Potentiometric ion‐pair titrations of metal ions forming complexes with 1,10‐phenanthroline and its derivatives

Abstract Simple coated‐wire electrodes, prepared using an ordinary aluminum wire conductor covered with the plasticized poly(vinyl chloride) membrane, were used in potentiometric titrations of metal ions forming complexes with 1,10‐phenanthroline and its derivatives. The method precipitation of ion pairs formed by metal phenanthroline complexes and tetraphenylborate. Titractions were accompanied with titration curves yielding very sharp potential breaks, so that very reproducible results could be taken even in titrations of quite diluted solutions (down to 2.5 × 10−7 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 1.10‐phenanthroline complexes: Zn2+, Cd2+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+, Vo2+, Ga3−, In3−, and Tl3−. Some of the metal ion solutions, prepared from the salts of analytical‐reagent‐grade purity, can be recommended for use in standardization procedures of the sodium tetraphenylborate titrant. 2.9‐Dimethyl‐1,10‐phenanthroline complexes of Zn2+, Cd2+, and Cu+ were also titrable, but the results were significantly erroneous. Metal 4,7‐diphenyl‐1,10‐phenathroline complexes were insoluble in water as well as in water/ethanol mixtures.