A highly selective optical sensor for catalytic determination of ultra-trace amounts of nitrite in water and foods based on brilliant cresyl blue as a sensing reagent

A new optical sensor has been developed for nitrite determination based on the use of brilliant cresyl blue (BCB) immobilized on triacetyl cellulose membrane using absorption spectrophotometry. The sensor is based on the reaction of BCB with bromate as an oxidant in the presence of nitrite in acidic media to produce a colorless product. Nitrite has a strong catalytic effect on the reaction of BCB with bromate. The difference in the absorbance of the optode at 570 nm between uncatalyzed and catalyzed reactions (ΔA) was found to be directly proportional to the concentration of nitrite. A detection limit was found to be 1.76 nmol L−1 (0.08 ng mL−1). The corresponding detection limit of 1.9 nmol L−1 is well below the maximum admissible concentration level of 2.2 μmol L−1 required by the European Community. The sensor response from different probes (n = 8) gave an RSD% of 2.4% at 2.17 μmol L−1 nitrite concentration. The proposed sensor was successfully applied for the determination of nitrite in water and food samples.