Effects of the detection window on the determination of organic copper speciation in estuarine waters

The complexation of copper by natural organic ligands in sea water was measured by cathodic stripping voltammetry with ligand (catechol and quinolin-8-ol) competition. Two methods to determine copper complexation in estuarine waters were compared, one based on a complete titration of the complexing capacity of the sample and the other on measurement of the labile and total dissolved metal concentrations only. Values for log α_CuL (ihe α-coefficient for complexation of Cu²⁺ by natural organic ligands) ranging from 3.2 to 7.7 and from 3.3 to 7.8 could be detected by varying long α_CuAL (the α-coefficient for complexation of Cu²⁺ by the added competing ligand) from 3.4 to 8.9 in samples from the Tamar estuary and from the Channel. The two methods gave comparable results and showed that the type of sites detected depends on the detection window of the technique. This effect is due to the sea and estuarine water samples containing a series of complexing ligands forming complexes of greatly varying strength, thus causing a rnage of complex stabilities to be measured as a function of the detection window of each technique. A comparison showed that lower values for α_CuL are obtained by anodic stripping voltammetry as a result of that technique having a lower detection window. A detailed study of the Tamar estuary revealed a decrease in log α_CuL from 10.8 to 8.3 with increasing salinity, demonstrating that major cations compete with copper for the complexing sites. The free Cu²⁺ concentrations were very low throughout the estuary (16.2 < pCu²⁺ < 18.2) even though the total measurements to establish potential toxic effects of copper in natural waters.     

The use of Nafion-coated thin mercury film electrodes for the determination of the dissolved copper speciation in estuarine water

Differential pulse anodic stripping voltammetry (DPASV) using a Nafion-coated thin mercury film electrode (NCTMFE) was implemented to determine the dissolved copper speciation in saline estuarine waters containing high concentrations of dissolved organic matter (DOM). The study used model ligands and estuarine water from San Francisco Bay, California, USA to demonstrate that the NCTMFE is more effective at distinguishing between electrochemically inert and labile copper species when compared to the conventional thin mercury film electrode (TMFE). Copper titration results verify that the NCTMFE better deals with high concentrations of DOM by creating a size-exclusion barrier that prevents DOM from interacting with the mercury electrode when performing copper speciation measurements. Pseudovoltammograms were used to illustrate that copper complexes found in natural waters were more apt to be electrochemically inert at the NCTMFE relative to the TMFE when subjected to high negative overpotentials. Copper speciation results using the NCTMFE from samples collected in San Francisco Bay estimated that >99.9% of all copper was bound to strong copper-binding ligands. These L₁-class ligands exceeded the concentration of total dissolved copper in all samples tested and control the equilibrium of ambient [Cu²⁺] in the San Francisco Bay estuary.     

Electrochemical speciation of dissolved Cu, Pb and Zn in an estuarine ecosystem (Ria de Vigo, NW Spain): comparison between data treatment methods

The total concentration and chemical speciation of Cu, Pb and Zn were determined by square wave anodic stripping voltammetry (SWASV) in the Ría de Vigo, an estuarine area located in NW Spain. Surface and bottom waters from 6 locations were collected in two seasons during 3 years. The total Pb was below 1 nM, and Cu and Zn concentrations, ranged from 3 to 44 nM and from 9 to 300 nM respectively. A gradient from sampling points located in the port of Vigo to external areas was observed. The speciation of the metals (ligand concentration and apparent complex formation constant K′) was calculated using several methods: The Langmuir and Scatchard linear fits for one and two ligands, the Lorenzo non-linear fit for one ligand and Langmuir non-linear fit for two ligands. The capability of the different methods to achieve reliable results have been discussed and Langmuir linear fit as well as Lorenzo non-linear fit are the most suitable. Cu presented the highest ligand concentrations, followed by Zn and Pb, while mean log K′ values fell in the range 5-9 (±0.6) for all metals and samples. The adjustment of the data treatment methods used to calculate the speciation parameters was found to vary depending on the extent of complexation and on whether one or two ligands needed to be considered.     

