A new low-level HPLC technique for quantitative determination of niobium in rocks

Abstract

A high-performance liquid chromatographic (HPLC) technique for Nb is presented and has been applied to the accurate determination of Nb in rock samples with concentrations as low as 0.3 ppm. A detailed description of the analytical method is presented. Samples of 40-250 mg are acid-digested using HF HNO3 and HCl in screw-cap Savillex® beakers and the Nb separated from matrix elements by an efficient and quantitative mixed-acid separation scheme utilizing anion-exchange resin. Prior to the HPLC analysis, the isolated Nb is complexed with the organic ligand PAR (4-(2-pyridylazo)resorcinol), leading to the formation of a strongly colored complex. The Nb determination is then carried out utilizing reversed-phase HPLC with spectrophotometric detection of the Nb-PAR chelate. Data for 10 international standard rocks (e.g., BHVO-1, W-1, W-2, BIR-1, MRG-1, JA-2, JB-3) have been collected and show excellent agreement compared to values obtained by spark-source mass spectrometry and inductively coupled plasma-mass spectrometry. The 2σ external precision of the Nb analyses is ∼ ±5% throughout the entire concentration range of 0.3-100 ppm studied. © 1994.