SEPARATION AND DETERMINATION OF TRACE AMOUNTS OF VANADIUM(V), CHROMIUM(III) AND IRON(III) WITH 2-(2-THIENYLAZO)-5-DIETHYLAMINOPHENOL CHELATES BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

A reversed-phase high-performance liquid chromatographic method for the separation and the determination of vanadium(IV), chromium(III) and iron(III) with 2-(2-thienylazo)-5-diethylaminophenol chelates on a C18-bonded stationary phase by using methanol-tetrahydrofuran-water (20:15:65, v/v/v) containing 0.05 M lithium sulphate and 0.04 M acetate buffer (pH 5.5) as mobile phase and with spectrophotometric detection at 570 nm was developed. The method has high sensitivity, the detection limits being 0.5 ppb for vanadium(V), 2 ppb for chromium(III) and 1 ppb for iron(III). Under the optimum conditions, most other metal ions did not interfere, e.g., up to 1000-mu-g of magnesium(III), cadmium(II), zinc(II), lead(II), maganese(II), calcium(II), barium(II), tin(II, IV) and tungsten (VI), 400-mu-g of thorium(IV), 200-mu-g of iron(II), bismuth(III), zirconium(IV), 150-mu-g of gallium(III) and 120-mu-g of lanthanum(III) in the determination of 2.5-mu-g of iron(III) and chromium(III) and 1-mu-g of vanadium(V). The method can be applied to the simultaneous determination of trace amounts of vanadium(V), chromium(III) and iron(III) in water, tea leaves and rice samples.