James H. Ephraim

Linköping University, Linköping, Östergötland, Sweden

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Publications (24)81.24 Total impact

  • Maria Nordén, James Ephraim, Bert Allard
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    ABSTRACT: The complexation of an aquatic fulvic acid, FA, with Sr2+ and Eu3+ was studied using an ultrafiltration technique and an ion exchange distribution method. The total amount of bound metal (Sr2+ and Eu3+) was measured as a function of pH at low metal concentrations (trace levels) and constant FA concentration. In the Sr-FA system the bound metal fraction increased slightly with pH, and the values obtained from the two experimental techniques were comparable. For Eu-FA, according to the ultrafiltration data, the fraction of bound metal ion was relatively insensitive to pH changes, whereas values from the ion exchange measurements showed a strong and positive dependence on pH. The results are discussed in the light of possible intrinsic problems of the two methods.
    10/2006: pages 297-303;
  • Environmental Science and Technology 04/2002; 23(3). DOI:10.1021/es00180a014 · 5.48 Impact Factor
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    ABSTRACT: Partial least squares (PLS) modeling was applied to investigate number-average molecular weights (Mn) and weight-average molecular weights (Mw) of fulvic acids (FAs) in relation to the corresponding UV/VIS spectra. The Mn and Mw values were determined by size exclusion chromatography (SEC). The impact of pH control, wavelength range and density as well as smoothing and derivation of spectra were tested. It was found that PLS models based on absorbance spectra can be a fast and powerful complement to existing techniques employed for determination of molecular weights of FAs. Control of pH of the FA solutions is important for the performance of the models. The models were also compared with the best univariate alternatives.
    Chemosphere 03/1999; 38(4):783-94. DOI:10.1016/S0045-6535(98)00215-X · 3.50 Impact Factor
  • Radiochimica Acta 01/1999; 84:205-211. · 1.41 Impact Factor
  • M Nordén, J H Ephraim, B Allard
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    ABSTRACT: Effects of competing ions, Fe (2+)Fe (3+) and Al(3+), on Eu(3+) complexation with an aquatic fulvic acid (FA), have been investigated using an ion exchange technique. The influence of different concentrations (10(-6), 10(-4) M) of the competing ions on the distribution coefficient for Eu was measured, and the overall complex formation function, beta(ov), was resolved for the Eu systems with Fe and Al. All systems showed pH-dependent beta(ov)-functions. The presence of 10(-4) M concentration of competing ion reduced the resolved complex formation function (logbeta(ov)) for Eu complexation with fulvic acid by 0.6 and 0.4 log units at pH 5 for Fe and Al, respectively. this indicates that Fe has a more perturbing effect on Eu-FA complexation than Al. In similar competition studies Sr and Eu were found not to perturb each others complexation with fulvic acid, suggesting therefore that the two metals probably bind to different sites on the fulvic acid molecule.
    Talanta 06/1997; 44(5):781-6. DOI:10.1016/S0039-9140(96)02102-9 · 3.51 Impact Factor
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    A S Mathuthu, J H Ephraim
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    ABSTRACT: The binding of cadmium to a fulvic acid (FA) extracted from peat was studied as a function of pH (4-8), ionic strength (0.01 and 0.10 M NaNo(3)) and ratio of fulvic acid to metal ion concentrations (FA Cd = 8, 4 , and 2). An overall complex formation function of approximately 10(3.14) was determined to enable comparison with previous studies. Additionally, literature values of complex formation constants were employed to describe the interaction between Cd(II) and the individual acidic sites. A good prediction of the experimental results is considered as a justification of the functionalities assigned to the predominant acidic sites in the fulvic acid molecule.
    Talanta 01/1996; 42(12):1803-10. DOI:10.1016/0039-9140(95)01627-9 · 3.51 Impact Factor
  • James H. Ephraim, Catharina Pettersson, Bert Allard
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    ABSTRACT: The overall acid-base properties of humic substances have been postulated to be affected by the functional group heterogeneity and heterogeneity in molecular size leading to an ionic strength effect. In this paper, the acidic properties of various molecular size fractions (500, 1000, 5000, 10 000 daltons as per ultrafiltration) of an aquatic fulvic acid (Rådsla FA) are determined and correlated to other physicochemical parameters such as UV, FTIR, and molecular weight determinations by gel-filtration chromatography. There was a positive correlation between the size cut-off as per ultrafiltration and the molecular weight determinations from the gel-filtration chromatography. The acid-base titrations of the filtrates and retentates corroborate the hypothesis that ionic strength effects are significantly larger for samples with higher molecular weight moieties.
