Daniela Piazzese

Protonation of carbonate in aqueous tetraalkylammonium salts at 25 °C

Protonation constants of carbonate were determined in tetramethylammonium chloride (Me(4)NCl(aq) 0.1</=I/molkg(-1)</=4) and tetraethylammonium iodide (Et(4)NI(aq) 0.1</=I/molkg(-1)</=1) by potentiometric ([H(+)]-glass electrode) measurements. Dependence of protonation constants on ionic strength was taken into account by modified specific ion interaction theory (SIT) and by Pitzer models. Literature data on the protonation of carbonate in NaCl(aq) (0.1</=I/molkg(-1)</=6) were also critically analysed. Both protonation constants of carbonate follow the trend Et(4)NI>Me(4)NCl>NaCl. An ion pair formation model designed to take into account the different protonation behaviours of carbonate in different supporting electrolytes was also evaluated.

POLYCYCLIC AROMATIC HYDROCARBONS IN SEDIMENTS OF MARINE COASTAL LAGOONS IN MESSINA (ITALY). EXTRACTION AND GC-MS ANALYSIS. DISTRIBUTION AND SOURCES.

The content of 21 polycyclic aromatic hydrocarbons (PAHs) were determined in 16 samples of sediments collected from Ganzirri and Faro marine coastal lagoons in Messina, Italy. Analysis was performed by gas chromatography/mass spectrometry (GC/MS) in selected ion monitoring (SIM) mode. The total concentration of polycyclic aromatic hydrocarbons (ΣPAHs) ranged from 74 to 5755 μg/kg of dry matrix. The resulting distributions and molecular ratios of specific compounds are discussed in terms of sampling location and origin of organic matter. The results obtained show that levels of contamination are not homogeneous throughout the stations, while the relative distributions of PAHs are homogeneous in most of the sampling stations. The organic matter content and PAH concentration were found to be correlated (r = 0.90). It is also shown that the pyrolytic origin is the main source of these compounds in Ganzirri and Faro Lakes sediments.

Polyacrylates in aqueous solution. The dependence of protonation on molecular weight, ionic medium and ionic strength

Abstract The protonation constants of polyacrylates with different molecular weights ( W =2000–750 000 Da) were determined in different ionic media (alkali metal chlorides and nitrates, tetraalkylammonium chlorides), at 25 °C, by potentiometric measurements (H + –glass electrode). Literature data were also considered. Different models used to analyse protonation data were compared: the first was the modified Henderson–Hasselbalch two-parameter equation, and the second was the three-parameter equation proposed by Hogfeldt. The dependence on the ionic strength of the different supporting electrolytes and all the protonation parameters involved in the two models showed the trend Et 4 N + ≫Li + >Na + ≥K + , in accordance with the tendencies of these cations to interact with polycarboxylates. The dependence on molecular weight shows a slightly increasing effect with N (number of monomer units in the polyelectrolyte). Empirical relationships were found for the dependence of the protonation parameters on both ionic strength (I/mol l −1 ) and N. The use of protonation data was considered for polyacrylates in speciation studies, and specific interaction parameters were calculated according to the SIT (Specific Ion Interaction Theory) model.

Inorganic speciation of organotin(IV) cations in natural waters with particular reference to seawater

Abstract This paper examines the inorganic complexing capacity of seawater, where chloride and sulfate ions are present in high concentration, towards mono- di- and tri-organotin(IV) cations which show a different trend of acidity, depending on cation charges, and a corresponding tendency to hydrolysis. By considering hydrolytic species and chloride and sulphate complex formation, a basic inorganic speciation model of organotins in synthetic seawater (Na+, K+, Ca2+, Mg2+, Cl−, SO42−) has been built up. The model has been extended to also consider interactions of organotins with carbonate and fluoride ions, which are other important components of seawater. Because of the strength of hydrolysis processes, the main complexes formed are in general mixed hydroxo-species. No species are formed by organotin cations and/or their hydroxo-species with fluoride owing to their very low concentration in fluoride, in comparison to the other components of seawater. In order to simplify calculations and to establish a cumulative inorganic binding capacity for seawater, we applied a chemical complexation model, according to which the major inorganic components of seawater are considered as a single salt BA.

