Preconcentration and determination of trace amounts of lead (II) as thenoyltrifluoroacetone complex with dibenzo-18-crown-6 by synergistic extraction and atomic absorption spectrometry

A new method for the preconcentration and determination of trace amounts of lead at the μg/L level in natural waters has been established based on the formation of the thenoyltrifluoroacetone (TTA) complex with dibenzo-18-crown-6 (DB18C6) by means of synergistic extraction and back-extraction combined with atomic absorption spectrometry (AAS). The effect of various factors (synergism with TTA and DB18C6, shaking time, preconcentration factor, composition of the extracted species, and foreign ions etc.) on the extraction and back-extraction of lead has been investigated in detail. The lead-TTA chelate in o-dichlorobenzene forms a stable adduct with DB18C6 as Pb(TTA)₂ DB18C6. The stability constant (β) of the adduct determined by curve fitting method was log β = 4.2. The amount of lead in natural waters such as tap water (Kanazawa University) and Kakehashi river (Komatsu City) determined by the present method was found to be 0.64 ± 0.02 μg/L and 5.10 ± 0.03 μg/L, respectively. Received: 14 July 1997 / Revised: 3 November 1997 / Accepted: 20 January 1998     

Separation and determination of trace amounts of barium as its thenoyltrifluoroacetone complex with dibenzo-18-crown-6 by means of synergistic extraction and flame photometry

Summary A new method for the separation and determination of trace amounts of barium at the ppb-ppm level in water as its thenoyltrifluoroacetone (TTA) complex with dibenzo-18-crown-6 (DB18C6) comprises synergistic extraction and back extraction combined with flame photometry. The effect of various factors (solvent, size of crown ether, reagent concentration, shaking time, preconcentration factor, foreign ions etc.) on the extraction and back extraction of barium has been investigated. The barium TTA chelate in o-dichlorobenzene forms stable adducts with DB18C6 [Ba(TTA)₂ · nDB18C6, n=12]; the stability constants (n) of the adducts determined by means of the curve fitting method are log ₁=3.77 and log ₂=7.91. The content of barium in sodium chloride and sodium nitrate of guaranteed reagent grade was found to be 9.67±0.08 g/g and 7.86±0.09 g/g, respectively.     

Complexation Studies of N,N′-ethylenedi-L-cysteine with Some Metal Ions

As part of a search for environmentally friendly metal chelating ligands, the stability constants of N, N′-ethylenedi-L-cysteine (EC) complexes with Ca(II), Cu(II), Mg(II) and Mn(II) were determined by potentiometry with a glass electrode in aqueous solutions containing 0.1 mol⋅L⁻¹ KCl at 25 °C. Final models are proposed. For the Ca(II)–EC system, the overall stability constants are log ₁₀ β _CaHL=14.53±0.03, log ₁₀ β _CaL=4.79±0.01 and log ₁₀ β _CaL2=8.38±0.04. For the M(II)–EC systems, where M=Cu(II) or Mg(II), the overall stability constants are log₁₀ β _CuHL=31.19±0.02 and log ₁₀ β _CuL=27.02±0.06 for Cu(II), and are log ₁₀ β _MgHL=14.84±0.02 and log ₁₀ β _MgL=6.164±0.008 for Mg(II). For the Mn(II)–EC system, the overall stability constant is log ₁₀ β _MnL=10.12±0.01. Metal–chelate speciations simulations showed that EC is an efficient chelating agent for Cd(II), Co(II), Cu(II), Ni(II), Pb(II) and Zn(II) for pH≥7.     

Preconcentration and determination of trace amounts of lead (II) as thenoyltrifluoroacetone complex with dibenzo-18-crown-6 by synergistic extraction and atomic absorption spectrometry

A new method for the preconcentration and determination of trace amounts of lead at the μg/L level in natural waters has been established based on the formation of the thenoyltrifluoroacetone (TTA) complex with dibenzo-18-crown-6 (DB18C6) by means of synergistic extraction and back-extraction combined with atomic absorption spectrometry (AAS). The effect of various factors (synergism with TTA and DB18C6, shaking time, preconcentration factor, composition of the extracted species, and foreign ions etc.) on the extraction and back-extraction of lead has been investigated in detail. The lead-TTA chelate in o-dichlorobenzene forms a stable adduct with DB18C6 as Pb(TTA)₂ DB18C6. The stability constant (β) of the adduct determined by curve fitting method was log β = 4.2. The amount of lead in natural waters such as tap water (Kanazawa University) and Kakehashi river (Komatsu City) determined by the present method was found to be 0.64 ± 0.02 μg/L and 5.10 ± 0.03 μg/L, respectively.     

