Aryl triazene derivative immobilized on agarose membrane for selective optical sensing and quantitation of Ni2+ in water

An aryl triazene (3-hydroxy-3-phenyl triaz-1-en-1-benzoic acid) was synthesized and first utilized as a highly selective ligand for the preparation of a novel optical sensor for nickel ion determination in aqueous solutions. The ligand was chemically bonded to a transparent agarose membrane after its epoxy activation for this purpose. Study of the complex formation between the ligand and some metal ions including Ni2+, Cu2+, UO22+, Cr3+, Fe3+, Mg2+, Co2+, Pb2+, Ca2+, and Ag+, in aqueous media, indicated a high selectivity towards Ni2+ and Cu2+ for it. After immobilization of the ligand on the agarose membrane, its selectivity for Ni2+ was substantially increased and a more distinct isosbestic point was observed. In addition, a sharp color change from yellow to green was detected upon contact with a solution of nickel ion at pH 9. The effects of pH, ligand concentration, response time, and interfering ions were carefully studied for the optical sensor. No significant interference from the above metal ions was observed. The absorbance of the membrane at 420 nm was linear for Ni2+ concentrations up to 9 × 10−4 mol L−1 with an R2 of 0.991. A detection limit of 2.74 × 10−6 mol L−1, repeatability of 2.2%, and reproducibility of 4.2% were obtained for the Ni2+ quantitation. The optical sensor was used for the analysis of nickel ion in some river water samples with satisfactory results.