Donald S. Gamble

The structure and equilibria of a manganese(II) complex of fulvic acid studied by ion exchange and nuclear magnetic resonance

The binding of Mn2+ to a well characterized fulvic acid sample is reported based on the competition with K+ in an ion exchange equilibration. The free energy of binding of to fulvic acid is only 1–2 kJ/equivalent more favourable than that for K+. This suggests an outer sphere electrostatic structure for the complex. The suggestion is confirmed by observation of minimal change in the presence of fulvic acid of the effect of paramagnetic Mn2+ on the nmr spectra of water. The interpretation of nmr spectra is supported by comparison with nmr measurements of Mn2+ complexes with simple ligands and contrast with nmr measurements on Fe3+ – fulvic acid complexing. The latter is confirmed as inner sphere.

Interaction of atrazine with Laurentian humic acid

Abstract Ultrafiltration fractionation and liquid chromatography have been applied to study the binding and hydrolysis of polar herbicide atrazine on a stoichiometrically well characterized Laurentian humic acid. The main advantage of this method over gas chromatography is the simultaneous determination of both free and bound atrazine, hydroxyatrazine and copper(II) ion with satisfactory accuracy and precision. Atrazine binding requires extensive carboxylate site protonation but the binding sites represent only a very small fraction of total carboxylate of humic acid. The results show that binding of atrazine is not competitive with binding of the hydrolysis product hydroxyatrazine, the binding capacity is reduced at higher ionic strength or by cation competition for carboxylate and the atrazine binding constant and free energy of binding can be fitted by a single value at all pH values. The differences between atrazine binding by fulvic acid and humic acid can be ascribed to the structure difference, one being a flexible linear polymer and the other a three-dimensional colloidal gel particle.

Interaction of atrazine with Laurentian fulvic acid: binding and hydrolysis.

Abstract Ultrafiltration fractionation and liquid chromatography (LC) have been applied to the study of the binding and hydrolysis of the polar herbicide atrazine on a stoichiometrically well characterized fulvic acid. Binding requires extensive carboxylate site protonation but the binding sites represent a very small fraction of total carboxylate. The data show that binding of atrazine is not competitive with binding of the hydrolytic product hydroxyatrazine. However, smaller molecular weight fractions of the fulvic acid mixture compete with atrazine for sites on the larger molecular weight fraction. Binding equilibrium is not rapid. A model of binding involving hydrogen bonding and/or charge-transfer complexing to specific sites created dynamically by the conformational equilibria of the higher molecular weight polymeric fulvic acid fractions is proposed as the best accommodation of the variety of observed facts.

Light scattering measurements of Cu(II)-fulvic acid complexing: The interdependence of apparent complexing capacity and aggregation

Abstract The Armadale Bh horizon fulvic acid is known to have intramolecular salicylic acid type bidentate chelation sites for Cu(II). The number of these sites available to Cu(II) can be exactly predicted as a function of pH. Under certain experimental conditions, aggregation and carboxylate complexing sites occur together. They are “pseudochelation” bidentate or polydentate sites, that are intermolecular but within aggregate particles. Complexometric Cu(II) titration monitored by Rayleigh light scattering gives an end point that distinguishes between the intramolecular and intermolecular types of sites. The effects of pH, aggregation and metal ion type on apparent complexing capacity are identified.

The solution phase complexing of atrazine by fulvic acid: Equilibria at 25°c

Abstract The solution phase complexing equilibria of atrazine by fulvic acid at 25°C±1.° have been investigated over the pH range of 1.3 to 6.0. Experiments with 0.1MKC1 and chelated Cu(II) are compared with those without metal ions. The use of a fulvic acid having calibrated acidic and Cu(II) chelation properties has made it possible to obtain stoicheometricly “exact”; chemical information. This is correlated with previous hydrolysis kinetics work. It is concluded that atrazine is hydrogen bonded in a labile equilibrium, to an identifiable set of protonated carboxyl groups, which act as Bronsted acid catalysts for hydrolysis. 0.1M KC1 changes (1‐αA), the degree of protonation of the carboxyl groups, without otherwise affecting the atrazine complexing. Cu(II) chelation both reduces and weakens the complexing through a combination of carboxyl group blocking, and fulvic acid aggregation. Simple equations are presented for predictive calculations.