Complexation of M–(buffer) x –(OH) y Systems Involving Divalent Ions (Cobalt or Nickel) and Zwitterionic Biological Buffers (AMPSO, DIPSO, TAPS and TAPSO) in Aqueous Solution

The complexation behavior of eight M–(buffer) _x –(OH) _y systems involving two divalent ions (cobalt and nickel) and four zwitterionic biological buffers (AMPSO, DIPSO, TAPS and TAPSO) were characterized. Complex formation was detected for all eight M–(buffer) _x –(OH) _y systems studied, but fully defined final models were obtained for only four of these systems. For systems involving cobalt or nickel with AMPSO or TAPS, a complete characterization of the systems was not possible in the studied buffer pH-range. Metal complexation was studied by glass-electrode potentiometry (GEP) and UV-Vis spectroscopy at 25.0 °C and I=0.1 mol⋅dm⁻³ KNO₃ ionic strength. For the Ni–(L) _x –(OH) _y and Co–(L) _x –(OH) _y systems, with L = TAPSO or DIPSO, the proposed final models and overall stability constants were obtained by combining results from both techniques. For the Ni–(L) _x –(OH) _y systems, the measured values of the stability constants are log ₁₀ β _NiL=3.0±0.1 and log ₁₀ β _NiL2=4.8±0.1 for L = TAPSO, and log ₁₀ β _NiL=2.7±0.1 and log ₁₀ β _NiL2=4.6±0.1 for L = DIPSO. For the Co–(L) _x –(OH) _y systems, the overall stability constants are log ₁₀ β _CoL=2.2±0.1, log ₁₀ β _CoL2=3.6±0.2 and log ₁₀ β _CoL(OH)=7.6±0.1 for L = TAPSO, and log ₁₀ β _CoL=2.0±0.1 and log ₁₀ β _CoL(OH)=7.8±0.1 for L = DIPSO. For both buffers, the CoL(OH) species is characterized by a major structural rearrangement.     

A Combined Experimental and Theoretical Study on the Complexation of Ag<Superscript>+</Superscript> with a Hexaarylbenzene-Based Receptor

From extraction experiments and γ-activity measurements, the exchange extraction constant corresponding to the equilibrium Ag⁺(aq) + 1⋅Cs⁺(nb) ⇆ 1⋅Ag⁺(nb) + Cs⁺(aq) taking part in the two-phase water–nitrobenzene system (where 1 = hexaarylbenzene-based receptor; aq = aqueous phase, nb = nitrobenzene phase) was evaluated to be log ₁₀ K _ex(Ag⁺, 1⋅Cs⁺) = −1.0±0.1. Further, the stability constant of the hexaarylbenzene-based receptor⋅Ag⁺ complex (abbreviation 1⋅Ag⁺) in nitrobenzene saturated with water, was calculated at a temperature of 25 °C: log ₁₀ β _nb(1⋅Ag⁺) = 5.5±0.2. By using quantum mechanical DFT calculations, the most probable structure of the 1⋅Ag⁺ complex species was solved. In this complex having C₃ symmetry, the cation Ag⁺ synergistically interacts with the polar ethereal oxygen fence and with the central hydrophobic benzene ring via cation–π interaction.     