Trace metal speciation measurements in waters by the liquid binding phase DGT device

The speciation measurements of trace metals by the diffusive gradients in thin-films technique (DGT) using a poly(4-styrenesulfonate) (PSS) aqueous solution as a binding phase and a cellulose dialysis membrane (CDM) as a diffusive layer, CDM-PSS DGT, were investigated and showed good agreement with computer modelling calculations. The diffusion coefficients of ethylenediaminetetraacetic acid (EDTA) complexes with Cd²⁺ and Cu²⁺ were measured and compared with those of the inorganic metal ions. CDM-PSS DGT device was tested for speciation measurement in sample solutions containing EDTA, tannic acid (TA), glucose (GL), dodecylbenzenesulfonic acid (DBS) and humic acid (HA) as complexing ligands forming organic complexes with varying stability constants. Lower percentages of DGT labile copper concentrations over total filterable copper concentrations obtained from the deployments in freshwater sites indicated that copper complexes with organic matter were basically not measured by the devices.     

Determination of complexing capacities of ligands in natural waters and conditional stability constants of the copper complexes by means of manganese dioxide

A dispersion of manganese dioxide is used as a weak ion exchanger in the determination of the complexing capacities of natural waters for copper and in the estimation of the stability constants of the complexes formed, at the concentration and pH at which the ligands occur in natural waters. Experiments were done at 25°C and 0.01 M ionic strength. Stability constants varied from 10^7.8 to 10^8.8 at pH 7.6 for ligands in lakes and rivers. The constant for the copper—fulvic acid complex was estimated as 10^7.8 at pH 7.6. Only one complexing site of major importance for natural water environments was observed.     

Copper(II) complexing with <Emphasis Type="Italic">N′,N′</Emphasis>-diethylbenzohydrazide

Copper(II) complexing with N′,N′-diethylbenzohydrazide (DEBH) in aqueous isopropanol was studied. The formation of cationic complexes with the ratio [Cu²⁺]: [DEBH] = 1: 1 and 1: 2 in week acid solution and an uncharged complex with the ratio [Cu²⁺]: [DEBH] = 1: 2 in neutral and alkaline solutions was established. Their stability constants K _st were determined. The complexes were isolated in a solid state and characterized by IR spectroscopy and elemental analysis for copper.     

Copper speciation by competing ligand exchange method using differential pulse anodic stripping voltammetry with ethylenediaminetetraacetic acid (EDTA) as competing ligand

A technique has been developed to study chemical speciation of copper in freshwaters by competing ligand exchange (CLE) method using anodic stripping voltammetry (ASV) in the differential pulse (DP) mode with ethylenediaminetetraacetic acid (EDTA) as a competing ligand. The voltammetric behavior of Cu(II)-EDTA complex has been investigated using DPASV. When DPASV is used at an appropriate deposition potential, the inert Cu(II)-EDTA complex becomes electroactive, and is reduced directly. Furthermore, at the same deposition potential, Cu(II)-fuvic acid and Cu(II)-humic acid complexes do not contribute significantly to the analytical signal, which makes EDTA a suitable competing ligand in the determination of copper speciation using CLE-ASV. This method has been applied to freshwater samples from Rideau Canal (Ottawa, ON, Canada). The analysis of the copper titration data of these freshwater samples has indicated the presence of a very strong copper-binding ligand with a conditional stability constant of approximately 10²⁰ and a corresponding very high concentration (above 100 nM) of the ligand.     

Stabilities of the Ternary Complexes of Copper(II) with Substituted 1,10-Phenanthrolines and Some Amino Acids in Aqueous Solution

In this study the binary and ternary complexes of copper(II) with substituted 1,10-phenanthrolines [s-phen: 1,10-phenanthroline (phen), 4,7-dimethyl-1,10-phenanthroline (dmphen) and 5-nitro-1,10-phenanthroline (nphen)] and l-amino acids [aa: l-phenylalanine (phe), l-tyrosine (tyr) and l-tryptophan (trp)] have been investigated using potentiometric methods in 0.1 mol·L^?1 KCl aqueous ionic media at 298.2 K. The protonation constants of the ligands and the stability constants of the binary and ternary complexes of Cu(II) with the ligands were calculated from the potentiometric data using the “BEST” software package. It was inferred that the aromatic 1,10-phenanthrolines act as a primary ligand in the ternary complexes, while the oxygen and nitrogen donor-containing amino acids are secondary ligands. The observed values of Δlog₁₀ K indicate that the ternary complexes are more stable than the binary ones, suggesting no interaction takes place between the ligands in the ternary complexes. The magnitudes of the measured stability constants of all of the ternary complexes are in the order [Cu(s-phen)(trp)]⁺ > [Cu(s-phen)(tyr)]⁺ > [Cu(s-phen)(phe)]⁺, which is identical to the sequence found for the binary complexes of Cu(II) with the amino acids. When the substituted 1,10-phenanthroline is changed, the stability constants of the ternary complexes decrease in the following order: [Cu(dmphen)(aa)]⁺ > [Cu(phen)(aa)]⁺ > [Cu(nphen)(aa)]⁺.     

