Lowering the Detection Limit of Solvent Polymeric Ion-Selective Membrane Electrodes. 2. Influence of Composition of Sample and Internal Electrolyte Solution

• Published in: Analytical chemistry (Washington) Vol. 71; no. 6; pp. 1210 - 1214
• Main Authors: Sokalski, Tomasz, Ceresa, Alan, Fibbioli, Monia, Zwickl, Titus, Bakker, Eric, Pretsch, Ernö
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15.03.1999
• Subjects: Chemistry; Electrochemistry; Electrodes: preparations and properties; Exact sciences and technology; General and physical chemistry; Ion selective electrodes; Ions; Membranes; Organic chemistry; Membrane electrode; Lead ion; Electrolyte solution; Metal Ions; Electrochemical activity; Composition effect; Electromotive force; Experimental study; Alkaline earth metal Ions; Ion selective electrode; Electrochemical properties; Calcium ion; Ionic selectivity; Detection limit; Concentration effect; Aqueous solution; Electrode potential
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac9809332

The influence of the composition of the internal electrolyte solution on the response of Pb2+- and Ca2+-selective membrane electrodes is investigated. It is shown that the lower detection limit is improved by generating, in the membrane, ionic gradients that lead to a flux of primary ions toward the inner reference electrolyte solution. If the ion flux is too strong, it may cause analyte depletion at the membrane surface and, as a consequence, apparent super-Nernstian response. Such electrodes are not adequate to measure low analyte activities but can be used to determine unbiased selectivity factors. The results are interpreted in terms of a steady-state model, introduced in the companion paper, that describes the influence of concentration gradients generated by ion-exchange and coextraction processes on both sides of the membrane.