How to Test if Potassium Humate Products Or Sodium Humate Products Contain Potassium Fulvate Or Not?

Nowadays, many potassium humate acid or sodium humate products in the market are claimed to contain potassium fulvate.
Many buyers may wonder if there are any good test methods to judge if the product really contains potassium fulvate.
In fact, as long as we understand the characteristics of potassium fulvate, we can easily carry out the qualitative test below to identify whether the product contains potassium fulvate or not.

Please kindly note that some other rigid tests are to be done if a quantitative result is needed.
Potassium fulvate obtained from leonardite is the component with the smallest molecular weight among humic acid products.
It is soluble in both acid and alkali. Others like pyrotomalenic acid and brown humic acid are insoluble in acid. This property can be employed to easily identify whether the tested humic acid product contains potassium fulvate or not.

Method: Take 0.1g of the tested sample and dissolve it in 1000ml of water (either tap water or pure water can do), dilute to 10000 times, add a small amount of sulfuric acid (or hydrochloric acid or nitric acid), to a PH value of about 2-3, keep a static duration of 10 minutes, then filter to observe the color of the filtrate and residues on the filter paper. The darker the color of the filtrate is, the higher the content of potassium fulvate is contained; the more residues on the filter paper, the lower the content of potassium fulvate is.

Comparison picture of the two 1:10000 dilutions of sodium humate sample 1 (left) (potassium fulvate content <1%) and sodium humate sample 2 (right) (fulvic acid content >45%)