(1)
Anđelković, T.; Perović, J.; Blagojević, S.; Purenović, M.; Nikolić, R.; Bojić, A.; Anđelković, D. Acidity of Humic Acid Related to Its Oxygen-Containing Functional Groups. Maced. J. Chem. Chem. Eng. 2006, 25, 131-137.