All-Solid-State CNT Composite Calcium(II)-Selective Potentiometric Sensor Based on 4,7-Diaza-2,3,8,9-Dibenzo-15-Crown-5 Ionophore

A composite of multi-walled Carbon nanotube (MWCN) and polyvinyl chloride (PVC) along with a synthesized neutral carrier 4,7-diaza-2,3,8,9-dibenzo-15-crown-5 (I) has been tried for its selective binding behavior for Ca(II) ions. Compound (I) works as an ionophore, exhibiting high selectivity for calcium ions, when taken with poly(vinyl chloride), sodium tetraphenylborate (NaTPB), MWCNT and  tris(2-ethylhexyl) phosphate (TEP) in the ratio 10:100:3:3:50 (w/w). This composition was used to fabricate a solid contact calcium(II)- selective potentiometric sensor. The developed all solid-state sensor worked well in the concentration range of 1.6×10-7-1.0×10-1 M, with a near Nernstian slope of 28.8+1.0 mV/decade of activity. The response time of this sensor was approximately 10 s. It exhibited a detection limit of 9.1×10-8 M. It worked satisfactorily in the pH range 3.5-7.0. The lifetime of the developed sensor was observed as six weeks and it exhibited good selectivity towards calcium ions over other cations.  It was successfully used as an indicator electrode in the potentiometric titration of Ca(II) with EDTA. It produced comparable results for the determination of the activity of calcium ions in real samples.