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Sökning: WFRF:(Ephraim James)

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2.
  • Dahlén, Johan, et al. (författare)
  • Determination of the molecular weight of fulvic acids by UV/VIS spectroscopy
  • 1999
  • Ingår i: Chemosphere. - 0045-6535 .- 1879-1298. ; 38:4, s. 783-794
  • Tidskriftsartikel (refereegranskat)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 UVNIS 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.
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3.
  • Nordén, Maria, et al. (författare)
  • Interaction of Strontium and Europium with an Aquatic Fulvic Acid Studied by Ultrafiltration and lon Exchange Techniques
  • 1991
  • Ingår i: Humic substances in the aquatic and terrestrial environment : proceedings of an international symposium, Linköping, Sweden, August 21-23, 1989. - Berlin Heidelberg New York : Springer. - 3540537023 ; , s. 297-303
  • Bokkapitel (refereegranskat)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 meta! concentrations (trace levels) and constant FA concentration. In the Sr-FA system the bound meta! 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 meta! 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.
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