Organotitanium chemistry: VII. Study on HPLC of bis- and mono-(substituted cyclopentadienyl)titanium derivatives

The high-performance liquid chromatographic behavior of 56 bis- and mono-(substituted cyclopentadienyl)titanium dichlorides was investigated. According to their capacity factors (K′) and separation efficiencies (N), the relationship between chromatographic behavior and structure of titanium complexes was discussed.     

Binuclear schiff-base complexes of copper(II) linked by phthaloyl as a bridging group

Binuclear Schiff-base complexes were prepared by bridging an unsymmetrical tetradentate Schiff-base complex of copper(II) with m- or p-phthaloyl. The complexes were characterized by means of elemental analyses, molecular weights, UV, IR and ¹H NMR (for metal-free ligands) spectra. ESR and magnetic susceptibility measurements show that the copper(II)copper(II) interaction is negligibly small.     

Voltammetric measurement of copper(II)/organic interactions in estuarine waters

The voltammetry of copper in organic ligand/chloride media is dominated by the formation of CuCl^?₂ species and by induced adsorption of Cu(I) in organic coatings on the electrodes. These phenomena are utilised in a novel method for evaluating Cu(II)/organic ligand interactions, based on the principle of ligand exchange. The Cu(II)/organic species competes with glycine which forms copper glycinate. These two complexes can be distinguished voltammetrically: copper glycinate gives a higher surface excess of copper at a gelatin-coated hanging mercury drop electrode, partly because of the increased production of CuCl^?₂ from copper glycinate at the electrode surface. The method proved satisfactory for pure ligand/surfactant/chloride media and for estuarine waters. It is shown that there are two type of Cu(II)-binding ligand in estuarine waters: humic material (> 10^?6 mol l^?1, assuming 1:1 site binding) with polyelectrolyte-type binding, and discrete ligands (? 10^?6 M) with stability constants around 10⁹. The extent of Cu(II) binding by the humic material decreases down the estuary because of dilution and increased salinity.     

Thermodynamics of the complexing of uranyl ions with 1-phenyl-3-methyl-4-benzoylpyrazolone-5 in aqueous dioxane

The thermodynamics of the complexing between hexavalent U and 1-phenyl-3-methyl-4-benzoylpyrazolone-5 (PMBP) have been studied in 70 vol% aqueous—dioxane medium at 25 and 35±0.1°C following the Bjerrum—Calvin pH titration technique, as applied by Van Uitert and Haas. The ligand is mono-protonic. The refinement of results of formation constants has been accomplished by the method of least squares treatment after an algebraic transformation. The formation of 1:1, 1:2 and 1:3 complexes has been observed, the order of stability being log K₁ > log K₂ > log K₃. The stability invariably increases with an increase in temperature both in aqueous as well as aqueous dioxane media. The changes in ΔG⁰, ΔH⁰ and ΔS⁰ at 25 and 35°C for the overall equilibrium constants have also been evaluated. Uranyl complexes of PMBP are entropy stabilized, the values of enthalpy changes being positive. Other factors which affect chelate stability are briefly discussed.     

NMR studies of dynamic behavior of dialkyl(acetylacetonato)bis(tertiary phosphine)cobalt(III) and related complexes in solution

The ¹H, ³¹P and ¹³C NMR spectra of cis-dialkyl(acetylacetonato)bis(tertiary phosphine)cobalt(III) complexes were obtained in several solvents. These complexes have an octahedral configuration with trans tertiary phosphine ligands. The coordinated tertiary phosphine ligands are partly dissociated in solution. One of the phosphine ligands in CoR₂(acac)(PR₃′)₂ can be readily displaced with pyridine bases to give pyridine-coordinated complexes. From observation of the ¹H and ³¹P NMR spectra several kinetic and thermodynamic data for exchange reactions and displacement reactions of tertiary phosphines were obtained.     

