Bismuthiol II as an analytical reagent

Summary The estimation of bismuth by the reagent Bismuthiol II is studied critically. The effect of acidity, reagent concentration and interfering ions are given in detail. The maximum acidity that may be tolerated for the complete precipitation of bismuth is 0.3 N in nitric acid, 0.5 N in hydrochloric acid and 1N in sulphuric acid. Higher acidity than 0.1 N decomposes the reagent present in excess. In 0.1 N nitric acid bismuth has been separated from a number of ions like Al³⁺, Cr³⁺, Th⁴⁺, rare earths, Zr⁴⁺, Ti⁴⁺, UO₂²⁺, Be²⁺, Mn²⁺, Co²⁺, Ni²⁺, Mg, alkalis and alkaline earths, SO₄^2–, Cl^–, C₂O₄^2–- and from Fe²⁺ and Ce³⁺ in 0.1 N hydrochloric acid. In presence of a citrate or a tartrate it can be separated from As³⁺, Ce⁴⁺, MoO₄^2–- and WO₄^2–-at p_H 1.5 to 2.5. When Hg²⁺, Pb²⁺, Pd²⁺, Cd²⁺, Cu²⁺, Ag⁺ and Tl⁺ are present they are first precipitated by the reagent at p_H 6 to 8 in presence of a citrate or a tratrate and the bismuth is estimated gravimetrically in the acidified filtrate. Ions as F^– and PO₄^3– that form insoluble compounds with bismuth, Sb³⁺ and Sn²⁺ that form less soluble compounds with the reagent and Fe³⁺, VO₃^–, CrO₄^2–, AsO₄^3– that act as oxidising agents, interfere.