The GB/T 23273.7-2009 standard specifies a method for the determination of the amount of sulfate ions in cobalt oxalate, which is analyzed using the combustion-iodometry method. This method is suitable for the determination of the amount of sulfate ions in the range of 0.002% to 0.02%. The sample is first burned at high temperature in a muffle furnace at 500 ° C, followed by copper wire as a flux, oxygen is introduced in a combustion furnace at 1250 ° C to 1300 ° C, so that the sulfate analysis in the sample is sulfur dioxide. Sulfur dioxide is absorbed through the starch absorption solution and titrated with the iodine standard titration solution until light blue color appears as the end point. The standard also specifies the required reagents and instruments, including flux copper wire, standard sample, starch absorption solution, etc.