Polarographic determination of benzotriazoles and their sorption behavior on granular activated carbon

Abstract

Because of their persistence and unknown environmental risks, the widespread occurrence of benzotriazoles has been gaining increased attention. A highly selective, rapid, and economical method—differential pulse polarography—was developed and applied for the quantitation of commercially significant methylbenzotriazole isomers in environmental samples of relevance to wastewater treatment, non-point source pollution and acid mine drainage. Differential pulse polarography was able to accurately measure aqueous methylbenzotriazole, as well as the methylbenzotriazole fraction that sorbed to activated sludge biomass, subsurface sediments, and activated carbon. Granular activated carbons were characterized for their ability to sequester benzotriazoles from aqueous environments using differential pulse polarography and high-performance liquid chromatography. Langmuir, Freundlich, Toth and Redlich–Peterson isotherm models were compared for their ability to describe benzotriazole partitioning to granular activated carbons under a relatively wide range of water quality conditions. Sorption behavior of 5-methylbenzotriazole was best-described by a Redlich–Peterson isotherm model, where water quality parameters were varied in the following range pH (1 < pH < 5), temperature (5 °C < T < 25 °C), and in the following ranges of an ionic strength (0.005 < M < 0.02). 4- and 5-methylbenzotriazole concentrations determined by differential pulse polarography correlated well with those concentrations measured by high-performance liquid chromatography through an environmentally significant range (0.4–30 mg/L). Using a static mercury drop electrode, the method detection limit was 50 and 40 μg/L for 4- and 5-methylbenzotriazole, respectively. The developed DPP polarographic method was found to be simple, rapid, and it can be applied directly to environmental samples without filtration, extraction, and centrifugation.