Fast Detection of Lead Dioxide (PbO_2) in Chlorinated Drinking Water by a Two-Stage lodometric Method

摘要

Lead dioxide (PbO_2) is an important corrosion product associated with lead contamination in drinking water. Quantification of PbO_2 in water samples has been proven challenging due to the incomplete dissolution of PbO_2 in sample preservation and digestion. In this study, we present a simple iodometric method for fast detection of PbO_2 in chlorinated drinking water. PbO_2 can oxidize iodide to form triiodide (I_3~-), a yellow-colored anion that can be detected by the UV-vis spectrometry. Complete reduction of up to 20 mg/L PbO_2 can be achieved within 10 min at pH 2.0 and Kl = 4 g/L Free chlorine can oxidize iodide and cause interference. However, this interference can be accounted by a two-stage pH adjustment allowing free chlorine to completely react with iodide at ambient pH followed by sample acidification to pH 2.0 to accelerate the iodide oxidation by PbO_2. This method showed good recoveries of PbO_2 (90-111%) in chlorinated water samples with a concentration ranging from 0.01 to 20 mg/L. In chloraminated water, this method is limited due to incomplete quenching of monochloramine by iodide in neutral to slightly alkaline pH values. The interference of other particles that may be present in the distribution system was also investigated.