In a supporting electrolyte containing NH3/NH4Cl (pH 10.8) and NO2^-, a sensitive adsorptive complex wave of Co(Ⅱ)-α-furfuraldioxime was observed at -1.18 V (vs. SCE) by oscillopolarography, which has been successfully applied to the determination of trace Co(Ⅱ) in the injection of vitamin B12. The peak height is proportional to the concentration of Co(Ⅱ) (4×10^-10g·mL^-1-4×10^-8g·mL^-1) with detection limit of 2×10^-10 g·mL^-1. The properties of the polarographic wave were discussed by different electrochemical methods in...