98. Solving a chemistry problem

2. Determination of the specific indicator of chloramphenicol. Method of analysis: the exact mass of the drug (about 0.1 g) is placed in a 50 ml volumetric flask, 5 ml of ethanol is added and shaken, then 20 - 30 ml of water purified by heating are added, and adjusted to the mark with water (solution A). 1 ml of the resulting solution is transferred to a 100 ml volumetric flask, the volume of the solution is adjusted to the mark with purified water, and mixed (solution B). The optical density of solution B is measured at a wavelength of 278 nm, the reference solution is purified water. The specific absorption index value should be between 290 and 305.