Acid-base properties of fractionated humic acids

journal article - other

English

Humic acids (HA) were fractionated by their dissolution in universal buffers (NaOH, H3BO3, H3PO4 and CH3COOH) with various pH-values. Obtained fractions were characterized by UV/VIS and FT-IR spectroscopy and their acid-base properties were studied. It was found that contain of acidic groups in majority of individual fractions is higher than the content of original HA samples. Our hypothesis is that HA structure is changed during fractionation. HA can interact with individual components of buffer and re-arranged their structure, which results in apparently higher acidity of obtained fractions. The re-arrangement of HA structure probably causes, that some acidic groups inside HA aggregates, which are not able dissociate in original HA sample, can contribute to measured acidity in individual fractions. Surprising result is that residue after dissolving original HA in very alkaline buffer (pH = 12) has after fractionation (and "exhaustion" of the largest amount of HA fraction) several times higher solubility in water as others. On the other hand, this fact corresponds with our hypothesis of re-arrangement and possible interactions with buffer, because the most "aggressive" buffer caused the most marked changes in HA properties.

humic acids, fractionation, acid-base properties

KLUČÁKOVÁ, M.; PILNÝ, O.

2008

9. 9. 2008

Brno

1213-7103

Chemické listy

102

S

Czech Republic

s1156

s1157

2