RADY
AND ERDEY* have use'd Thorin as an indicator in the EDTA titration: of bismuth, in nitric acid solution (PH 1-3). ,VANOSSID has mentioned that in aqueous perchloric or nitric acid .pedium a few micrograms of bismuth give a sensitive color reaction with. this reagent. However, an absorptiometric method for bismuth does not'appear to have been reported in the literature. In the present work conditions for such a determination are discussed, including the effect of many foreign species. ,:, EXPERIMENTAL A Spectronic zo spectrophotometer with cylindrical cells was used for absorptiol metric determinations.
,A stock solution o.05Oh in bismuth was prepared from A.R. grade Bi(NO& *5H20 in 0.x M perchloric acid. Its bismuth content was gravimetrically determined10 by weighing as oxide. Immediately before use this solution wasdiluted to 0.01 or 0.001% with water.
.Thorin (Baker Analyzed Reagent) was used without further purification as a 0.1% aqueous solution.
A.R. quality reagents were used through the work. Less common clement solutions were prepared from "Spec-pure" (Johnson Matthey & Co, London) metals, oxides or salts. ' PROCEDURE (A) For samples containing between 30-500 fig of bismuth. Transfer the nearly neutral or slightly acidic bismuth solution to a 2S-ml volumetric flask. Add the necessary volume of perchloric acid to provide a final acidity of 0.02-0.04 M and 2 ml of 0.1% Thorin solution, make up to volume with distilled water and measure the absorbance at ca. 535 m,u against a reagent blank solution as reference. Prepare a' standard curve from ,known amounts of bismuth following the same procedure. The sensitivity of this procedure is 0.022 pg Bi/cms for log IO/I equal to 0.001.