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ARS Home » Midwest Area » Ames, Iowa » National Laboratory for Agriculture and The Environment » Soil, Water & Air Resources Research » Research » Publications at this Location » Publication #301477

Title: Determination of humic and fulvic acids in commercial solid and liquid humic products by alkaline extraction and gravimetric determination

item LAMAR, RICHARD - Horizon Ag-Products, Lp
item Olk, Daniel - Dan
item MAYHEW, LAWRENCE - Eco Agri-Minerals
item BLOOM, PAUL - University Of Minnesota

Submitted to: Journal of AOAC International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2014
Publication Date: 5/20/2014
Publication URL:
Citation: Lamar, R.T., Olk, D.C., Mayhew, L., Bloom, P.R. 2014. Determination of humic and fulvic acids in commercial solid and liquid humic products by alkaline extraction and gravimetric determination. Journal of AOAC International. 97(3):721-730.

Interpretive Summary: Liquid and solid humic products are sold commercially as means to improve crop growth. Their production is not regulated, and currently there is no widely accepted method for measuring their contents. Multiple procedures do exist but all are known to have limitations. We developed and tested an improved method that can be performed with common laboratory equipment. It gives consistent estimates of the product contents and in contrast to all other procedures it can distinguish humic products from other, less expensive materials that might be falsely marketed as humic products. This work provides a method that will allow state government regulators to confirm advertised claims of product contents, so its widespread acceptance should foster sales of products shown to be genuine and free of falsified materials. The humic product industry and their customers will benefit from this work by having more accurate estimates of product contents.

Technical Abstract: Increased use of humic substances in agriculture has generated intense interest among producers, consumers, and regulators for an accurate and reliable method for quantification of humic (HA) and fulvic acids (FA) in raw ores and products. Here we present a thoroughly validated method, the Humic Products Trade Association (HPTA) Method for determination of HA and FA contents in raw humate ores and in solid and liquid products produced from them. While the method uses classical alkaline extraction followed by acidification to separate HA from FA, it differs from previous methods in that it determines HA and FA concentrations on an ashfree basis and narrowly defines FA as that part of the extract that remains after HA precipitation, which binds to a hydrophobic, nonionic macroporous acrylic ester resin. Critical steps in the method, e.g., initial sample mass, sample 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.