SELECTIVITY OF LIQUID MEMBRANE CADMIUM MICROELECTRODES BASED ON THE IONOPHORE N,N,N',N'-TETRABUTYL-3,6-DIOXAOCTANEDITHIOAMIDE

The selectivity of heavy metal ion-selective electrodes has often bee inadequately characterized in the past. Only recently, alternative met hods have become available to assess the response toward highly discri minated ion solutions. In this article, the selectivity of vibrating l iquid membrane cadmium-selective microelectrodes was characterized usi ng the separate solution method, the fixed interference method, the ma tched potential method. and Bakker's method which demands one to condi tion the electrode membrane in discriminated ion solutions prior to me asurement. Tn this study, the matched potential method gave selectivit y values for the two least discriminated ions, lead(II) and copper(II) , that were comparable to the ones obtained with SSM. Bakker's method, on the other hand: was the only method that reveals the extremely hig h ion selectivity over all other discriminated ions. This study shows that carrier-based cadmium microelectrodes possess sufficient selectiv ity for many in situ applications, and that experimental biases may so metimes lead to experimental selectivity coefficient variations of abo ut 12 orders of magnitude depending on the chosen method.