The potentiometric response characteristics (slope and selectivity) of
thiocyanate-selective electrodes based on Rh(III)tetraphenylporphyrins (TPP)
in dioctylphtalate plasticized poly(vinyl chloride) membranes with various
percentage (w/w) of components are compared.
The ionophore, rhodium(III)tetraphenylporphyrin chloride (ClRhTPP), was
synthesized according to the literature data1 and analyzed by his electronic
absorption spectra in the visible region, by IR and 1H-NMR spectra.
The effects of lipophilic cationic (trioctylmethylammonium chloride) and
anionic (sodium tetraphenyl borate) additives on the response characteristics
were investigated. The electrode shows a strong dependence of the sensitivity,
selectivity, detection limit and working range of the type and concentration of
additives.
Membrane electrodes with added lipophilic cationic sites exhibit reversible
and near-Nernstian response toward thiocyanate ions in the concentration
range of 10-1 – 10-5 M, with a good stability in time. The potentiometric selectivity
coefficients were determined according to the separate solution method and
shows better potentiometric selectivity fort thiocyanate over a number of common
anions (logKSCN, X): ClO−4 , -0,71; Sal-, -1,96; NO −3 , -2,87; NO−2 , -1,71; I-, -1,39; Cl-,
-3,71; F-, -3,80; Br-, -3,51.

1. A.K-S. Tse, B.M. Wu, C.W. Mak, K.S. Chan, J. Organomet. Chem., 1998,
568, 257-261