Hydrogen Chloride Improved Selectivity of Lead Ionic Selective Electrode (Pb‐ISE) under High Calcium Concentration

Abstract

Leachants from the toxic characteristic leaching procedure (TCLP) of combustion residues, fly ash, usually contain calcium and lead ions as high as to 12000 and 1000 ppm, respectively. In this paper, the authors used a commercialized lead(II) ionic-selective electrode (Pb-ISE) to measure the lead(II) concentrations in such leachants and observed a serious interference from calcium(II) ions. The interference starts at the concentration ratio of ([Ca]/[Pb]) in the sample over 2.0. Reasons for the interference are not clear, but it can be suppressed by adding a chemical modifier, HCl(aq) solution, into the sample. The authors have found that the optimized addition amount in TCLP leachants is 4 mL of HCl(aq) per 20 mL sample, and the detection limit of the Pb-ISE was 5.2 ppm.