A novel fiber optic spectrophotometric determination of nitrite using Safranin O and cloud point extraction

A novel fiber optic spectrophotometric method for nitrite determination in different samples is suggested, based on the reaction of nitrite with Safranin O in acidic medium to form a diazo-safranin, which is subsequently coupled with pyrogallol in alkaline medium to form a highly stable, red azo dye, followed by cloud point extraction (CPE) using a mixed micelle of a nonionic surfactant, Triton X-114, with an anionic surfactant, sodium dodecyl sulphate (SDS). The reaction and extraction conditions (e.g., acidity for diazotization and alkalinity for pyrogallol coupling, and other reagent concentrations, time, and tolerance to other ions) were optimized. Linearity was obeyed in a concentration range up to 230 μg L−1, and the detection limit of the method is 0.5 μg L−1 of nitrite ion. The molar absorptivity for nitrite of the Safranin–diazonium salt (ɛ610 nm = 4 × 103 L mol−1 cm−1) existing in literature was greatly enhanced by pyrogallol coupling and CPE enrichment (ɛ592 nm = 1.39 × 105 L mol−1 cm−1). The method was applied to the determination of nitrite in tap water, lake water and milk samples with an optimal preconcentration factor of 20.