The separation of niobium from tantalum by extraction with tributyl phosphate and determination of niobium as the thiocyanate complex

A method is proposed for the rapid extraction and separation of microgram amounts of niobium(V). The niobium is extracted quantitatively by 100 % TBP from 7.7-9.4 M (initial) hydrochloric acid and determined spectrophotometrically as the thiocyanate in TBP-acetophenone solution. Beer's Law is obeyed at 430 mmu over the range 0.8-9.0 mug ml . The system is stable for 72 hr. Caesium, calcium, strontium, barium, aluminium, titanium(IV), zirconium(IV), cerium(TV), fluoride, thiocyanate and oxalate do not interfere (1 mg). Niobium(V) can be determined in a niobium(V)-tantalum(V) mixture. The method is accurate and reproducible to within +/-2%.