Reduction of chloride ion interference in chemical oxygen demand (COD) determinations using bismuth-based adsorbents

An efficient method for the reduction of chloride interference in the determination of chemical oxygen demand (COD) without the use of Hg(II) as a masking agent is described. Chloride ion is removed as hydrochloric acid gas from acidified sample solutions at 150°C in a closed reaction tube and captured by a bismuth-based adsorbent suspended above the heated solution. The effects of adsorbent composition, sulfuric acid concentration, reflux time, chloride concentration, and Ag(I) catalyst on the efficiency of the removal of chloride ion and the COD determination are discussed. The viability of the approach is demonstrated using a wastewater sample.