Sequestering Ability of Dicarboxylic Ligands Towards Dioxouranium(VI) in NaCl and KNO<Subscript>3</Subscript> Aqueous Solutions at <Emphasis Type="Italic">T</Emphasis>=298.15 K

The formation constants of dioxouranium(VI)-2,2′-oxydiacetic acid (diglycolic acid, ODA) and 3,6,9-trioxaundecanedioic acid (diethylenetrioxydiacetic acid, TODA) complexes were determined in NaCl (0.1≤I≤1.0 mol⋅L⁻¹) and KNO₃ (I=0.1 mol⋅L⁻¹) aqueous solutions at T=298.15 K by ISE-[H⁺] glass electrode potentiometry and visible spectrophotometry. Quite different speciation models were obtained for the systems investigated, namely: ML⁰, MLOH⁻, ML₂²⁻, M₂L₂(OH)⁻, and M₂L₂(OH)₂²⁻, for the dioxouranium(VI)–ODA system, and ML⁰, MLH⁺, and MLOH⁻ for the dioxouranium(VI)–TODA system (M=UO₂²⁺ and L = ODA or TODA), respectively. The dependence on ionic strength of the protonation constants of ODA and TODA and of both metal-ligand complexes was investigated using the SIT (Specific Ion Interaction Theory) approach. Formation constants at infinite dilution are [for the generic equilibrium pUO₂²⁺+q(L²⁻)+rH⁺ ⇌(UO₂²⁺) _p (L) _q H _r ^(2p−2q+r);β _pqr ]: log ₁₀ β ₁₁₀=6.146, log ₁₀ β ₁₁₋₁=0.196, log ₁₀ β ₁₂₀=8.360, log ₁₀ β ₂₂₋₁=8.966, log ₁₀ β ₂₂₋₂=3.529, for the dioxouranium(VI)–ODA system and log β ₁₁₀=3.636, log ₁₀ β ₁₁₁=6.650, log ₁₀ β ₁₁₋₁=−1.242 for dioxouranium(VI)–TODA system. The influence of etheric oxygen(s) on the interaction towards the metal ion was discussed, and this effect was quantified by means of a sigmoid Boltzman type equation that allows definition of a quantitative parameter (pL ₅₀) that expresses the sequestering capacity of ODA and TODA towards UO₂²⁺; a comparison with other dicarboxylates was made. A visible absorption spectrum for each complex reaching a significant percentage of formation in solution (KNO₃ medium) has been calculated to better characterize the compounds found by pH-metric refinement.     

A Spectrophotometric Study on Uranyl Nitrate Complexation to 150 °C

The formation constant of the mononitratouranyl complex was studied spectrophotometrically at temperatures of 25, 40, 55, 70, 100 and 150 °C (298, 313, 328, 343, 373 and 423 K). The uranyl ion concentration was fixed at approximately 0.008 mol⋅kg⁻¹ and the ligand concentration was varied from 0.05 to 3.14 mol⋅kg⁻¹. The uranyl nitrate complex, UO₂NO₃⁺, is weak at 298 K but its equilibrium constant (at zero ionic strength) increases with temperature from log ₁₀ β ₁=−0.19±0.02 (298 K) to 0.78±0.04 (423 K).     

Synergism of crown ethers in the thenoyl trifluoroacetone extraction of americium(III) in benzene medium

The synergism of the crown ethers (CE) dicyclohexano-18-crown-6 (DC18C6), dibenzo-18-crown-6 (DB18C6) and 18-crown-6 (18C6) has been investigated in the thenoyl trifluoroacetone (HTTA) extraction of americium(III) in benzene medium from an aqueous phase of ionic strength 0.5 and pH 3.50 at room temperature (23°C). The extracted synergistic species have the general formula Am(TTA)₃ · CE except for DC18C6 in which case the species Am(TTA)₃·2CE was also observed at high CE concentrations. The order of synergism was found to be DC18C6>DB18C6>18C6, which is the order of the basicity of CE as indicated by their ability to extract hydrogen ions from nitric acid solutions.     

Synergistic behaviour of crown ethers in the thenoyltrifluoroacetone extraction of technetium

The synergism of the crown ethers /CE/ dibenzene-18-crown-6 /DB18C6/ and 18-crown-6 /18C6/ has been investigated in the thenoyltrifluoroacetone /HTTA/ extraction of technetium from aqueous phase containing NaBH₄ into benzene at room temperature. The extracted synergistic species have the general formula TcO/OH/.TTA.CE. The order of synergism was found to be 18C6>DB18C6.     

