Simple coated-wire electrodes. prepared using an ordinan aluminum wire conductor covered with the plasticized poly(viny1 chloride) membrane. were used in potentiometric titrations of metal ions forming complexes with 1.10-phenanthroline and its derivatives. The method is based on the precipitation of ion pairs formed by metal phenanthroline complexes and tetraphenylborate. Titrations were accompanied with titration cun-es yielding v e n sharp potential breaks, so that ver). reproducible results could be taken even in titrations. of quite diluted solutions (down to 2.5 x 10-mol of the metal ion in the 25 cm3 of the sample titrated). Using the procedure described, the following cations were titratable in forms of their 1,lO-phenanthroline complexes: Zn". CdLi. Mn'-. Fez-, Fe'-, CoL-, Ni", Cu", VO"' , Ga3-. In'-. and TI'-. Some of the metal ion solutions, prepared from the salts of anal!.tical-reagent-gmde purin, can be recommended for use in standardization procedures of the sodium tetraphenylborate titrant. 2,9-Dimethyl-l ,lo-phenanthroline complexes of ZnL+, Cd'+. and Cu+ were also titrable. but the results were significantly erroneous. Metal 4,7-diphenyl-l,l 0-phenanthroline complexes were insoluble in water as well as in water/ethanol mixtures.
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