Pentacyclooctaaza as a neutral carrier in coated-wire ion-selective electrode for nickel(II)

1,3,7,9,13,15,19,21-Octaazapentacyclooctacosane (pentacyclooctaaza) have been explored as a neutral ionophore for preparing poly(vinyl chloride) (PVC)-based membrane sensors selective to Ni(II). The optimized membrane incorporating pentacyclooctaaza as the active material, dibutyl phthalate as plasticizer and sodium tetraphenyl borate as an anion excluder and membrane modifier in PVC (in the weight ratio of 5.5:56.5:5.5:32.5, respectively) was directly coated on the surface of a platinum-wire electrode. The electrode exhibited a near-Nernstian response in the concentration range of 1×10−6 to 1×10−1 M Ni(II). The limit of detection, as determined from intersection of the extrapolated linear segments of the calibration graph, was 6×10−7 M. It has a response time between 5 and 40 s for nickel concentrations ranging from 1×10−1 to 1×10−6 M. The electrode revealed moderate selectivities over a number of alkali, alkaline earth and several transition and heavy metal ions. The electrode is suitable for use in aqueous solutions in a wide pH range of 3–6. It was applied as an indicator electrode for the end point detection in the potentiometric titration of Ni(II) with ethylenediaminetetraacetic acid (EDTA) and determination of nickel content of chocolate and milk powder samples.