The reactions of paraquat and divalent metal ions with humic acid: Factors influencing stoichiometry 2 |
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Authors: | Luis E Sojo Donald S Gamble Cooper H Langford Raymond H Zienius |
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Institution: | 1. Chemistry and Biotechnology Research , International Corporation , P.O. Box 2010, 101–9865 WestSasnich Road, Sidney, British Columbia, V8L 3S3;2. Land Resource Research Centre , Agriculture Canada , Ottawa, Ontario, K1A OC6;3. Department of Chemistry and Biochemistry , Concordia University , 1455 Boulevard de Maisonneuve West, Montréal, Québec, H3G 1M8 |
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Abstract: | 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 samples. It should be possible to develop analytical chemical methods for characterizing the stoichiometric properties of humic acid samples. |
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Keywords: | Paraquat Humic Acid Stoichiometry Equivalence Points Aggregation Precipitation |
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