Synthesis and properties of alkylruthenium complexes bearing primary and secondary amine ligands

A series of 18-electron alkylruthenium complexes, RuR[κ²(N,N′)-(S,S)-R′SO₂NCHPhCHPhNH₂](η⁶-arene) (Ph = C₆H₅, R′ = p-CH₃C₆H₄ and CH₃), bearing a N-sulfonylated diamine ligand was synthesized from the reaction of RuCl[κ²(N, N′)-(S,S)-R′SO₂NCHPhCHPhNH₂](η⁶-arene) with alkylzinc reagents, in which transmetalation proceeded smoothly to give the desired alkyl complexes in good yield and selectivity. Although the isolable amine Ru complexes bearing functionalized alkyl ligands were thermally stable, the simple methyl and ethyl Ru complexes underwent intramolecular deprotonation from NH protons to give the amido Ru complexes with release of the alkanes. The reactivity of the alkyl Ru complexes is highly affected by the structures of the arene ligands.     

The stabilities and formation kinetics of some macrocycles with copper(II): crystal structures of some pendant arm macrocycles

Kinetics of complex formation and stability constants of tetra-(2-hydroxpropyl) substituted cyclam (L³) and cyclen (L⁴) with copper(II) have been studied in aqueous solution at room temperature. These data are compared to the corresponding parent compounds (cyclam L¹ and cyclen L²) in an attempt to define the effect of pendant arm upon kinetics and stability constants of the complexes. The kinetics were observed by stopped-flow measurements followed at multiwavelengths. These ligands were chosen to furnish information concerning effect of pendant groups and cavity size on the kinetics and stability of the complexes. Stopped-flow and spectrophotometric titration techniques were used for evaluation of the kinetics and stability constants, respectively. The apparent rate constants increase as CuL³?>?CuL⁴?>?CuL¹?>?CuL². Activation parameters and stability constants of the complexes were estimated. The effect of cavity size on the rate of reaction can be observed in CuL³?>?CuL⁴ and CuL¹?>?CuL² and the effect of pendant groups in CuL³?>?CuL¹ and CuL⁴?>?CuL². Mechanism of the complex formation reaction is proposed. The enhanced stability of the copper(II) complexes formed with L¹ and L² macrocyclic ligands is compared to those formed with analogous pendant arm species.     

The effect of ligand donor atoms on ternary complex stability

Formation constants of mixed ligand complexes of Cu²⁺, Zn²⁺, Ni²⁺, Co²⁺, and Mn²⁺,with cyadine-5′-monophosphoric acid (CMP) and various primary ligands such as 1,10-phenanthroline(phen), glycylglycine(glygly) and salicylic acid (sal) have been determined in aqueous solution at 35°C and 0.1 M (KNO₃) by potentiomeric measurements. The acid dissociation constants of all the above mentioned ligands together with their 1 : 1 binary metal complex formation constants were also measured at 35°C. In general all the 1 : 1 binary complexes follow the Irving-Williams order of stability. Further the binary metal complexes of primary ligands are more stable than their ternary complexes with CMP. For ternary complexes, Δ(log K) values seem to change from positive to highly negative as the coordinating atoms of the primary ligands were varied from N,N to N,O^? to O^?O^?. The higher stability of ternary complexes involving phen is due to its Π-bonding interaction with the above metal ions and the relative decrease in the stability of other ternary systems is due to the coulombic repulsion of donor oxygen atoms of primary and secondary ligands. Thus for ternary complexes the stabilities follow a decreasing order of M-phen-CMP > M-glygly-CMP > M-sal-CMP.     

Increased Sensitivity Spectrophotometric Flow Analysis Method for Copper Determination in Water Samples

A reverse configured flow injection system was developed for the determination of copper in water samples. In this study, a bathocuproine disulfonic acid copper complexing reagent was used. In the presence of a reducing agent (hydroxylamine), the formation of complex was monitored at 484 nm. The determination range extended from 1 to 40 µg L^?1, with an applicable determination rate of 40 h^?1. The developed method was applied to the determination of copper in water samples (estuarine, river, and drinking water) and showed good accuracy (z-score below 2). The detection limit of 0.7 µg L^?1 copper is consistent with the requirement of the target water samples. The developed method was also used for the comparison of different spectrophotometric flow cells. Alternative flow cells (U, Z shaped, and the liquid waveguide capillary cell) were compared in terms of their sensitivity and response to refractive index changes.     