Formation and Stability of Cadmium(II)/Phytate Complexes by Different Electrochemical Techniques. Critical Analysis of Results

In the present work the stability constants of various cadmium(II)/phytate (Phy) species were determined at T=298.15 K in NaNO₃(aq) at I=0.1 mol⋅L⁻¹ by DP-ASV (Differential Pulse Anodic Stripping Voltammetry) and by potentiometric titrations using an ISE-Cd²⁺. Cyclic voltammograms were also recorded to check the electrochemical behavior of cadmium in the presence of phytate. The results were analyzed together with previous data determined by ISE-H⁺ measurements. Data obtained were used to provide an exhaustive speciation scheme for the phytate/cadmium(II) system at different conditions, as well as a comprehensive representation of the binding ability of phytate toward cadmium(II). Different pL₅₀ values {a previously proposed empirical parameter, expressed as −log ₁₀ C _Phy, where C _Phy is the total phytate concentration necessary to bind 50% cadmium(II)} were also calculated by modeling its dependence on pH.     

Sorption of Lead(II) on Two Chelating Resins: From the Exchange Coefficient to the Intrinsic Complexation Constant

The sorption of inorganic lead(II) on two cationic resins containing different complexing groups, the iminodiacetic Chelex 100 and the carboxylic Amberlite CG-50, was investigated. The Gibbs-Donnan model was used to describe and predict the sorption through the determination of the intrinsic complexation constants. These quantities, even though non-thermodynamic, characterize the sorption as being independent of experimental conditions. The sorption mechanism for metals on complexing resins was also studied by adding a competitive soluble ligand that shifts the sorption curves to higher pH. The ligand competes with the resin for complexation with the metal ion. Lead(II) is strongly sorbed on Chelex 100 through the formation of two complexes in the resin phase: MHL with log ₁₀ β _111i =−0.3 and ML with log ₁₀ β _111i =−3.7. The presence of the competitive ligand in solution allows for the determination of a third complex. Furthermore, on Amberlite CG-50 the sorption is rather strong and involves the formation of the complex ML, in more acidic solution, with log ₁₀ β _110i =−2.0. In the presence of the ligand PyDA, the ML(OH) complex was characterized by log ₁₀ β _11−1i =−5.6. In all the experiments the hydrolysis reactions in the aqueous phase are considered quantitatively.     

Modeling of Protonation Constants of Linear Aliphatic Dicarboxylates Containing -S-Groups in Aqueous Chloride Salt Solutions,at Different Ionic Strengths,Using the SIT and Pitzer Equations and Empirical Relationships

The protonation constants of ethylenedithiodiacetic, dithiodipropionic and dithiodibutyric acids were obtained from potentiometric measurements in NaCl(aq) (I≤5 mol⋅L⁻¹) and (CH₃)₄NCl(aq) (I≤3 mol⋅L⁻¹) at t=25 °C. Their dependences on ionic strength were modeled by the SIT and Pitzer approaches. The activity coefficients of the neutral species were obtained by solubility measurements. The literature values of the protonation constants of (HOOC)-(CH₂) _n -S-(CH₂) _n -(COOH) (n=1 to 3) and (HOOC)-(CH₂)-S-(CH₂) _n -S-(CH₂)-(COOH) (n=0 to 5) in NaCl(aq) and KCl(aq) (I≤3 mol⋅L⁻¹) at 18 °C were also analyzed using the above approaches. Both the log ₁₀ K _i ^H and interaction parameter values follow simple linear trends as a function of certain structural characteristics of the ligands. Examples of modeling these trends are reported. Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users.     

The Hydrolysis of AuCl<Stack><Subscript>4</Subscript><Superscript>−</Superscript></Stack> and the Stability of Aquachlorohydroxocomplexes of Gold(III) in Aqueous Solution

The equilibria AuCl₄⁻+jOH⁻+kH₂O⇌AuCl_4−j−k (OH) _j (H₂O) _k ^k−1+(j+k)Cl⁻, β _jk (0≤j,k≤4) have been studied spectrophotometrically at 20 °C in aqueous solution. For I=2 mol⋅dm⁻³(HClO₄) the conventional constants, β _i ^*, of the equilibria, Au^*+iCl⁻ ⇌AuCl _i ^*, are equal to log ₁₀ β ₁^*=(6.98±0.08); log ₁₀ β ₂^*=(13.42±0.05); log ₁₀ β ₃^*=(19.19±0.09); and log ₁₀ β ₄^*=(24.49±0.07), where [AuCl _i ^*]=∑[AuCl _i (OH) _j (H₂O)_4−i−j ] at i=const. The hydrolysis and other transformations of AuCl₄⁻ in aqueous solution are discussed. On the basis of new and known data, a full set of equilibrium constants, β _jk , or their estimates has been obtained.     

