12. Titanium is a catalyst for the oxidation reaction of thiosulfate ion. The reaction rate is monitored by the change in the turbidity of the solution due to the resulting BaSO4 suspension (phototurbidimetric method). Achieving a constant turbidity corresponds to the optical density. Depending on the titanium concentration, the following data were obtained:
C(Ti), µg/dm3 1 3 5.5 7 10
t, since 2000 750 400 292 214
In the analyzed solution, an optical density of 0.25 was achieved under identical conditions after 345 s. Determine the concentration of titanium in the analyzed solution.

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