    Environment International 01/1996; 22(5):475–483. DOI:10.1016/0160-4120(96)00039-6 · 5.66 Impact Factor
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    A S Mathuthu, J A Marinsky, J H Ephraim
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    ABSTRACT: Application of the unified physicochemical approach to the description of the dissociation properties of Laurentide fulvic acid, extracted from peat, has shown that five predominant acidic moieties may account for the observed potentiometric titrations in aqueous medium. Information from non-aqueous titrations and titrations in presence of excess metal ions, e.g. Cu(2+) and Eu(3+), has shown that three of the acidic moieties are carboxylic in nature while the other two are of alcoholic nature. A comprehensive description of the dissociation properties of natural organic acids, as ligands, is advocated as a pre-requisite step towards understanding their interaction with metal ions in the environment.
    Talanta 04/1995; 42(3):441-7. DOI:10.1016/0039-9140(95)01433-C · 3.51 Impact Factor
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    ABSTRACT: That the solution chemistry of humic substances is perturbed by ionic strength effects and functional group heterogeneity is now widely accepted. Application of the two-phase approach employing concepts from the Donnan equilibrium and the electrochemical unit cell had earlier postulated the ionic strength effects to be due to the presence of higher molecular weight moieties in the fulvic acid ''assemblage'' Potentiometric titrations of a number of aquatic fulvic and humic acids (isolated by an initial preconcentration on diethylaminoethyl (DEAE) cellulose prior to their adsorption on XAD-8 resins) are presented as a function of ionic strength and their molecular weight distributions. Even though an apparent correlation between molecular weight distribution and ionic strength effects was observed, for humic substances of similar molecular weight, ionic strength effects seem to increase with an increase in the polydispersity of the molecule.
    Environmental Science and Technology 03/1995; 29(3):622-8. DOI:10.1021/es00003a009 · 5.48 Impact Factor
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    ABSTRACT: The dissociation and metal ion binding properties of a soil fulvic acid have been characterized. Information thus gained was used to compensate for salt and site heterogeneity effects in metal ion complexation by the fulvic acid. An earlier computational scheme has been modified by incorporating an additional step which improves the accuracy of metal ion speciation estimates. An algorithm is employed for the prediction of metal ion binding by organic acid constituents of natural waters (once the organic acid is characterized in terms of functional group identity and abundance). The approach discussed here, currently used with a spreadsheet program on a personal computer, is conceptually envisaged to be compatible with computer programs available for ion binding by inorganic ligands in natural waters.
    Analytica Chimica Acta 02/1995; 302(2):309-322. DOI:10.1016/0003-2670(94)00491-4 · 4.52 Impact Factor
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    ABSTRACT: The acid-base properties of mycelium from Trichoderma harzianum were studied as a function of mass, state of mycelia, i.e., starved or nonstarved, and ionic strength of the aqueous phase. The nonstarved mycelia exhibited an extensive buffering behavior, which was attributed to the production of chemical species participating in the resultant equilibrium. Production of such ''acidic'' moieties resulted in higher acid capacities for the nonstarved mycelia (500-800 mequiv/kg mycelia) while for the starved mycelium, negative acid capacities were obtained (approximately -120 mequiv/kg mycelia) indicating a basic surface. Plots of charge balance versus pH showed an insensitivity to ionic strength changes and facilitated the estimation of the point of zero charge (pzc) for the starved mycelia. Similar plots for the nonstarved mycelia showed that this system was sensitive to ionic strength changes and yielded no distinguishable pzc values. It was assumed that the non-starved mycelium possibly allowed transport of ions into its cell wall structure or even intracellularly whereas the starved mycelium did not.