Solution Phase Interaction of Lindane with Fulvic Acid: Effect of Solution pH and Ionic Strength

Abstract As part of an investigation of the factors influencing the interaction of different classes of pesiticides with humic substances, a study was made of the role of the following physicochemical variables on the adsorption of a typical non-polar pesticide (lindane) by a calibrated fulvic acid fraction which can exist in both colloidal solution and in precipitated form: degree of protonation; ionic atmosphere; and extent of humic matter aggregation. Using the fulvic acid as a typical humic material, and the experimental parameters of pH and ionic strength, along with ultrafiltration techniques, we were able to demonstrate the importance of these physicochemical variables on binding of lindane. From these results predictions could be made about binding mechanisms and environmental implications. The findings are likely to be applicable to all non-polar pesticides having aqueous solubility similar to that of lindane.

The Interrelationship of Aggregation and Cation Binding of Fulvic Acid

Practical problems associated with metal ions in soil solutions and surface waters have led to the investigation of two related phenomena. They are the effects of dissolved humic materials on metal ion speciation and on the metal ion complexing capacity of the water. Several years of work by Wershaw and coworkers have demonstrated that dissolved humic materials can aggregate (Wershaw et al., 1967, 1970, 1973, 1973). In addition research by Schnitzer (Schnitzer et al,, 1965; Stevenson, 1976) and earlier workers (Broadbent et al., 1952; Coleman et al., 1956; Beckwith, 1959) proved that humic materials make the most important contribution to complexing capacity. A number of authors have suggested that aggregation and cation binding are related (Stevenson, 1976; Senesi et al., 1977; Ghosh et al., 1981). A preliminary report has outlined the application of Rayleigh light scattering to the investigation of this relationship (Underdown et al., 1981). The objective of this review is to determine the extent to which stoichiometricly exact chemistry can be deduced from the available experimental evidence. The Armadale Bh horizon fulvic acid is the only humic sample available to date with which this may be done.

Determination of Trace Element Levels in Natural Fresh Water by Inductively Coupled Plasma Mass Spectrometry

Abstract Concentrations of trace elemental constituents in water draining an Eastern Ontario agriculture watershed have been determined using inductively-coupled plasma mass spectrometry. Water samples were collected in the Spring of 1991 from three locations. Unfiltered, 0.4 μm filtered as well as ultrafiltered fractions were analyzed. A total of 79 elemental isotopes ranging from 6Li to 232Th were utilized for analytical calibration to measure the concentrations of 38 trace and ultratrace inorganic elemental constituents. Estimates of concentrations were made for: Li, Be, B, Sc, V, Cr, Mn, Ni, Co, Cu, Zn, Ga, As, Br, Rb, Sr, Y, Mo, I, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Pb, Th and U. Typical levels found ranged from a mean of 0.05 μg/L for the rare earth elements to 330 μg/L for Sr. For the majority of elements, no differences in concentrations were evident between sampling locations or due to filtration. Exceptions were concentrations of Li, Mn and Pb which were affected by ...

Interactions Between Natural Organic Polymers and Metals in Soil and Freshwater Systems: Equilibria

The equilibrium metal ion-binding reactions of natural organic polymers in soils and surface waters can be understood and predicted with mathematical descriptions that are based on chemical stoichiometry. The reactivity of individual species depends on physical states and chemical composition variables. Equilibria are described by a formalism that applies the concept of weighted averages to the law of mass action and accounts for chemical composition variables with mole fraction relationships. The chemically blind “black box” empirical descriptions lack predictive abilities and are no longer necessary. The analytical chemistry and the physical chemistry of this class of systems have become indistinguishable, because of the intimate interrelationship between measurements of stoichiometry and the theoretical basis for predictive equations. Future advances depend on analytical chemical research.

The reactions of paraquat and divalent metal ions with humic acid: factors influencing stoichiometry

Abstract Laurentide humic acid has been titrated with paraquat and with selected divalent metal ions. In some cases, the humic acid was spiked with one cation before titration with another one. Several equivalence points were determined for the binding of the divalent cations, including paraquat. Three equivalence points agreed well with values predicted from the acidic properties of the humic acid. Eight independent experiments gave nine replicate values for an equivalence point that corresponds to 79.2 mole % of the total pairs of carboxyl groups. It is postulated that this represents a large molecular weight or structural fraction of the humic acid. The remaining 20.8 mole % can either bind one divalent cation to two carboxylate anions or bind one divalent cation to one carboxylate anion, with another anion providing for charge balance. Aggregation ‐ disaggregation and dissolution ‐precipitation phenomena may determine which case prevails, and they in turn are sensitive to the chemical compositions of ...