1-(6-choloroquinoxaline-2-yl) Hydrazine as an Excellent Ionophore for Ppreparation of a Cobalt Selective Electrode and Potentiometric Measuring of Vitamin B12 in Pharmaceutical Samples

In this study, a potentiometric cobalt selective membrane sensor was prepared based on 1-(6-choloroquinoxaline-2-yl) hydrazine as a new ionophore. At first, the lowest-energy conformer of 1-(6-choloroquinoxaline-2-yl) hydrazine molecule (Ligand) and four local structure minima corresponding to their complexes with various ions were obtained using density functional theory (DFT). The calculated results of the Gibbs free energy of the reaction at B3LYP/6-31G(d) level show that the thermodynamic reactivity of complexation of cobalt ion (Co2+) with studied ligand is the best. Finally, a liquid membrane electrode for potentiometric monitoring of ultra-trace amounts of Co2+ was prepared by using this ligand. The electrode exhibits a Nernstian response for Co2+ ion over a wide concentration range of 1.0×10-1 to 3.0×10-6 mol L-1. The limit of detection of the sensor is 1.0×10-6 mol L-1. The sensor has a relatively fast response time (~10 s) and a useful working pH range of 3.0-8.0. Interferences of some cations were also evaluated. It was used as an indicator electrode in potentiometric titration of Co2+ with EDTA and in indirect determination of vitamin B12 in pharmaceutical samples. The results indicate that this electrode is sensitive for determination of Co2+ and vitamin B12.