DETERMINATION OF SUBMICROGRAM AMOUNTS OF SILVER(I) BY QUENCHING OF FLUORESCENCE

The reaction of the bis-phenanthroline-silver(I) cationic complex with the counter-ion, 2,4,5,7-tetrabromofluorescein (eosin), to form the ternary complex, {[Ag(Phen)2+]2, TBF2-}, has been studied for the determination of submicrogram amounts of silver(I) ions in aqueous media. The eosin itself is fluorescent and in the presence of 1,10-phenanthroline, its sharpest excitation and emission peaks are at 300 and 545 nm, respectively. The addition of silver(I) ions to the eosin-phenanthroline solution causes a quenching of this fluorescence. With this method, silver(I) ions can be determined down to 4 p.p.b., with a reproducibility of 2.7%, in the pH range 3-8. Reaction is instantaneous and the fluorescence remains stable for two weeks. Twenty cations, including the other coinage and most of the other noble metals, and ten anions have been tested for their interferences in the presence of EDTA. Only palladium(II) and cyanides interfere seriously. © 1969.