Solvent Effect on Protonation Constants of 5, 10, 15, 20-Tetrakis(4-sulfonatophenyl)porphyrin in Different Aqueous Solutions of Methanol and Ethanol

The protonation constants of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin, H₂tpps⁴⁻, were determined in water–ethanol and water–methanol mixed solvents, using a combination of spectrophotometric and potentiometric methods at 20 °C and 0.1 mol⋅dm⁻³ sodium perchlorate as supporting electrolyte. Two protonation constants, K ₁ and K ₂, were characterized and were analyzed in various media in terms of the Kamlet, Abboud and Taft (KAT) parameters. Single-parameter correlations of the protonation constant K ₁ versus α (hydrogen-bond donor acidity) and π ^* (dipolarity/polarizability) are poor in all solutions, but dual-parameter (α and π ^*) correlation represents a significant improvement with regard to the single- and multi-parameter models. However, the single-parameter correlation of log ₁₀ K ₂ in terms of β (hydrogen-bond acceptor basicity) shows a better result than dual- and multi-parameter correlations. Linear correlation is observed when the experimental log ₁₀ K ₁ and log ₁₀ K ₂ values are plotted versus the calculated ones when the KAT parameters are considered. To evaluate the protonation constants of H₂tpps⁴⁻, the Yasuda-Shedlovsky extrapolation is used to obtain the log ₁₀ K ₁ and log ₁₀ K ₂ values at zero percent organic solvent. Finally, the results are discussed in terms of the effect of the solvent on protonation.     

D<Subscript>2</Subscript>O Isotope Effects on the Ionization of <Emphasis Type="Italic">β</Emphasis>-Naphthol and Boric Acid at Temperatures from 225 to 300 °C using UV-Visible Spectroscopy

The deuterium-isotope effects on the ionization constants of β-naphthol (2-naphthol) and boric acid, Δlog ₁₀ K=[log ₁₀ K _D2O−log ₁₀ K _H2O], have been determined from measurements in light and heavy water at temperatures from 225 °C≤t≤300 °C and pressures near steam saturation. β-Naphthol is a thermally-stable colorimetric pH indicator, whose ionization constant lies close to that of H₂PO₄⁻ (aq), the only acid for which Δlog ₁₀ K is accurately known at elevated temperatures. A newly designed platinum flow cell was used to measure UV-visible spectra of β-naphthol in acid, base, and buffer solutions of H₂PO₄⁻/HPO₄²⁻ and D₂PO₄⁻/DPO₄²⁻, from which the degree of ionization at known values of pH and pD was determined. Values of the ionization constants of β-naphthol in light and heavy water were calculated from these results, and used to derive a model for and over the experimental temperature range with an estimated precision of ±0.02 in log ₁₀ K. The new values of K _H2O and K _D2O allowed us to use β-naphthol as a colorimetric indicator, to measure the equilibrium pH and pD of the buffer solutions B(OH)₃/B(OH)₄⁻ and B(OD)₃/B(OD)₄⁻ up to 300 °C, from which the ionization constants of boric acid were calculated. The magnitude of the deuterium isotope effect for H₂PO₄⁻ (aq) is known to fall from Δlog ₁₀ K=−0.62 to Δlog ₁₀ K=−0.47, on the “aquamolal” concentration scale, as the temperature rises above 125 °C, but then remains almost constant. Although the temperature range is more limited, the new results for β-naphthol and boric acid appear to show a similar trend.     

