Experimental Conditions Concerning Potentiometric Titration of Humic Acid

Abstract

The humic acids of four soils from Denmark have been extracted by EDTA. The humic acids were separated from EDTA by precipitation with Baa+. The ash content was lowered by treatment with HF and HC1. The ash content in the four humic acids was less than 0-6 per cent. Chemical analysis of the humic acids supply some evidence for the suggestion that EDTA extracted organic matter is a more definite fraction than humic acid extracted by NaOH.It was shown that an alkaline humate solution stored in sterile, sealed ampoules under N, does not change its initial pH, indicating that the protolytic equilibrium is established instantly. It is therefore proposed that the titration of humic acid should be carried out as quickly as a normal acid-base titration.

Dependence on molecular weight of acid-base properties of humic and fulvic acids

“…The stability of HS in alkaline solutions is a debated question, since literature supporting instability [11][12][13][14], as well as stability [15][16][17] can be found. According to our findings, poor stability appears to be a general characteristic, since it was observed both in the HA and in the FA different fractions.…”

Titrations of Fulvic Acid Fractions Ii: Chemical Changes at High Ph

“…On the other hand, Borggaard (1974), while investigating some relatively ash-free humic substances found that their solutions were stable at high pH in the absence of 0,. Our results show that the polycarboxylic acid component of fulvic acid (fraction 11) was chemically altered in alkaline solution by reactions quite distinct from oxidative degradation, but we have been unable to shed much new light on what reaction mechanisms are likely to be involved.…”