High-performance liquid chromatographic determination of humic acid in environmental samples at the nanogram level using fluorescence detection

A high-performance liquid chromatographic method for the determination of humic acid in environmental samples is presented. The humic acid is chromatographed as its sodium or calcium complex, eluting as a single, sharp peak. Coral skeletal matter, sea water, river water, soils and plant matter were successfully analysed. The detection limit is 15 ng. The relative standard deviation for a coral skeletal sample is 1.9%. Unusual chromatographic properties such as the occurrence of peak broadening with increased concentration appear to be due to a slow change in the equilibrium composition of humic acid. In solution, fulvic acid showed similar properties to humic acid.