Novel PVC Membrane Based Alizarin Sensor and its application; Determination of Vanadium, Zirconium and Molybdenum

Abstract

A fabrication of new potentiometric alizarin sensor based on the use of alizarin Red-S-CTAB (ARS-CTAB) ion pair, in poly (vinyl chloride) (PVC) matrix, is reported. Effect of various plasticizers (o-NPOE, DBP, DEP, DOP, TBP, & CN) and cation excluder, Cetryltrimethylammoniumbromide (CTAB) was studied. The best performance was obtained with a membrane composition of PVC: o-NPOE: ARS-CTAB: CTAB ratio (w/w; %) of 31:60:7:2. The sensor exhibits significantly enhanced selectivity towards alizarin over the concentration range 1.0 × 10-8 to 1.0 × 10-3 M with a lower detection limit of 3.0 × 10-9 M and a Nernstian slope of 59.8 mV decade−1 of activity. Influence of the membrane composition, and possible interfering ions was investigated on the response properties of the electrode. Fast and stable response, good reproducibility and long-term stability are demonstrated. The sensor shows response time of < 10 s and can be used for about 3 months without any considerable divergence in their potential response. Selectivity coefficients determined with matched potential method (MPM) indicate high selectivity for alizarin. The proposed electrode shows fairly good discrimination of alizarin from anions. It was successfully applied to determination of vanadium ion in water and soil samples, zirconium ion in alloy samples and molybdenum ion in geological samples using indirect potensiometry and the results obtained are comparable with those provided by AAS analysis. The electrode can be used in the pH range of 2.0 to 5.0 and mixtures containing up to 20% (v/v) non-aqueous content. It was used as an indicator electrode in potentiometric titration of alizarin against EDTA.