Polymer membrane electrodes, selectivity evaluation

In practice, the selectivity of polymer membrane electrodes can be evaluated using the well known Nicolsky equation ... 

V.J. Wotring, PK. Prince, L.G. Bachas, Evaluation of poly(vinylidene chloride) as a matrix for polymer membrane ion-selective electrodes. Analyst, 116, 581-584,1991. 

Another aspect of tin as a constituent of electrode material is shown by tin(IV)TPP complexes incorporated into PVC membrane electrodes. These increase the selectivity to salicylate over anions such as Cl-, Br- I-, I()4, Cl()4, citrate, lactate and acetate. The specificity is attributed to the oxophilic character of the Sn ion in TPP at the axial coordination sites. Indeed, carboxyl groups incorporated into the membrane polymer compete for these binding sites. The complete complex structure is important. Substitution of TPP with octaethylporphirine results in loss of salicylate selectivity231. Preparation and analytical evaluation of a lead-selective membrane electrode, containing lead diethyldithiocarbamate chelate, has also been described232. 

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