Humic acid potentiometric response patterns: out-of-equilibrium properties and species distribution modeling

Chemical and Biological Technologies in Agriculture

Table 1 Results (protonation constants, pKas, and mole number) for the calculation of species distribution models of the humic acid sample studied using the Best 7 program

Model	Standard^a	Costa et al.^b			Calculated model M1			Calculated model M2
Species		pKa	mmol.g⁻¹	%	pKa	mmol.g⁻¹	%	pKa	mmol.g⁻¹	%
Carboxylic	4.56	6.35	1.042	25	6.28	1.013	23	4.35	0.549	12
Phthalic	2.75	2.76	1.163	27	2.75	1.134	26	2.81	0.923	21
Phthalic	4.93	4.71			4.73			4.89
Phenolic	9.82	9.66	0.666	16	9.73	0.938	22	9.87	0.688	16
Catechol	9.23	7.97	0.540	13	7.92	0.549	13	8.87	0.492	11
Catechol	13.0	13.30			13.36			11.83
Salicylic	2.81	3.29	0.810	19	3.08	0.715	16	2.79	0.600	13
Salicylic	13.4	13.40			13.39			13.39
Supramolecular								6.65	1.147	26
Total			4.221			4.351			4.400