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Preliminary theoretical studies revealed the selective complexation of bis (2-mercaptoanil) diacetyl (BMDA) with La 3 over several alkali, alkaline earth and heavy metal ions. Thus, novel PVC-based membrane (PBM) and coated graphite membrane (CGM) sensors for La(III) based on BMDA were prepared. The electrodes display Nernstian behavior over wide concentration ranges (i.e., 1.0 Â 10 À5 ± 1.0 Â 10 À1 M for PBM and 1.0 Â 10 À6 ± 1.0 Â 10 À1 M for CGM). The potential response of sensors was pH independent in the range of 4.0 ± 8.0. The sensors possess satisfactory reproducibility, fast response time ( < 15 s), and specially excellent discriminating ability for La 3 ions with respect to most of the cations. The membrane sensor was used as an indicator electrode in potentiometric titration of lanthanum ions with EDTA. The coated graphite membrane electrode was applied in determination of fluoride ions in mouth wash preparations.

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A PVC membrane electrode based on a cadmium-salen (N,N'-bis-salicylidene-1,2-ethylenediamine) complex as an anion carrier is described. The electrode has an anti-Hofmeister selectivity sequence with a preference for thiocyanate at pH 1.5-11.0. It has a linear response to thiocyanate from 1.0 x 10(-6) to 1.0 x 10(-1) mol L(-1) with a slope of 59.1 +/- 0.2 mV per decade, and a detection limit of 7 x 10(-7) mol L(-1). This electrode has high selectivity for thiocyanate relative to many common organic and inorganic anions. The proposed sensor has a fast response time of approximately 15 s. It was applied to the determination of thiocyanate in a milk sample.

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