Abstract: To avoid the use of highly toxic cyanide in the determination of total vitamin B₁₂ as specified in GB 5009.285—2022, the study mentioned by the title was proposed. The infant formula milk powder sample （5.000 0 g） was taken and placed in a 150 mL-conical flask with a stopper, and 30 mL of 0.25 mol·L⁻¹ sodium acetate buffer solution （pH 4.0）, 0.02 g of pepsin, and 0.02 g of amylase were added. The mixture was vortexed to homogenize, and subjected to enzymolysis with shaking at 37 ℃ for 30 min, then heated at 100 ℃ for 30 min. After cooling to room temperature, the pH of the solution was adjusted to approximately 7.0 with 0.1 mol·L⁻¹ sodium hydroxide solution. The solution was made its volume up to 100 mL with water. 40 mL of the solution was centrifuged for 10 min, and the supernatant was passed through a 0.45 μm glass fiber filter paper. 35 mL of the filtrate was passed through immunoaffinity column, with the flow rate controlled at 2 mL·min⁻¹. After the filtrate had completely passed through the column, the column was rinsed with 10 mL of water, vacuum-dried, and washed with 3 mL of methanol in 3 portions, and the eluate was collected and blown to near dryness by nitrogen at 60 ℃. 3 mL of the digestion reagent （the mixed solution of nitric acid and water at a volume ratio of 2∶1） was added, and the mixture was placed in a super microwave chemical platform. Digestion was carried out at a maximum digestion temperature of 220 ℃ for 10 min under the initial nitrogen pressure of 4 MPa. The digested solution was evaporated to 0.5 mL at 100 ℃ in order to remove acid, and made its volume up to 10 mL with water. Cobalt in the solution was determined by inductively coupled plasma mass spectrometry, with scandium used as the internal standard for online correction. The total amount of vitamin B₁₂ was indirectly calculated based on the stoichiometric relationship between cobalt and vitamin B₁₂. As shown by the results, linear relationship between the response intensities after internal standard correction and mass concentrations of cobalt was kept in the range of 0.100‒5.00 μg·L⁻¹, and lower limit of determination （10S/N） for vitamin B₁₂ was 1.0 μg·（100 g）⁻¹. Test for recovery was made by the standard addition method, giving results in the range of 94.4%‒106%, with RSDs （n=6） of the determined values less than 5.0%. The method was applied to the analysis of whole milk powder reference material, and the determined value of vitamin B₁₂ was within the certified range.