A specific spectrofluorimetric determination of terbium as its EDTA-sulphosalicylic acid complex

Abstract

The ternary complex formed by terbium with ethylenediaminetetra-acetic acid and sulphosalicylic acid has been used as the basis of a spectrofluorimetric determination of between 6·4 × 10^–3 and 3·2 µg of terbium per ml. The system absorbs radiation characteristic of sulphosalicylic acid (about 320 mµ) and emits the band fluorescence of sulphosalicylic acid (410 mµ), together with the sharp line emission characteristic of terbium (III)(545 mµ). The determination is carried out with 4 × 10^–3M EDTA and 2 × 10^–3M sulphosalicylic acid in aqueous solution at a pH of between 11·6 and 11·9. No interference resulted from 50-fold molar excesses of the other rare earth ions, 33 other metal ions or 14 anions. The fluorescence was not subject to oxygen quenching, was stable for several days and had a temperature coefficient of –0·87 per cent. per °C. Analytical results obtained with prepared samples have been included.