    Environmental Science and Technology 08/1994; 28(8):1502-5. DOI:10.1021/es00057a019 · 5.48 Impact Factor
  • C. Pettersson, J. Ephraim, B. Allard
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    ABSTRACT: Fulvic and humic acids were collected from groundwater and surface waters by an isolation procedure utilizing DEAE-cellulose, a weak anion exchange resin. DEAE-cellulose was selected since it can adsorb himics without any pH adjustment of the sampled water (in the pH range 4–8), thus making the method well suited for isolation of groundwater humic substances in the field. Characterization of general parameters (elemental composition, molecular weight, acidity, absorptivity, 14C-age) was performed on these humic substances as well as on humics isolated by other procedures. The humic weights and were divided into three categories on the basis of calculated atomic ratios, molecular weights and absorptivity: humic acids (high molecular weight) and fulvic acids (low molecular weight) from groundwater and surface waters, respectively. The similarities of the humics within each group, despite variations in age and origin, support the contention that humic substances have more properties in common than they have differences.
    Organic Geochemistry 05/1994; 21(5-21):443-451. DOI:10.1016/0146-6380(94)90096-5 · 2.83 Impact Factor
  • James H. Ephraim, Bert Allard
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    ABSTRACT: Despite the considerable number of publications in the literature, the interaction between humic substances and the Cu2+ metal ion is still of interest because the stability of the resultant complex coupled with the high reliability of the Cu2+-selectrode offers the possibility of obtaining very reliable data to facilitate modeling of the metal-humate systems. In this paper, the results of Cu2+ binding by a well characterised aquatic fulvic acid are presented in such a manner as to allow comparison with previously reported studies. In addition, these results obtained as a function of ionic strength (0.010 mol and 0.100 mol NaClO4) and fulvic acid to metal ion concentration ratios (FA/Cu2+ = 30, 6, 1) have been interpreted by considering the identified predominant ligand sites to give credence to the functionality assigned to them. Chemical speciation distributions have been obtained using MICROQL, a chemical equilibrium computer program.
    Environment International 01/1994; 20(1-20):89-95. DOI:10.1016/0160-4120(94)90071-X · 5.66 Impact Factor
  • Andrew S. Mathuthu, James H. Ephraim
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    ABSTRACT: The interaction between Ca(2+) and two well-characterized fulvic acids (Armadale and Laurentide FA) has been studied at 0.100 and 0.010M sodium nitrate using a fixed concentration of fulvic acid (100 ppm) and varying amounts of calcium (0.005-0.020 mmoles). Free calcium concentration was determined by in situ measurements employing a calcium electrode. For Armadale FA, free calcium was additionally determined via an ultrafiltration technique followed by atomic absorption measurements. For both fulvic acids, Ca(2+) binding was observed to be decreased by an increase in the ionic strength of the system. At the lower ionic strength the tendency for binding is dependent on the fulvic acid-to-metal ratio while at the higher ionic strength, the binding is insensitive to changes in the fulvic acid-to-metal ratio (an observation corroborating the contention that calcium binding to humic substances is primarily electrostatic). Comparison of the computed overall complex formation functions shows that values obtained from the ultrafiltration method were higher than those obtained using the calcium electrode. The binding of calcium was similar for the two fulvic acids.
    Talanta 05/1993; 40(4):521-6. DOI:10.1016/0039-9140(93)80011-F · 3.51 Impact Factor
  • James H. Ephraim
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    ABSTRACT: Zinc binding by a well characterized fulvic acid was studied by the ion-exchange distribution technique and ultrafiltration method at 0.100 M NaClO4 using trace amounts of zinc (≤ 10−1 M) and two different fulvic acid concentrations (6.2 × 10−4 and 1.2 × 10−3 M). The results were interpreted by considering the various acidic sites envisaged from potentiometric titrations in aqueous and non-aqueous media. In addition to calculating the overall complex formation function, literature-based constants for the complexation between the metal ion and the ascribed functional group were employed to account for the observed binding patterns as a function of pH. This supported the interpretation of the functional groups assigned to the envisaged acidic sites. Results from the ultrafiltration method were in agreement with those obtained from the ion-exchange distribution technique.
