Trace analysis at clay‐modified carbon paste electrodes

Carbon paste electrodes modified with montmorillonite clay are used for the collection of iron(III) from dilute solutions followed by voltammetric quantification of the surface‐bound cation. Open‐circuit conditions are maintained during the ion exchange preconcentration. The surface is regenerated by a brief exposure to a sodium carbonate solution. For 20 preconcentration/measurement/regeneration cycles, the response could be reproduced with 4.8% relative standard deviation. Factors influencing the response, such as electrode composition, preconcentration time, measurement and „cleaning”︁ solutions, ionic strength, coexisting metals, iron concentration, and other variables, have been investigated. A detection limit of 0.2 mg/liter was estimated following 3 min preconcentration. The unusual mechanisms of ion exchange processes at clays should lead to a new class of modified electrodes for preconcentration/voltammetric measurements.