Extraction-spectrophotometric determination of niobium with 1,2,4,6-tetraphenylpyridinium perchlorate and thiocyanate

Abstract

1,2,4,6-Tetraphenylpyridinium (TPP⁺) as the acetate or perchlorate was used as a counter ion in the spectrophotometric determination of Nb(V) by extraction into toluene of the anionic Nb(V)-thiocyanate complex from 4–6 M hydrochloric acid. The molar absorptivity of the ion-association complex, whose composition was shown to be NbOCI(SCN)₃^–. TPP⁺, was 2.82 × 10⁴ l mol^–1 cm^–1 at 395 nm. Beer's law was obeyed over the range 0.1–2.5 µg ml^–1 of Nb(V). The method was applied to the determination of niobium in standard steels and ores (culombite type) with good precision and accuracy.

1-(4′-Nitrophenyl)-2,4,6-triphenylpyridinium (nitro-TPP⁺) perchlorate was also synthesised and used in the spectrophotometric determination of Nb(V), but did not show advantages over TPP⁺. The fluorescence of TPP⁺ and Nb(V)-SCN^–-TPP⁺ solutions in toluene also disappeared when nitro-TPP⁺ was used, owing to the paramagnetic effect of the NO₂ group.