    Analytica Chimica Acta 09/1992; 267(1-267):39-45. DOI:10.1016/0003-2670(92)85004-P · 4.52 Impact Factor
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    ABSTRACT: Advances in safe management and disposal of radioactive waste have shown that a comprehensive program requires the incorporation of dissolved organics into radwaste and transport effluent models, with respect to their binding of radionuclides. The binding of Eu3+, Th4+ and UO22+ to a well-characterized aquatic fulvic acid has been studied using an ultrafiltration method at a bulk electrolyte concentration of 0.10 M NaClO4, trace amounts of radionuclides and fulvic acid concentrations of 60 and 120 mg/l. The results expressed as the overall complex formation function, βov, versus pH show the following order: Th4+ > Eu3+ > UO22+. The estimated βov, values have been discussed by considering the aqueous chemistry of Eu3+, Th4+ and UO22+ vis-à-vis the solution chemistry of the fulvic acid sample.
    MRS Online Proceeding Library 12/1991; 294. DOI:10.1557/PROC-294-759
  • James H. Ephraim, Jacob A. Marinsky
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    ABSTRACT: An ultrafiltration method was employed to study Fe(II)/Fe(III) and Cu(II) binding by Armadale Horizon fulvic acid. The results of the Fe—fulvate studies indicate the formation of “aggregates” between Fe and the fulvic acid molecule. The reduction of Fe(III) to Fe(II) by fulvic acid is also observed. Results for Cu(II)—fulvate electrode method. An algorithm developed previously for the prediction of metal ion binding by fulvic acid at different pH and salt concentration levels was tested further by comparing Cu2+ ion binding predictions with their measured values.
    Analytica Chimica Acta 05/1990; 232(1):171–180. DOI:10.1016/S0003-2670(00)81233-7 · 4.52 Impact Factor
  • James H. Ephraim, Michael M. Reddy, Jacob A. Marinsky
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    ABSTRACT: The development and refinement of a two-phase model for describing the potentionmetric properties of crosslinked weak acid polyelectrolyte gels and their linear analogues are discussed. Application of this approach has been facilitated by identifying functional group heterogeneity and separate phase effects as the major complications in the description of ion binding by humic substances. By their separation and quantification, equilibrium properties of these systems have been anticipated. This approach may be described as a "discrete ligand" model with solution chemistry effects taken into consideration. Examples of its applications are enumerated and an attempt is made to compare the approach with others.
    Humic substances in the aquatic and terrestrial environment, Proceedings of an International Symposium Linköping, Sweden, August 21-23, 1989, Lecture Notes in Earth Sciences, v. 33, pp. 263-276, Springer-Verlag, New York, Edited by Allard, B, Bóren, H, and Grimvall, A, 08/1989: pages 261-276; Springer-Verlag, New York..
  • J.H. Ephraim, H XU
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    ABSTRACT: An ultrafiltration technique has been adapted to obtain information on the binding of cadmium by a fulvic acid extracted from a deep groundwater. The results obtained are compared to those obtained by the ion-exchange distribution method (Schubert's approach) and an ion selective electrode method. The data obtained have been analyzed taking into consideration the heterogeneity of the fulvic acid sample. Results from the comparison indicate that with a proper design and conditioning of the diaflo membrane, the ultrafiltration technique offers a promising approach with respect to obtaining meaningful information on the binding of trace metals by natural organic acids.
    Science of The Total Environment 06/1989; 81-2:625-634. DOI:10.1016/0048-9697(89)90171-X · 3.16 Impact Factor
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    ABSTRACT: Fulvic acids have been recovered from three deep groundwaters and one surface water and characterized with respect to elemental composition, molecular weight, acid capacity and 14C-age. The corresponding waters are also characterized in detail. All of the fulvic acids, with ages varying from 0 to 5250 years, are very similar. The onlu significant difference between fresh and old materials are lower content of oxygen and nitrogen and higher COOH/OH-ratios for the materials from the old waters. Dating of the water using 14C-analysis of the dissolved organic material is probably better than using the carbonate as the 14C-source.
    Science of The Total Environment 06/1989; 81-82:287-296. DOI:10.1016/0048-9697(89)90135-6 · 3.16 Impact Factor

Publication Stats

376 Citations
81.24 Total Impact Points


  • 1988–1996
    • Linköping University
      • Department of Mathematics (MAI)
      Linköping, Östergötland, Sweden
  • 1993
    • University of Zimbabwe
      • Department of Chemistry
      Harare, Harare Province, Zimbabwe
  • 1986
    • University at Buffalo, The State University of New York
      • Department of Chemistry
      Buffalo, New York, United States