30. Solving a chemistry problem

195. When analyzing a 0.9816 g sample for cobalt content using the chemiluminescent photographic method, the glow of a sample of the analyzed solution, standards and a blank experiment was recorded on one plate. 0.5 ml of cobalt salt solution was placed in the cells of the cuvette, sodium salicylate was added (to eliminate the interfering effect of copper and iron cations) and the same amount of hydrogen peroxide. Then the cuvette was kept until the glow stopped completely; The plate was photometered using an MF-2 microphotometer. The ΔS value of standard solutions containing 4.0; 8.0; 12.0; 16.0 μg Co/ml, amounted to 0.17; 0.28; 0.40 and 0.53 respectively. Calculate the mass fraction (%) of Co in the sample if ΔSх = 0.20.