Selective potentiometric determination of nitrite ion using a novel (4-sulphophenylazo-)1-naphthylamine membrane sensor

A novel polymeric membrane sensor sensitive to (4-sulphophenylazo-)1-naphthylamine (SPAN) based on the use of tris(bathophenanthroline) Ni(II)–SPAN ion pair as an ion exchanger in plasticised PVC membrane is described. The sensor exhibits a linear calibration plot with near-Nernstian anionic slope of −55.0±0.3 mV log[SPAN]⁻¹ over the concentration range 10⁻⁶–10⁻² mol l⁻¹ at pH 7. The sensor shows working range over the pH 6–8, response time of 20 s for 10⁻⁵ mol l⁻¹ and operational lifetime of 8 weeks. The sensor is used for quantification of micro quantities of nitrite ion by a prior conversion into the more lipophilic SPAN ion, which is measured with adequate sensitivity, and high selectivity using SPAN sensor. Validation of the method according to the quality assurance standards shows good performance characteristics. The sensor is satisfactory utilised for potentiometric determination of nitrite ion in wastewater samples and meat products. The results are favourably compared with data obtained using the standard spectrophotometric procedure involving the same reaction.