Sequestering ability of some chelating agents towards methylmercury(II)

AbstractA study on the interactions between CH3Hg+ and some S, N and O donor ligands (2-mercaptopropanoic acid (thiolactic acid (H2TLA)), 3-mercaptopropanoic acid (H2MPA), 2-mercaptosuccinic acid (thiomalic acid (H3TMA)), d,l-penicillamine (H2PSH), l-cysteine (H2CYS), glutathione (H3GSH), N,N′-bis(3-aminopropyl)-1-4-diaminobutane (spermine (SPER)), 1,2,3,4,5,6-benzenehexacarboxylic acid (mellitic acid (H6MLT)) and ethylenediaminetetraacetic acid (H4EDTA)) is reported. The speciation models in aqueous solution and the possible structures of the complexes formed are discussed on the basis of potentiometric, calorimetric, UV spectrophotometric and electrospray mass spectrometric results. For the CH3Hg+–S donor ligand systems, the formation of ML1–z and MLH2–z complex species is observed, together with a diprotonated MLH23–z species for CYS2−, PSH2− and GSH3− and the mixed hydrolytic one ML(OH)−z for TLA2− and MPA2−. The dependence of the stability on ionic strength and on temperature is also analysed. In the other CH3Hg+-L systems (L = MLT6−, SPER and EDTA4−), ML1–z, MLH2–z and MLH23–z complex species are formed, together with the MLH34–z species for SPER, the mixed hydrolytic ML(OH)–z one for SPER and EDTA, and the M2L2–z for EDTA only. On the basis of the speciation models proposed, the sequestering ability of the ligands towards methylmercury(II) cation is evaluated. All S donor ligands show a good sequestering power (at 10−11 mol L−1 level, in the pH range 4 to 8) following the trend MPA2− < PSH2− < GSH3− < TLA2− < CYS2− < TMA3−, while significantly lower is the sequestering ability of MLT, SPER and EDTA (at 10−3–10−5 mol L−1 level, in the pH range 4 to 8). FigureSum of fractions of CH3Hg+-Lz– species (L = S, O and N donor ligands vs. pL

Speciation of low molecular weight carboxylic ligands in natural fluids: protonation constants and association with major components of seawater of oxydiacetic and citric acids

The interaction of oxydiacetate and citrate with the major components of seawater has been studied potentiometrically, at 25C, in an artificial seawater (containing Na C ,K C ,C a 2C ,M g 2C ,C l and SO4 2 ) at different salinities (5‐45 ‰). Apparent protonation constants were calculated, from potentiometric data, and estimated, using an appropriate complex formation model. Formation constants of complexes formed by oxydiacetate and citrate and the cation of seawater (the inorganic content of seawater being considered as a single 1 : 1 salt) were determined. The single salt approximation for the major inorganic components of seawater, which is a good tool in estimating the mean strength of polyanion interaction in seawater, was applied. The comparison of experimental and estimated results showed that a suitable complexation model can be used with reasonable accuracy to predict acid‐base properties of carboxylic ligands in seawater. ©1999 Elsevier Science B.V. All rights reserved.

Speciation of polyelectrolytes in natural fluids Protonation and interaction of polymethacrylates with major components of seawater.

