A new Zn(II)-selective potentiometric sensor based on 4-tert-butylcalix[4]arene in PVC matrix

Poly(vinyl chloride) (PVC) based membranes containing 4-tert-butylcalix[4]arene (I) as an electroactive material alongwith anion excluder sodiumtetraphenylborate (NaTPB) and plasticizer tri-butylphosphate (TBP) have been developed to fabricate a new zinc-selective sensor. Out of various compositions, the best performance was exhibited by the membrane having I, NaTPB, TBP and PVC in the ratio 8:5:100:200 (w/w). The sensor works well in the concentration range 9.8 × 10⁻⁶ to 1.0 × 10⁻¹ mol dm⁻³ with a near-Nernstian slope of 28.0 ± 1.0 mV/decade of activity. The detection limit is down to 5.0 × 10⁻⁷ mol dm⁻³. The working pH range of this sensor is 2.5–4.3 and it works well in partially non-aqueous medium up to 15% (v/v) (methanol, ethanol and acetone). It exhibits a fast response time of 30 s and could be used for more than four months without any considerable change in response characteristics. It has excellent selectivity for Zn(II) over other mono-, bi- and trivalent cations which have been reported to cause interference in the working of other sensors. It has been successfully used as an indicator electrode in the potentiometric titration of Zn(II) against EDTA and also to estimate zinc ions in industrial waste waters.