![]() This suggests that as the HA carboxylic acid functional groups form inner sphere complexes with divalent cations, intramolecular interactions result in a contraction of the HA molecular structure, thereby preventing PRODAN from associating with the condensed aromatic, electron accepting moieties inherent within HA molecules and responsible for PRODAN quenching. Cation concentrations below the HA charge density resulted in the greatest decrease of PRODAN quenching, while very little additional decrease in PRODAN quenching occurred at cation concentrations above the HA charge density. However, interactions between PRODAN and HA decreased in the presence of cations at pH 7 and 10. ![]() ![]() Regardless of pH and cation concentration, PRODAN quenching by FA was unaffected by cations. The influence of cations (Na(+), Ca(2+) and Mg(2+)) on noncovalent interactions between 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and dissolved fulvic acids (FAs) (Norman landfill leachate fulvic acid (NLFA) and Suwannee River fulvic acid (SRFA)) and dissolved humic acids (HAs) (Suwannee River humic acid (SRHA) and Leonardite humic acid (LHA)) was examined using steady-state fluorescence spectroscopy at pH 4, 7 and 10 as a function of cation concentration (up to 25-100mM). Influence of cations on noncovalent interactions between 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and dissolved fulvic and humic acids. The method quantitation limits for HA and FA were 14.7 and 15.3 mg/L, respectively. The method detection limits for HA and FA were 4.62 and 4.8 mg/L, respectively. Critical steps in the method, e.g., initial test portion mass, test portion to extract volume ratio, extraction time, and acidification of alkaline extract, were optimized for maximum and consistent recovery of HA and FA. It differs from previous methods in that it determines HA and FA concentrations gravimetrically on an ash-free basis. This is followed by separation of FA from the fulvic fraction by adsorption on a nonionic macroporous acrylic ester resin at acid pH. The methods used for preparation of HA and FA were adapted according to the guidelines of the International Humic Substances Society involving alkaline extraction followed by acidification to separate HA from the fulvic fraction. Here we present a thoroughly validated method, the new standardized method for determination of HA and FA contents in raw humate ores and in solid and liquid products produced from them. Increased use of humic substances in agriculture has generated intense interest among producers, consumers, and regulators for an accurate and reliable method to quantify humic acid ( HA) and fulvic acid (FA) in raw ores and products. Lamar, Richard T Olk, Daniel C Mayhew, Lawrence Bloom, Paul R A new standardized method for quantification of humic and fulvic acids in humic ores and commercial products.
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