APA 6th Edition Zuman, P. i Rupp, E.B. (2006). Humic Acids – Are They Natural Products?. Croatica Chemica Acta, 79 (1), 57-65. Preuzeto s https://hrcak.srce.hr/2602
MLA 8th Edition Zuman, Petr i Elinore B. Rupp. "Humic Acids – Are They Natural Products?." Croatica Chemica Acta, vol. 79, br. 1, 2006, str. 57-65. https://hrcak.srce.hr/2602. Citirano 12.04.2021.
Chicago 17th Edition Zuman, Petr i Elinore B. Rupp. "Humic Acids – Are They Natural Products?." Croatica Chemica Acta 79, br. 1 (2006): 57-65. https://hrcak.srce.hr/2602
Harvard Zuman, P., i Rupp, E.B. (2006). 'Humic Acids – Are They Natural Products?', Croatica Chemica Acta, 79(1), str. 57-65. Preuzeto s: https://hrcak.srce.hr/2602 (Datum pristupa: 12.04.2021.)
Vancouver Zuman P, Rupp EB. Humic Acids – Are They Natural Products?. Croatica Chemica Acta [Internet]. 2006 [pristupljeno 12.04.2021.];79(1):57-65. Dostupno na: https://hrcak.srce.hr/2602
IEEE P. Zuman i E.B. Rupp, "Humic Acids – Are They Natural Products?", Croatica Chemica Acta, vol.79, br. 1, str. 57-65, 2006. [Online]. Dostupno na: https://hrcak.srce.hr/2602. [Citirano: 12.04.2021.]
Sažetak Alkaline cleavage of soil organic matter was studied by following the changes in absorbance at 250–270 nm, but particularly using differential pulse polarography. The measurement of peak currents obtained by the latter technique allowed to follow changes in concentration of CH3Oand HO-substituted benzaldehydes as well as of α,β-unsaturated ketones with time directly in the suspension of soil. Kinetics of the cleavage of the organic materials from soil and in particular its pH-dependence, were similar to that of cleavage of lignin, but different from those obtained with samples of humic acids. Based on this comparison and on discussion of chemical processes taking place during procedures used for isolation of humic acids from soils and waters, it is strongly indicated that humic acids are man-made macromolecular species rather than natural products.