Calcium(II)-selective potentiometric sensor based on p-isopropylcalix6arene in PVC matrix

Abstract

A new PVC-based membrane using p-isopropylcalix[6]arene (I) as an ionophore has been developed as a calcium-ion-selective sensor. Among various membranes prepared with and without plasticizer, the best performance was shown by a membrane with a composition (mg) I : NaTPB : PVC (2 : 2 : 120). This sensor exhibits a good potentiometric response to Ca²⁺ ion over a wide concentration range (3.9 × 10⁻⁶ to 1 × 10⁻¹ M) with a near Nernstian slope (30 mV per decade of activity) and response time of 15 s. The sensor can be used for a period of 3 months without any drift in potential. The selectivity coefficient values are in the order of 1.0 × 10⁻³ for mono-, bi-, and trivalent cations, which indicates a good selectivity for Ca²⁺ ion. The useful pH range for the electrode was found to be 2.5–6.0, and it works well in mixtures with non-aqueous content up to 25% (v/v). The sensor can also be used successfully as an indicator electrode in the potentiometric titration of Ca²⁺ against EDTA.

Keywords:

• Potentiometry
• Calixarenes
• Calcium
• Polyvinyl chloride
• Ion-selective sensor

Acknowledgement

One of the authors, JR, gratefully acknowledges Ministry of Human Resource Development (MHRD), India, for the support of this work.