A novel poly(vinyl chloride) based membrane containing 5,10,15,20-tetrakis(2-furyl)-21,23-dithiaporphyrin (I) as an electroactive material along with sodiumtetraphenylborate (NaTPB), and nitrophenyl octyl ether (NPOE) in the ratio 10:100:1:150 (I:NPOE:NaTPB:PVC) (w/w) was used to fabricate a Mg(II)-selective sensor. The developed sensor exhibits a wide working concentration range of 9.2 x 10(-6)-1.0 x 10(-1) M, with a Nernstian slope of 30.0 +/- 1.0 mV/decade of activity and the response time of 15s. This sensor shows a detection limit of 8.0 x 10(-6) M. Its potential response remains unaffected of pH in the range 4.0-8.4, and the cell assembly can be successfully used in partially non-aqueous medium (up to 10% v/v) without any significant change in the slope or working concentration range. The sensor has a lifetime of about 8 weeks and exhibits excellent selectivity over a number of mono-, bi-, and trivalent cations including alkali, alkaline earth metal, heavy and transition metal ions. It has also been used for the determination of magnesium ion concentration in real samples. (C) 2011 Elsevier B.V. All rights reserved.