Determination of Orange II and Sulfasalazine in Food, Tablets, Urine, Soil, and Water by In Situ Preparation of Nickel Hydroxide Nanoflakes/Magnetite Nanoparticles for Magnetic Solid-phase Extraction followed by Electrochemical Detection

Two new methods were developed for sub-nanomolar electrochemical detection of orange II and sulfasalazine. A hydrated Ni(OH)(2)/Fe3O4 phase was prepared in situ and used for enrichment of orange II and sulfasalazine. Thereafter, the nanosorbent phase was washed with the acidic solutions to release orange II and sulfasalazine before detection by adsorptive differential pulse voltammetry on a Pt electrode modified by carboxyl functionalized multi-walled carbon nanotubes and adsorptive square wave voltammetry on a glassy carbon electrode modified by freshly prepared gold nanoparticles/carboxyl functionalized multiwalled carbon nanotubes composite, respectively. The enrichment-detection methods provided limits of detection of 0.29 and 0.49 nmol L-1 for orange II and sulfasalazine, respectively. The linear working ranges for orange II and sulfasalazine were 0.5-10 and 5-80 nmol L-1. Also, the selectivity of the methods was investigated. No significant interferences were observed. The methods were successfully applied on the determination of orange II and sulfasalazine in food, tablets, urine, soil, and water samples. Furthermore, density functional theory was used to predict the most stable structures of the orange II and sulfasalazine complexes with the hydrated nickel hydroxide. In addition, experiments showed that the Sips isotherm was the most suitable for describing the adsorption of sulfasalazine by the nanosorbent.