A series of polymeric nitrite-selective electrodes containing a new lipophilic ionophore Co(II) tert-butyl-salophen is reported. The stability of Co(II) ionophores within a PVC-based membrane was investigated by leaching experiments. Different membrane compositions were explored in order to reach the lowest possible limit of detection for a PVC-based nitrite selective polymeric membrane electrode containing this ionophore. The optimal electrode showed a limit of detection of 2×10−6 M and exhibited four orders of magnitude of discrimination over nitrate, chloride and bromide. The electrodes were evaluated in undiluted human urine and attest to the robustness of the ionophore.