AN IMPROVED METHOD OF POLAROGRAFHIC ESTIMATION OF RIBOFLAVIN

Riboflavin is very sparingly soluble in water but much more soluble in acid and alkaline solvents.The acid solution of riboflavin shows,however,an ano- malous forewave in polarogram,while the alkaline solution undergoes photolytic decomposition.For these reasons,the polarographic determinations of riboflavin found in literature have been conducted in buffer solution alone or by adding some other chemicals in order to increase its solubility.The authors made nu- merous experiments on revision of the conditions and found that riboflavin,once dissolved in dilute alkaline solution,would not precipitate out by neutralizing with hydrochloric acid and that the alkaline solution before neutralization did not show photolysis within three hours.Based upon this facts,a simplified method is pro- posed below. Dissolve about 5 mg of riboflavin in 25 ml of 0.01N potassium hydroxide, then neutralize with 0.1N hydrochloric acid.Add 10 ml.of 1N potassium chlo- ride and sufficient distilled water to make 100 ml.Place an aliquot of this solution in polarographic cell,pass hydrogen gas for 10 minutes to remove the dissolved o- xygen in solution,and then determine polarographically.This method can also be applied for assaying riboflavin tablets directly.