Effects of pH, ionic strength and heavy metal ions on UV spectras of humic acid

The structure characteristics of humic acids (HA) was analysed by studying the HA UV spectras affected by pH, ionic strength and the metal ions. And the relationships between E3/E4 and the pH and ionic strength of the solution were discussed. The results showed that the absorption band of the HA ultraviolet spectrum occurred blue shift mainly with the increase of pH value. But this influence with the pH gradually reduced until the pH had no effect with the increase of solution ionic strength. The absorption band of the HA ultraviolet spectrum occurred red shift and the absorption intensity increased with the increase of solution ionic strength. And the HA E3/E4 value and ionic strength had significant positive correlation. The absorption band of the HA ultraviolet spectrum happened with red shift with the increase of adding the concentrations of Cu²⁺ or Cd²⁺.