Determination of niobium(V) and tantalum(V) as 4-(2-pyridylazo)resorcinol-citrate ternary complexes in geological materials by ion-interaction reversed-phase high-performance liquid chromatography

A method for the simultaneous separation and determination of Nb(V) and Ta( V) as ternary complexes formed with 4-(2-pyridylazo)resorcinol (PAR) and ci trate was developed using ion-interaction reversed-phase high-performance l iquid chromatography on a C-18 column. Method parameters, such as pre-colum n complex formation conditions and composition of the complexes were invest igated using spectrophotometry and HPLC. Under the optimum conditions, the Nb(V) and Ta(V) complexes were eluted within 12 min with a mobile phase of methanol-water (32.68, v/v) containing 5 mM acetate, 5 mM TBABr and 5 mM ci trate buffer at pH 6.5, with detection at 540 nm. A typical separation effi ciency was 33 000 and 20 000 theoretical plates per metre for Nb(V) and Ta( V), respectively. The relative standard deviation of retention times for th e Nb(V) and Ta(V) complexes were 0.16% and 0.17% and for peak areas were 0. 28% and 1.36%, respectively. The detection limits (signal-to-noise ratio=3) for Nb(V) and Ta(V) were 0.4 ppb and 1.4 ppb, respectively. Results obtain ed for standard reference rock samples agreed well with certified values an d results obtained by inductively coupled plasma MS. (C) 1999 Elsevier Scie nce B.V. All rights reserved.