Abstract: In a slightly alkaline buffer solution of H3BO3-KCl-Na2CO3 at pH 8.7 (pH 8.6-9.2),a complex of mole ratio of 1 to 2 between divalent cobalt and salicylfluorone (SAF) was formed in the presence of CTMAB.The absorption maximum of the complex was found at the wavelength of 605 nm while the absorption maximum of the reagent blank was at 510 nm,thus giving a Δλ of 95 nm.The apparent molar absorptivity (ε605) of the colored complex was found to be 6.06×104L·mol-1·cm-1.Beer′s law was obeyed in the range of 0-5.5 μg of Co2+ per 25 mL of solution.Among the cations tested,Zn2+,Fe(Ⅲ) and Ni2+ were found to have serious interferences toward the determination of cobalt,but the interferences could be eliminated by adding sodium fluoride and thiourea.Besides,the co-existence of 3.2 times of Cu(Ⅱ) and 15 times of Pd(Ⅱ) did not interfere when 5 μg of Co2+ were determined.In the repeated analysis of a plating solution sample for 6 times,an average results of 0.103 g·L-1 with its RSD of 1.36% was obtained.Recoveries tested by standard addition method were in the range from 1012% to 104.8%.