21. Solution to Chemistry Problem

3. Calculate the quantitative content of levomycetin stearate in the substance (SP X, pp. 389-390).
Method of determination. About 0.04 g (exact weight) of levomycetin stearate is dissolved in 95% ethanol in a 100 ml volumetric flask and the volume of the solution is brought to the mark with ethanol (solution A). 10 ml of solution A are transferred to a 100 ml volumetric flask and the volume of the solution is brought to the mark with ethanol (solution B).

The optical density of the resulting solution B is determined on a spectrophotometer at a wavelength of 272 nm in a cuvette with a layer thickness of 10 mm. In parallel, the optical density of a 0.002% solution of a standard sample of levomycetin stearate is measured at a wavelength of 275 nm.
The optical densities of the test and standard solutions are 0.360 and 0.400, respectively. The exact mass of the drug is 0.0369 g.