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The N-(Antipyridynil)-N'-(2-methoxyphenyl) thiourea (NTU) was used as an excellent ionophore in the construction of a Co (II) PVC-based membrane sensor. This sensor illustrated very good selectivity and sensitivity towards cobalt ions over a wide variety of cations, including alkali, alkaline earth, transition and heavy metal ions. The sensor revealed a great enhancement in the selectivity coefficients for cobalt ions, in comparison with the formerly reported cobalt sensors. The developed sensor exhibited a Nernstian behavior (with a slope of 29.4+ 0.5 mV per decade) for a broad range (6.8 x10-7 1.0 x10-1 M) with a detection limit of 2.0 x10-7 M. It demonstrated a relatively fast response time in the whole concentration range (< 10 s) and its usage exceeded a 10 week period in the pH range of 2.7-8.3. The sensor applications were found to be successful in the direct determination of cobalt ions in wastewaters of industrial cobalt electroplating companies as well as an indicator electrode in the titration with EDTA.