Macrocycle Based Membrane Sensors for the Determination of Cobalt(II) Ions

Abstract

Poly(vinyl chloride) (PVC) based membranes of macrocycles, 5,7,7,12,14,14-hexamethyl-1,4,8,11- tetraazacyclotetradeca-4,11-diene diperchlorate (I), 3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclo- tetradeca-4,11-diene diperchlorate (II) and 5,10,15,20-tetraphenylporphyrin(III) with sodium tetraphenylborate (STB) as an anion excluder and dibutyl phthalate (DBP), dioctyl phthalate (DOP), dibutyl butylphosphonate (DBBP) and 1-chloronaphthalene (CN) as plasticizing solvent mediators were prepared and investigated as Co ^{2 +} -selective electrodes. The best performance was observed with the membrane having the composition III–PVC–STB–DBP in the ratio 3:8:1:8, which works well over a wide concentration range (8.0 × 10 ^{- 6} –1.0 × 10 ^{- 1} mol l ^-1 ) with a Nernstian slope of 29.0 mV per decade of activity between pH 2.8 and 7.3. This electrode shows a fast response time of 20 s and was used over a period of 4 months with good reproducibility (s = 0.4 mV). The selectivity coefficient values of the order of 0.01 for mono-, di- and trivalent cations indicate excellent selectivity for Co ^{2 +} over a large number of cations. Anions such as Cl ^- and SO ₄ ^{2 -} do not interfere and the electrode also works satisfactorily in a partially non-aqueous medium. The sensor has been used as an indicator electrode in the potentiometric titration of Co ^{2 +} with EDTA.