Quantification of Humic and Fulvic Acids in Humate Ores, DOC, Humified Materials and Humic Substance-Containing Commercial Products

Abstract

The purpose of this method is to provide an accurate and precise concentration of humic (HA) and/or fulvic acids (FA) in soft coals, humic ores and shales, peats, composts and humic substance-containing commercial products. The method is based on the alkaline extraction of test materials, using 0.1 N NaOH as an extractant, and separation of the alkaline soluble humic substances (HS) from nonsoluble products by centrifugation. The pH of the centrifuged alkaline extract is then adjusted to pH 1 with conc. HCl, which results in precipitation of the HA. The precipitated HA are separated from the fulvic fraction (FF) (the fraction of HS that remains in solution,) by centrifugation. The HA is then oven or freeze dried and the ash content of the dried HA determined. The weight of the pure (i.e., ash-free) HA is then divided by the weight of the sample and the resulting fraction multiplied by 100 to determine the % HA in the sample. To determine the FA content, the FF is loaded onto a hydrophobic DAX-8 resin, which adsorbs the FA fraction also referred to as the hydrophobic fulvic acid (HFA). The remaining non-fulvic acid fraction, also called the hydrophilic fulvic fraction (HyFF) is then removed by washing the resin with deionized H2O until all nonabsorbed material is completely removed. The FA is then desorbed with 0.1 N NaOH. The resulting Na-fulvate is then protonated by passing it over a strong H+-exchange resin. The resulting FA is oven or freeze dried, the ash content determined and the concentration in the sample calculated as described above for HA.