Competitive sorption of Cu(II) and Eu(III) ions on olive-cake carbon in aqueous solutions—a potentiometric study

The competitive sorption of Cu(II) and Eu(III) ions from aqueous solutions by olive-cake carbon, has been investigated by potentiometry at pH 6, I=0.1 M NaClO₄, 25°C and under normal atmospheric conditions. Evaluation of the experimental data supports the formation of inner-sphere surface complexes and results in the calculation of the formation constant of the surface complexes ((=S–O)₂Cu), which is found to amount log β _Cu=5.3±0.3. Addition of competing Eu(III) ions in the aqueous system leads to replacement of the Cu(II) by the competitor metal ion. Evaluation of the potentiometric data obtained from competition experiments indicates an ion-exchange mechanism. The formation constant of the Eu(III) species sorbed on olive cake carbon is found to be log β _Eu=5.1±0.5. Comparison of the complex formation constants of the olive-cake carbon with the corresponding complex formation constants for of olive cake and humic acid with the two metal ions, indicates that the same type of active sites is responsible for the metal ion complexation on the surface of the different types natural organic matter (e.g. olive-cake carbon, olive-cake and humic acid).     

Equilibrium Study of the Mixed Complexes of Copper(II) with Adenine and Amino Acids in Aqueous Solution

Solution equilibria of the systems Cu(II)-adenine (A)-amino acids (L) have been studied pH-metrically. The formation constants of the resulting mixed ligand complexes have been calculated at 25 °C and ionic strength 0.1 mol⋅dm⁻³ NaNO₃. Ternary complexes are formed by simultaneous reactions. The relative stability of each ternary complex was compared with that of the corresponding binary complexes in terms of Δlog ₁₀ K values. The concentration distribution of the complexes in solution was evaluated.     

Sorption of Cu(II) and Eu(III) ions from aqueous solution by olive cake

The sorption of Cu(II) on olive cake, a biomass by-product of olive oil production, has been investigated by potentiometry at pH 6, I=0.1 M NaClO₄, 25 °C and under atmospheric conditions. Numerical analysis of the experimental data supports the formation of surface complexes and allows the evaluation of the corresponding formation constant, which is found to amount log β=5.1±0.4. This value is close to corresponding values given in literature for Cu(II)-humate complexes, indicating that the same type of active sites (e.g. carboxylic and phenolic groups) is responsible for the Cu(II) binding by olive cake. Addition of a competing metal ion (e.g. Eu(III) ion) in the system leads to replacement of the Cu(II) by Eu(III). Evaluation of the potentiometric data obtained from competition experiments indicates on a ionexchange mechanism. The formation constant of the Eu(III) species sorbed on olive cake is found to be log β=5.4±0.9. The results of this study are of particular interest with respect to waste water treatment technologies using biomass products as adsorbent material and environmental impact assessments regarding disposal of biomass by products in the geosphere.     

The Examination of the Activity Coefficients of Cu(II) Complexes with OH<Superscript>−</Superscript> and Cl<Superscript>−</Superscript> in NaClO<Subscript>4</Subscript> Using Pitzer Equations: Application to Other Divalent Cations

The stability constants for the hydrolysis of Cu(II) and formation of chloride complexes in NaClO₄ solution, at 25 °C, have been examined using the Pitzer equations. The calculated activity coefficients of CuOH⁺, Cu(OH)₂, Cu₂(OH)³⁺, Cu₂(OH)₂²⁺, CuCl⁺ and CuCl₂ have been used to determine the Pitzer parameter (β _i ⁽⁰⁾, β _i ⁽¹⁾, and C _i ) for these complexes. These parameters yield values for the hydrolysis constants (log ₁₀ β ₁^*, log ₁₀ β ₂^*, log ₁₀ β _2,1^* and log ₁₀ β _2,2^*) and the formation of the chloride complexes (log ₁₀ β _CuCl^* and that agree with the experimental measurements, respectively to ±0.01,±0.02,±0.03,±0.06,±0.03 and ±0.07. The stability constants for the hydrolysis and chloride complexes of Cu(II) were found to be related to those of other divalent metals over a wide range of ionic strength. This has allowed us to use the calculated Pitzer parameters for copper complexes to model the stability constants and activity coefficients of hydroxide and chloride complexes of other divalent metals. The applicability of the Pitzer Cu(II) model to the ionic strength dependence of hydrolysis of zinc and cadmium is presented. The resulting thermodynamic hydroxide and chloride constants for zinc are and . For cadmium the thermodynamic hydrolysis constants are and . The Cu(II) model allows one to determine the stability of other divalent metal complexes over a wide range of concentration when little experimental data are available. More reliable stepwise stability constants for divalent metals are needed to test the linearity found for the chloro complexes.