Bismuth European Pharmacopoeia

The test identifies the substance to be examined as a salt of bismuth, Several insoluble bismutii salts have foxmd use orally as antacids and topically in the treatment of skin disorders. Others have been used in the treatment of syphilis and as an amoebicide. Most of these therapeutic substances have been replaced by more modem alternatives, and reference to bismuth is currently made in only four monographs, and just one dictate method (a). Bismuth forms trivalent and pentavalent ions, but the trivalent is by far the most conunon. Most bismutii(III) and bismuth(V) forms insoluble salts, especially xmder alkaline conditions. This behavior and the insolubility of bismuth sulphide form the basis of test (a). In test (b) a colored complex between bismuth and thiourea is formed. 

5 mg of the substance to be examined add 10 ml of dilute hydrochloric acid R or use 10 ml of the prescribed solution. Heat to boiling for 1 min. Cool and filter if necessary. This procedure should bring the most likely otherwise insoluble bismuth salt into solution. In the next step of analysis, 1 ml of the solution obtained is added to 20 ml of water R, upon which a white or slightly yellow precipitate is formed. Bismuth(lll) hydrolyzes water, forming the bismuthyl ion. 

This ion forms an insoluble salt with most anions. In the case of a diluted hydrochloric acid solution, the precipitate will predominantly be with chloride, but in the case of other anions a mix of salts could be present BiOCl, (010)2804, and Bi(0H)2N03. 

Finally, 0.05 ml to 0.1 ml of sodium sulphide solution R is added, upon which the precipitate should turn brown, owing to the formation of bismuth sulfide. 

8ince bismuth sulfide is the only brown sulfide, a high degree of selectivity is obtained, although several cations are soluble in hydrochloric acid and precipitate upon dilution with water. The exact color of the various sulfide salts is the subject of some debate, though. Some references claim that bismuth sulfide is black, and some state that tin(II) sulfide is brown.  

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This test identifies the substance to be examined as a salt of antimony(III), Sb +, or antimony(V), Sb +. Antimony(III) and antimony(V) were formerly used in the oral treatment of intestinal worms and topically in the treatment of infections of protozoan parasites in the skin. But since especially tetrava-lent antimony is poisonous, they have generally been replaced by less toxic alternatives. At present, there are no monographs of antimony compounds in the European Pharmacopoeia. Antimony forms both tetra- and pentavalent ions, but the pentavalent is mainly found in oxides containing the antimonate ion, Sb04. Antimony(III), on the other hand, can be found as the free dissociated ion, Sb +, but, as also for example bismuth, since it reacts with water at neutral pH, forming antimonate. 

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