Acid-base properties of two sodium polymethacrylates (W=4000 and 5400 Da) were studied potentiometrically in aqueous solution at 25 degrees C. Measurements were made in different salt solutions: LiCl 0.1-1.5, NaCl 0.1-2, KCl 0.1-2, Et(4)NI 0.1-0.75 mol l(-1), and in artificial seawater in the salinity range 10</=S</=45. Protonation data were analysed by two different models and the dependence of the relative parameters on ionic strength were calculated. Measurements performed in interacting media (alkali metal chlorides and artificial seawater) were interpreted in terms of complex formation, and the relative formation parameters are reported. Previous data on the interaction of a higher molecular weight (W=230 000 Da) polymethacrylic acid with alkaline metal cations and Ca(2+) were reanalysed in the light of correct procedure which takes the effective polyanion charge into account. The speciation of methacrylates, in aqueous solutions containing the major constituents of natural fluids, is discussed in relation to the various parameters that influence the stability of different species formed.

Interaction of Alkyltin(IV) Compounds with Ligands of Interest in the Speciation of Natural fluids: Complexes of (CH3)2Sn2+ with Carboxylates

Complex formation by (CH3)2Sn 2+ with acetate (ac), malonate (mal), 1,2,3-propanetricarboxylate (tricarballylate, tca) and 1,2,3,4-butanetetracarboxylate (btc) ligands in aqueous solution is reported. The study has been performed by potentiometry ([H + ]‐glass electrode) at T = 25 °C, and in the 0 < I < 1 mol dm 2 3 ionic strength range. In order to evaluate the salt effects on the formation constants of the complex species, and to contribute to the definition of the chemical speciation of diorganotin(IV) compounds in natural waters where carboxylic ligands are naturally present, interactions of NaCl (which is the major component of all natural fluids), with the components of the systems under investigation have also been considered. A model for the ionic strength dependence of the formation constant was used in order to calculate the values of thermodynamic constants, at infinite dilution, for all the proposed species, by considering hydrolytic species too. A relationship between the charges on the different ligands considered and the stabilities of the complex species formed is also discussed.

Binding of acrylic and sulphonic polyanions by open-chain polyammonium cations

The interactions between some acrylic and sulphonic polyanions and some protonated amines (diamines NH(2)-(CH(2))(x)-NH(2), x=2,...,10; linear tri-, tetra-, penta- and hexa-amines) were studied potentiometrically in aqueous solution, at 25 degrees C. For both types of polyanions AL(2)H(i) (L(-), monomer of polyanion, A, amine) species are formed, with i=1,...,n (n=number of amino groups in the amine). The stability of these species is strictly dependent on the polyammonium cation charge, and fairly independent of the type of amine (in diamine species maximum stability is observed for x=4, 5). Acrylic and sulphonic polyanion complexes are considerably stronger than analogous species formed by low molecular weight anions. Mean stability can be expressed as logK=2.87zeta(2/3), for polyacrylic anions and logK=2.42zeta(2/3) for polysulphonic anions (zeta=absolute value for charge product of reactants).

Experimental and robust modeling approach for lead(II) uptake by alginate gel beads: influence of the ionic strength and medium composition.

Systematic kinetic and equilibrium studies on the lead ions removal ability by Ca-alginate gel beads have been performed by varying several internal parameters, namely, number of gel beads, nature and composition of the ionic medium and pH, which allowed us to model a wastewater in order to closely reproduce the composition of a real sample. Moreover, the effects brought about the different ionic species present in the reacting medium have been evaluated. Differential Pulse Anodic Stripping Voltammetry (DP-ASV), has been systematically used to perform kinetic and equilibrium measurements over continuous time in a wide range of concentration. Kinetic and equilibrium data have been quantitatively analyzed by means of robust approach both for the non-linear regression and the subsequent residuals analysis in order to significantly improve the results in terms of precision and accuracy. Alginate gel beads have been characterized by SEM and an investigation on their swelling behavior has also been made. Removal efficiency of the calcium-alginate gel beads has been calculated and results obtained have showed a relevant dependence on ionic strength, composition of ionic media, pH of solution and number of gel beads. The number of gel beads takes part as key crucial components, i.e., the higher the number of beads the greater the amount of Pb(II) species removed from the sample, the lower the time needed to reach the maximum removal efficiency of 90%.