Prometrine - humic acids interactions studied at a water/1,2-dichloroethane interface

Abstract

The interaction of the herbicide prometrine (PROM) with humic acids (HA) in water was analyzed at a pH range between 2.00 to 10.00. For this purpose the transfer current of protons facilitated by PROM across a water/1,2-dichloroethane interface was employed to quantify PROM concentration in absence or in presence of HA. When humic acids were added in increasing amounts to the solution containing PROM, a gradual decrease in current values was observed, evidencing the retention of PROM by HA. This effect was more important at high pH values. From the results it is concluded that the adsorption of PROM is dependent on the pH and HA concentration. At high pH values the herbicide is strongly retained by HA, revealing a strong interaction probably due to the possibility of PROM (neutral species) to access to hydrophobic regions of AH, where van der Waals interactions prevail. The amount of PROM bounded to HA was calculated by subtracting peak current values in presence and in absence of HA and the adsorption isotherm was plotted. The concave or S type curves obtained, indicative of a process with high resistance to adsorption at low concentrations, was fitted with Freundlich isotherm.