tert-butyl groups via isodesmic reactions. This led to a final value of Delta(f)H degrees) = -21.0 +/- 3.1 kcal mol(-1). Additivity was found to work well for m-benzoquinone, but BDE1 and BDE2 for 1,2- and 1,4-dihydroxybenzene differed by a remarkably small 14.1 +/- 4.2 and 23.5 +/- 3.7 kcal mol(-1), respectively, indicating that o- and p-benzoquinone should be excellent radical traps.

Abstract The standard (pdegrees = 0.1MPa) molar enthalpies of formation for 2-, 3- and 4-cyanophenol in the gaseous phase were derived from the standard molar enthalpies of combustion in oxygen at T D 298: 15 K, measured by static bomb combustion calorimetry, and the standard molar enthalpies of sublimation at 298.15 K, measured by Calvet microcalorimetry: 2-cyanophenol, (32.8 +/- 2.1) kJ-mol(-1); 3-cyanophenol, (37.8 +/- 2.2) kJ-mol(-1); 4-cyanophenol, (35.1 +/- 2.5)-kJ-mol(-1). Ab initio geometry optimizations of the three cyanophenols and respective phenoxyl radicals and phenoxide anions were performed using the 6-31G* basis sets. Single-point MP2 and DFT energy calculations allowed the estimation of the enthalpies of formation in the gaseous phase, the O-H bond dissociation energies, and the gas-phase acidities of the three cyanophenols. The theoretical results are generally in good agreement with the experimental findings.

Abstract The permeability of a self-assembled polyelectrolyte multilayer to small ions under the influence of an applied potential difference is studied as a function of the number of layers and the nature of the supporting electrolyte. The multilayer is described as a series of homogeneously charged membranes with alternating sign of their fixed charge. Ion transport is described on the basis of the diffusion equation and the assumption of (Donnan) electrochemical equilibrium at the boundaries between layers. The calculated steady-state current-voltage curves are found to be in good agreement with experimental linear sweep voltammograms (at low sweep rate). The permeability of polystyrenesulfonate/polyallylamine multilayers to ferro/ferricyanide ions is found to decrease monotonically with increasing number of layers when sodium perchlorate is used as the supporting electrolyte. However, an interesting non-monotonic dependence on the number of layers is observed when the supporting electrolyte is barium perchlorate. Both types of behaviour are accounted for satisfactorily by the theoretical model.

Abstract The standard (pdegrees = 0.1 MPa) molar enthalpy of formation of crystalline 2H-1,3-benzoxazine-2,4(3H)dione was measured, at T = 298.15 K, by static bomb calorimetry and the standard molar enthalpy of sublimation, at T = 298.15 K, was obtained using Calvet microcalorimetry. These values were used to derive the standard molar enthalpy of formation in the gaseous phase, T = 298.15 K, of -(401.0 +/- 3.5) kJ mol(-1). The standard molar enthalpy of sublimation of isatoic anhydride was recalculated, and our recommended experimental value for the standard molar enthalpy of formation in the gaseous phase, T = 298.15 K, is -(406.2 +/- 3.4) kJ mol(-1). Density functional calculations for the two isomers 2H-1,3-benzoxazine-2,4(3H)dione and isatoic anhydride, in which the ring nitrogen and oxygen have been transposed, confirm the experimental evidence of nearly identical thermochemical stability for these isomers.

Abstract The assisted transfer of silver ion, Ag+, by complexation of Ag+ with the tetrakis(4-chlorophenyl)borate (TPBCl-) anion was studied at the interface between two immiscible electrolyte solutions (ITIES). The elucidation of the interfacial mechanisms employed the cyclic voltammetry technique applied to macro and micro liquid/liquid interfaces. This procedure allowed to identify Ag+ as the species which is transferred at the liquid/liquid interface and also the formation of an 1:2 metal:ligand complex when TPBCl- is in excess. The value for the formal transfer potential of silver(I) from aqueous to 1,2-dichloroethane was evaluated and the association constant for the [Ag(TPBCl)(2)](-) complex was determined.