Fig. 2. FT-IR spectra of humic substances. NaP, trisodium phosphate dodecahydrate; WHa, Waskish peat reference humic acid; EHa, Elliott soil standard humic acid; WFa, Waskish peat reference fulvic acid; EFa, Elliott soil standard fulvic acid; PHa, Pahokee peat reference humic acid; LHa, Leonardite standard humic acid.