Cadmium ion activity in soils: evaluation of cadmium ion-selective electrode

Cadmium ion activity was measured in 0.05 M Ca(NO/sub 3/)/sub 2/ extracts of two soils containing up to 100 ppM Cd. Comparative analyses by atomic absorption spectroscopy showed excellent agreement with the electrode method (r = 0.99, b = 1.03), suggesting the bulk of soluble Cd in solution was Cd/sup 2 +/ ions. Interference phenomena associated with the electrode were characterized. Cleaning the electrode by machine buffing and/or washing in EDTA was necessary for reproducible readings. Interference in soil extracts was primarily due to loosely adsorbed Cd, Pb, Cu, and Zn ions on the electrode surface. The detection limit of the electrode in soil extracts was 0.05 ..mu..g Cd/mL. The electrode cannot be used for analysis of soils containing highly concentrated Pb/sup 2 +/, Hg/sup 2 +/, Cu/sup 2 +/, or Ag/sup +/.