PVC-based neutral carrier and organic exchanger membranes as sensors for the determination of Ba2+ and Sr2+

Polyvinyl chloride (PVC) based membranes of dibenzo-24-crown-8(I) and 4-tert-butylcalix[8]arene (II) with and without plasticizers have been fabricated and explored as sensors for Ba2+ and Sr2+, respectively. The membrane incorporating the ingredients in the ratio 8:50:6:36 [I:PVC:NaTPB (sodium tetraphenylborate): CN (1-chloronaphthalene)] works well over the concentration range 1.4 x 10(-5)-1.0 x 10(-1) M of Ba2+ with a Nernstian slope of 30 +/- 1 mV per decade of concentration in the pH range 3.5-8.9 while the membranes of calixarene (11) were tried as Sr2+ selective sensors and it was observed that the membrane incorporating the ingredients in the ratio 9:50:5:36 {II:PVC:NaTPB: TEP [tris-(2-ethylhexyl) phosphoric acid]} showed the best response with a working concentration range of 2.0 x 10(-5)-1.0 x 10(-1) M and a near-Nernstian slope of 31.3 +/- 1.0 mV per decade of concentration in the pH range 2.4-4.8. Both sensors exhibit a fast response time of 15 s and work well in partially non-aqueous medium having up to 30% (v/v) alcohol content. The selectivity data showed that the electrodes are sufficiently selective over a number of interfering ions including alkaline earth metals. Anions like Cl-, NO3- also do not interfere in the functioning of the sensors. (C) 1999 Elsevier Science S.A. All rights reserved.