Bismuthiol II as an analytical reagent

Summary

The reagent Bismuthiol II completely precipitates palladium at a maximum acidity of 0.3 N in nitric acid, 0.5 N in hydrochloric acid or 1 N in sulphuric acid and also at a maximum p_H of about 8.0. The palladium complex Pd (C₈H₅N₂S₃)₂ is stable even up to a temperature of about 250° C. From a mineral acid solution palladium can be estimated in presence of ions of Fe²⁺, Al, Cr, Th, Ce³⁺, Zr, Ti⁴⁺, UO₂ ²⁺, Be, Mn, Co, Ni, Mg, P0₄ ³⁻, AsO₄ ³⁻, rare earths, alkalis, alkaline earths, Ce⁴⁺, WO₄ ²⁻ and MoO₄ ²⁻ that are not ordinarily precipitated by the reagent. At a p_H of 4.75 to 8.2, EDTA, Na-salt, keeps in solution, besides the above ions, the ions of Tl+, Cu²⁺, Pb, Bi³⁺, As³⁺, Sb³⁺, Zn, Cd, Fe³⁺, CrO₄ ²⁻, AsO₃ ³⁻ and VO₃ ⁻. Tartrate, however, at a p_H 6.2–8, keeps all the ions including Sn⁴⁺ in solution except of course Tl⁺, Cu²⁺, Pb and Cd. Separation from Ce⁴⁺, WO₄ ²⁻, MoO₄ ²⁻ and AsO₄ ³⁻ at a low p_H require the presence of tartrate. Ag⁺, Hg²⁺ and also Pb may be complexed with potassium iodide at a p_H 6–8. Tl⁺ and Ag⁺ may also be separated in presence of cyanide in an acetate buffer when palladium remains in solution and from which it may be re-precipitated by acidification.