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 HNO 3 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.
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