A novel adsorbent for the determination of the toxic fraction of copper in natural waters

A novel adsorbent for the determination of the toxic fraction of copper in natural waters is described. Aluminium hydroxide adsorbed on a sulfonic acid cation-exchange resin quantitatively retains copper(II) ions in the absence of organic ligands such as fulvic, humic and tannic acids. In the presence of these ligands, a smaller fraction of copper is adsorbed and can be related to the toxic fraction. The toxic fraction determined by this method agreed well with results of algal assay with the marine diatom Nitzschia closterium in seawater and the green alga Chlorella pyrenoidosa in a synthetic soft water. The aluminium hydroxide-coated column also quantitatively adsorbs lipid-soluble copper complexes, which can be leached selectively from the column with methanol. The Al:OH ratio on the resin was 1:2 and the conditional stability constants (log K) of the Cu²⁺-adsorbent complexes in seawater and synthetic soft water were found to be 9.87 and 11.10, respectively; these values are similar to the equilibrium constatns for the reaction between Cu²⁺ and algae. The application of this adsorbent in an in-situ instrument for the continuous, unattended determination of the toxic fraction of copper and some other toxic metals in natural waters is outlined.     

Comparative study of copper(II) interactions with monomeric ligands and synthetic or natural organic materials from potentiometric data

Potentiometric measurements were used to characterize the complexing properties of (a) a mixture of five monomeric ligands, (b) a synthetic humic-like substance and (c) fulvic acids extracted from soils, with copper (II). In order to compare the binding strengths involved, the same mathematical treatments of the data were used for all measurements. Calculations of the total ligand concentration with the Gran function give underestimated values for the multiligand mixture because of the known presence in the mixture of functional groups with pK^H ; 11 which > cannot be titrated and are revealed only by complexation phenomena. The acid-base properties of the humic substances are better described with a continuous model than with the descrete Henderson-Hasselbach model, because of the inability to distinguish properly between equivalent and independent types of functional groups. In the presence of copper (II), the formation functions show that a mixture of different kinds of complexes with different stability constants is probably formed. Extra protons released during the titration of the various copper (II) systems with alkali are attributed to untitrated functional groups with extremely low protonation constants in the case of the multiligand mixture, but ambiguity remains with the humic substances because their chemical structure is not known. Comparison of binding strengths can be made in terms of global conditional stability constants, by taking into account the three parameters, pH, concentrations of metal and of ligand. It is shown that the mechanisms of complexation are different for monomers and for polymers.     

Bifunctional Cyclam‐Based Ligands with Phosphorus Acid Pendant Moieties for Radiocopper Separation: Thermodynamic and Kinetic Studies

Two macrocyclic ligands based on cyclam with trans‐disposed N‐methyl and N‐(4‐aminobenzyl) substituents as well as two methylphosphinic (H₂ L1 ) or methylphosphonic (H₄ L2 ) acid pendant arms were synthesised and investigated in solution. The ligands form stable complexes with transition metal ions. Both ligands show high thermodynamic selectivity for divalent copper over nickel(II) and zinc(II)—K(CuL) is larger than K(Ni/ZnL) by about seven orders of magnitude. Complexation is significantly faster for the phosphonate ligand H₄ L2 , probably due to the stronger coordination ability of the more basic phosphonate groups, which efficiently bind the metal ion in an “out‐of‐cage” complex and thus accelerate its “in‐cage” binding. The rate of Cu^II complexation by the phosphinate ligand H₂ L1 is comparable to that of cyclam itself and its derivatives with non‐coordinating substituents. Acid‐assisted decomplexation of the copper(II) complexes is relatively fast (τ_1/2=44 and 42 s in 1 M aq. HClO₄ at 25 °C for H₂ L1 and H₄ L2 , respectively). This combination of properties is convenient for selective copper removal/purification. Thus, the title ligands were employed in the preparation of ion‐selective resins for radiocopper(II) separation. Glycidyl methacrylate copolymer beads were modified with the ligands through a diazotisation reaction. The separation ability of the modified polymers was tested with cold copper(II) and non‐carrier‐added ⁶⁴Cu in the presence of a large excess of both nickel(II) and zinc(II). The experiments exhibited high overall separation efficiency leading to 60–70 % recovery of radiocopper with high selectivity over the other metal ions, which were originally present in 900‐fold molar excess. The results showed that chelating resins with properly tuned selectivity of their complexing moieties can be employed for radiocopper separation.