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Why Are Humic Substances Called Acids?

By Richard Lamar, PhD
Senior Director of Humic Research
Bio Huma Netics, Inc.

We are accustomed to seeing humic substances (humic and fulvic) in dry/granular form, and we tend to think of acids as liquids. So why are humic and fulvic substances called acids?

All substances, solid AND liquid, have a chemical makeup. An acid is a chemical that can donate a proton (H+) to a water molecule (H2O, which would form H3O+) or to another chemical such as ammonia (NH3, which would form NH4+).

Organic acids are generally weak acids that do not completely dissociate (i.e., donate a proton) in water in the way that strong mineral acids do, such as in the case of hydrochloric acid (HCl). The most common organic acids are carboxylic acids, sulfonic acids, phenols and alcohols (Figure 1).

Organic acids can be aliphatic (structured as open chains rather than aromatic rings), such as acetic acid (Fig. 1A) or ethanol (Fig. 1E). Organic acids can also be aromatic (made up of ring structures, originally named so because of their fragrant properties), such as benzoic acid (Fig. 1B), benzene sulfonic acid (Fig. 1C) or phenol (Fig. 1D).

All of these structures can be found in humic and fulvic acids, sometimes all in the same molecule. For example, one humic acid or fulvic acid molecule might contain a benzoic acid, a phenol, an alcohol, and an aliphatic carboxylic acid (Figure 2). All of these functional groups can ionize (i.e., lose their H+ atoms and contribute to acidity) (Figure 3). The primary factor affecting ionization of organic acids is pH.

Figures 1–3. Chemical structures found in organic acids

We will discuss the interrelationship of soil, pH, and humic substances in Humic Corner #4.

What Differentiates Humic and Fulvic Acids?

By Richard Lamar, PhD
Director of Humic Research
Bio Huma Netics, Inc.

For centuries, humic acids (HA) were thought to be composed of much larger molecules than those found in fulvic acids (FA). However, the application of Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS), which separates molecules on the basis of molecular weight, demonstrates that the molecular weights of the two fractions both fall in the range of 200–800 Daltons (Da), with most of the molecules having molecular weights in the range of 200–400 Da (Figure 1). To give context, carbon (C) weighs 12 Da, oxygen (O) weighs 16 Da, and hydrogen (H) weighs 1 Da. Thus, phenol molecules (an aromatic organic compound, also called carbolic acid), which have 6 C, 1 O, and 11 H atoms, weigh 99 Da. [Read more…]

JoVE Video Journal Publication: Quantification of Humic and Fulvic Acids

Dr. Richard T. Lamar and Dr. Hiarhi Monda of our Humic Research Laboratory, with assistance from analytical chemist Ryan Fountain, have published a methodology video in the biochemistry section of the peer-reviewed online video journal, JoVE.

The video, Quantification of Humic and Fulvic Acids in Humate Ores, DOC, Humified Materials and Humic Substance-Containing Commercial Products, shows the step-by-step laboratory methodology (the New Standard Method) for gravimetric quantification of humic substances (e.g., humic and fulvic acids) on an ash-free basis, in dry and liquid materials from soft coals (i.e., oxidized and non-oxidized lignite and sub-bituminous coal), humate ores and shales, peats, composts and commercial fertilizers and soil amendments.

In the video introduction, Dr. Lamar states, “The New Standard Method for quantification of humic acids provides a more accurate and precise analysis compared to the existing regulatorily accepted methods, and it also provides a standard method for pure hydrophobic fulvic acid quantification. The advantage of this protocol is that it provides a gravimetric analysis of humic and hydrophobic fulvic acid concentrations on an ash-free basis, and the extraction process has been optimized to obtain the highest recoveries of both humic and fulvic acids from samples.

At the video’s conclusion, Dr. Monda states, “Following this procedure, the dry humic and fulvic acids obtained can be used for characterization purposes, such as the carbon-13 and the proton NMR electron resonance, and the ultrahigh resolution mass spectrometry, among other useful techniques. This can be used for characterization of the humus chemistry, as well as being a useful tool to dig deep into the structure-activity relationship with plant fitness and the underlying plant defense mechanisms.

Direct link to video on the JoVE Website: https://www.jove.com/v/61233/quantification-humic-fulvic-acids-humate-ores-doc-humified-materials (A free subscription will be required to view the entire video on the JoVE Website.)

From the JoVE Website: Filmed at the world’s top scientific institutions, JoVE videos bring to life the intricate details of cutting-edge experiments enabling efficient learning and replication of new research methods and technologies. JoVE is a peer-reviewed scientific video journal that is indexed in PubMed and Web of Science.

Our Humic Advantage

Humic substances, among the most wondrous products of nature, are the recycled essential residues of life. Plants harvest the sun’s energy and create life from that energy plus the carbon and oxygen they pull out of the air and the minerals they pull out of the soil. When plants die, all of their components are decomposed through the aid of microorganisms and mineralization, then returned to the soil as organic matter. Continue reading

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