High sensitive optode for selective determination of Ni2+ based on the covalently immobilized thionine in agarose membrane

A novel Ni2+ optode was prepared by covalent immobilization of thionine, 3,7-diamine-5-phenothiazoniom thionineacetate, in a transparent agarose membrane. Influences of various experimental parameters on Ni2+ sensing, including the reaction time, the solution pH and the concentration of reagents were investigated. Under the optimized conditions, a linear response was obtained for Ni2+ concentrations ranging from 1.00 × 10−10 to 1.00 × 10−7 mol l−1 with an R2 value of 0.9985. The detection limit (3σ) of the method for Ni2+ was 9.30 × 10−11 mol l−1. The influence of several potentially interfering ions such as Ag+, Hg2+, Cd2+, Zn2+, Pb2+, Cu2+, Mn2+, Co3+, Cr3+, Al3+ and Fe3+ on the determination of Ni2+ was studied and no significant interference was observed. The membrane showed a good durability and short response time with no evidence of reagent leaching. The membrane was successfully applied for the determination of Ni2+ in environmental water samples.