A New Standardized Method for Measuring Humic and Fulvic Acid Concentrations in Commercial Products.

Commercially available humic products consisting of various combinations of humic acid (HA) and fulvic acid (FA) are used for increasing the use efficiency of fertilizers and environmental remediation. Until recently, the growth of the humic products industry was constrained by the lack of a validated analytical procedure for determining the content of humic and fulvic acids in commercial products.  In response, the Humic Products Trade Association (HPTA) has developed a validated method for determination of HA and FA contents in raw humate ores and in solid and liquid products produced from them. The method involves alkaline extraction followed by acidification to separate HA from the fulvic fraction.  This is followed by separation of FA through adsorption on a nonionic resin at acid pH to distinguish the FA from more hydrophilic soluble compounds such as carbohydrates.  It differs from previous methods in that it determines HA and FA concentrations gravimetrically on an ash-free basis. 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.  The Method Detection Limits (MDLs) for HA and FA are 4.62 mg L^-1 and 4.8 mg L^-1, respectively.  The Method Quantitation Limits (MQLs) for HA and FA are 14.7 mg L^-1 and 15.3 mg L^-1, respectively. The procedure has been used to distinguish commercial humic products from potential adulterants, including molasses, coal, and lignosulphonates.

The method developed by HPTA has been accepted by U.S. state fertilizer regulators as an official procedure.  Currently it is moving through the validation process of the International Organization for Standardization (ISO), which includes independent analyses of samples by 12 laboratories in five countries.