Vapor-pressure osmometric study of the molecular weight and aggregation tendency of a reference-soil fulvic acid |
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Authors: | Jacob A Marinsky Michael V Reddy |
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Institution: | U.S. Geological Survey, Denver Federal Center, Lakewood, CO 80225 U.S.A. |
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Abstract: | The molecular weight and aggregation tendency of a reference-soil fulvic acid in Armadale horizon Bh were determined by vapor-pressure osmometry using tetrahydrofuran and water as solvents. With tetrahydrofuran, number-average molecular weight values of 767 ± 34 and 699 ± 8 daltons were obtained from two separate sets of measurements. Two sets of measurements with water also yielded values within this range (754 ± 70 daltons) provided that the fulvic acid concentration in water did not exceed 7 mg ml?1; at higher concentrations (9.1–13.7 mg ml?1) a number-average molecular weight of 956 ± 25 daltons was resolved, providing evidence of molecular aggregation. Extension of these studies to 80% neutralized fulvic acid showed that a sizeable fraction of the sodium counter ion is not osmotically active. |
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