2. Calculate the content of phenobarbital in tablets according to the calibration graph, if 0.1495 g of the powder of crushed tablets was brought to the mark with ethanol in a volumetric flask with a capacity of 100.0 ml. 2.5 ml of the resulting solution was brought to the mark with 0.1 mol/l sodium hydroxide solution in a volumetric flask with a capacity of 200.0 ml. The optical density of the specified solution at a wavelength of 258 nm in a cuvette with a layer thickness of 10 mm relative to the solvent is 0.445.
To construct a calibration graph, 0.0500 g of phenobarbital, which meets the requirements of the PS, was dissolved and brought to the mark with ethanol in a 100.0 ml volumetric flask (solution A). In a volumetric flask with a capacity of 200.0 ml was made sequentially 1.0; 2.0;:..; 6.0 ml of solution A and made up to the mark with 0.1 mol/l sodium hydroxide solution in a 200.0 ml volumetric flask. The optical density of the obtained standard solutions under the same conditions is 0.176, respectively; 0.350; 0.539; 0.701; 0.891; 1.061. The mass of 20 tablets of phenobarbital is 3.0522 g.

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