In this paper, dichloride 4,4',4'',4'''-tetra-tert-butylphthalocyanine cobalt (III) was synthesized and incorporated into a PVC membrane. The electrode prepared exhibits a selectivity sequence which is different from the classical Hofmeister pattern. The electrode has a high selectivity for nitrite and exhibits a linear response from 3×10^-^5 to 1×10^-^1mol.dm^-^3 of nitrite with a slope of -52mV/decade. The response mechanism of the electrode was studied using solvent extraction and UV-Vis spectroscopy by changing the axial coordination anions of the complex.

Key words: ULTRAVIOLET SPECTROPHOTOMETRY, REACTION MECHANISM, ION SELECTIVE ELECTRODE, MEMBRANE ELECTRODES, NITROUS ACID, COBALT PHTHALOCYANINE