Hej everyone,
I'm working with humic substances in soil amendments. Last year, I outsourced measurements for fulvic and humic acids to a lab. After months, I sent freshly made samples to a Chinese partner, who analyzed them again and the results were consistently and significantly lower than those of the lab.
I do not yet know which methods were used by the Chinese partner, because it was a Chinese standard whose translation I can't find. However, the lab used a colorimetric method (UV-Vis spectroscopy) that I think overestimated the concentration of fulvic acids at least.
Does anyone have experience with these methods and/or can suggest better ones to measure fulvic acids?
I am unaware of the purity percentage of the humic acid you purchased, as I have noticed that reagent suppliers offer a variety of different purity levels ranging from 10% to 95%. The basis for colorimetric methods lies in the benzene rings within humic acid that can absorb ultraviolet light; if your raw material's purity is not high, other impurities may lead to increased absorption during testing. In order to accurately quantify humic acid (as a substance with a defined structure), you could use a highly purified substance from a trustworthy reagent supplier to establish a standard curve and then conduct quantitative analysis using High-Performance Liquid Chromatography (HPLC).
I have found that in China, the common method for determining humic acid involves potassium dichromate oxidation, which is based on the measurement of phenolic hydroxyl groups. However, it's equally true that any impurities within the sample can indeed affect the test results. Additionally, it's unclear whether your sample requires acid treatment prior to extraction; if so, this process could also potentially influence the outcome.
Use Lamar Standardized Method or the Larry G. Butler Method for quantifying fulvic acids
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