Publications

Abstract The differential capacity of a large number of liquid-liquid interfaces has been determined by impedance spectroscopy. Even in the absence of ion pairing, the interfacial capacity was always larger than predicted by Gouy-Chapman theory. These findings are explained within a simple model, in which an extended mixed-boundary layer exists at the interface, whose thickness extends over several solvent diameters.

Abstract A fixed analytical window of observation, 5 mu mol l(-1) free copper and 100 mu mol l(-1) total copper, but methods different in nature, operation mode and time scale were applied, in parallel, at pH 6.50 and 16 degrees C, to solutions with copper complexes of very different thermodynamic stabilities. Ethylenediaminetetraacetic acid (EDTA), L-cysteine, L-lysine, L-proline and succinate were used as metal buffers. Chitin (batch and column modes), chelex-100 (column mode) and normal pulse anodic stripping voltammetry (NPASV, -0.3 V deposition potential) were used as techniques. A strategy, based on using the mass of polymer that provided uptake of free copper similar to that taken up by Pseudomonas syringae bacterial cells in absence of ligands, was used for all but NPASV methods. Flame atomic absorption spectrophotometry was used for metal detection. The lability of copper complexes with simple organic ligands showed a strongly operational character. The time scale of the physicochemical method used for the determination of lability was not the only parameter inherent to the method that influenced the extent of copper complex dissociation. The nature of both initial and competing ligands and the operation mode may also condition the speciation results.

Abstract The standard (p(o) = 0.1 MPa) enthalpies of formation Delta(f)H(m)(o)(cr) at the temperature T = 298.15 K were determined using static-bomb calorimetry for crystalline 5-methoxybenzofurazan (5MeOBFN), 5-methoxybenzofurazan-1-oxide (4MeOBFNO), 5-methylbenzofurazan-1-oxide (5MeBFNO), and 4-nitrobenzofurazan-1-oxide (4NO(2)BFNO); using rotating-bomb calorimetry for 5-chlorobenzofurazan-1-oxide (5CIBFNO). The standard enthalpies of sublimation Delta(cr)(g)H(m)(o) at T = 298.15 K were measured by microcalorimetry and, from the enthalpies of formation of the gaseous compounds, the dissociation enthalpies D-m(o) of the (N+-O-) dative covalent bonds were derived.

Abstract A fully automated flow injection analysis (FIA) dilution system bared on the Zone sampling technique is described. The system relies on the use of a PC-compatible microcomputer for instrumental control and data acquisition and processing. The computer controls two rotatory valves which select different portions of the injected sample plug and then are re-sampled toward the detector. The system automatically chooses a suitable dilution factor for each sample. The dilution system was coupled to an atomic absorption spectrometer and to a flame photometer for the determination of Ca, Mg, Na, K, Cu, Sn and Fe in highly concentrated water samples. The methodology affords up to 10 000-fold dilution factors with good precision (RSD < 3%) and high sampling rates (never lower than 90 determinations per hour).

Abstract The simultaneous torsion and mass-loss effusion technique was used to measure the vapour pressure of the crystalline complexes of iron(III) with pentane-2,4-dione (HACAC) and with 2,2,6,6-tetramethylheptane-3,5-dione (HDPM), as a function of temperature, from T = 369.3 K to T = 387.5 K and from T = 359.8 K to T = 377.8 K, respectively. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation at the mean temperature of the experimental temperature ranges, were derived for both complexes. The mean values obtained from both techniques are: for Fe(ACAC)(3), Delta(cr)(g)H(m) degrees (377.8 K)/(kJ . mol(-1)) = (124.6+/-0.9); and for Fe(DPM)(3), Delta(cr)(g)H(m) degrees(377.8 K)/ (kJ . mol(-1)) = (125.8+/-0.9). Using the estimated value of Delta(cr)(g)C(p,m)degrees = -50 J . K-1. mol(-1), for both complexes, the standard molar enthalpies of sublimation at T = 298.15 K, Delta(cr)(g)H(m) degrees (298.15 K)/(kJ . mol(-1)), were estimated as (128.6+/-0.9) and (129.3+/-1.2), respectively. From the standard molar enthalpies of formation of the gaseous complexes, the mean molar (Fe-O) bond dissociation enthalpies were derived. (C) 1996 Academic Press Limited

Abstract The interactions between UO22+ and fulvic acids (FUA) mere studied by a methodology that involves synchronous molecular fluorescence spectroscopy, to monitor the quenching of the intrinsic fluorescence of FUA by UO22+, and a self-modelling mixture analysis method (SIMPLISMA), to treat spectroscopic data, This methodology was applied to the analysis of the interaction of UO22+ with salicylic acid at pH 3.5 and with a soil FUA at pH 3.5 and 7.0, in this case in the presence of various concentrations of carbonate ion (10(-5), 10(-4) and 10(-3) mol l(-1)), From the calculated quenching fluorescence intensity profiles, using either the Stern-Volmer relationship or a non-linear least-squares method, mean conditional stability constants (log values with standard deviations in parentheses) were estimated for salicylic acid [respectively 2.72(4) and 2.77(6)], for FUA at pH 3.5 [3.93(2) and 4.4(1)] and pH 7.0 [4.06 and 4.1 (average values for the various concentrations of carbonate ion)l. The non-linear least-squares method also allowed the estimation of the number of binding sites that exist in FUA (0.11 and 0.24 mol g(-1) at pH 3.5 and 7.0, respectively).

Abstract The interaction of the beryllium ion [Be(ll)] with one of the major constituent of soil organic matter, fulvic acids (fua), was investigated. The complexation of Be(ll) by two samples of fua (amph and gran), at a concentration of 80 mg/L, was monitored by synchronous fluorescence spectroscopy at four pH values (4, 5, 6, and 7). A self-modeling curve resolution technique (evolving factor analysis) was used in the analysis of the sets of spectra collected at increasing Be(ll):fua ratio to obtain concentration profiles that ideally correspond to one type of binding site. These profiles were adjusted to a 1:1 complexation model. Quite strong complexation of Be(ll) by fua occurs at nearly neutral pH (6-7) (logarithm of the conditional stability constant between 5.6 and 6.5), indicating that fua probably affect markedly the mobility of Be(ll) in the environment.

Abstract The major binding sites for Al(III) in six samples of fulvic acids (fua) extracted form soils and leaf litters were investigated by synchronous fluorescence (SyF) spectroscopy. Two samples of fua from soil of an oak forest (two horizons, 0-5 cm, fuaol, and 5-15 cm, fuao2) and four fua like samples extracted from leaf litters (eucalyptus, fern, oak and chestnut coverture, respectively feu, fer, foa and fch) were studied. The SyF spectra of the mixtures of fua and increasing concentration of Al(III), at pH 4, were analyzed by evolving factor analysis (EFA), a self-modeling curve resolution method, to detect the number of major binding sites, their SyF spectra and SyF profiles as function of the AI(III) concentration. The overall set of calculated SyF spectra was analyzed by pattern recognition methods, such as cluster analysis and multidimensional scaling, to detect similarities and differences between them. Although there are differences in the intrinsic SyF properties of fua extracted from soils and leaf litters, the soil fua samples showing a more complex binding site composition, the most important binding site is common to all fua samples studied. The amount of this binding site was roughly estimated. It is approximately the same for all samples but for fuao2, in which the amount is twice the others.