Abstract
Determination of yohimbine hydrochloride by amperometric titration was examined. Yohimbine hydrochloride undergoes quantitative reaction with silicotungstic acid in 0.1M potassium hydroxide solution to form a 2:1 complex and in hydrochloric acid to form a 4:1 complex. The reaction with phosphotungstic acid in hydrochloric acid gives a complex of 6:1 ratio, and these complexes separate out as a white precipitate. By the use of this reaction, a minute quantity of yohimbine hydrochloride was determined under following conditions: Ec=-0.75V (vs. S. C. E.) when silicotungstic acid was used as the titrant and Ec=-0.40V (vs. Hg pool) when phosphotungstic acid was used as the reagent. Mercury drop electrode was used. Concentration of hydrochloric acid must be over 0.05M when using silicotungstic acid and over 0.5M when using phosphotungstic acid.
