Direct atomization atomic absorption spectrometric determination of Be, Cr, Fe, Co, Ni, Cu, Cd, and Pb in water with zirconium hydroxide coprecipitation

Abstract

A method using direct graphite furnace atomization atomic absorption spectrometry combined with preconcentration by coprecipitation with Zr(OH)₄ has been developed for the determination of trace amounts of Be, Cr, Fe, Co, Ni, Cu, Cd, and Pb in natural water samples. Zirconium solution (5 cm³, 10 g dm^–3) was added to 100–1000 cm³ of the sample water and then the pH was adjusted to 9 using aqueous ammonia. The precipitate of Zr(OH)₄ containing the determinants was calcined at 600 °C in an electric furnace. A 1.0 mg portion of the precipitate was weighed in a tared miniature graphite cup and atomized in a graphite furnace according to an optimized heating programme. Calibration was effected using aqueous standard solutions. The results for three natural water samples were in good agreement with the values obtained using graphite furnace atomic absorption spectrometry for aqueous samples prepared by dissolution of the Zr(OH)₄ coprecipitates. The detection limits, which corresponded to twice the standard deviation for 20 measurements, were as follows (for 1000 cm³ of the sample solution): Be, 0.23 ng dm^–3; Cr, 1.4 ng dm^–3; Fe, 2.3 ng dm^–3; Co, 0.85 ng dm^–3; Ni, 0.88 ng dm^–3; Cu, 1.5 ng dm^–3; Cd, 0.38 ng dm^–3; and Pb, 0.42 ng dm^–3. The relative standard deviations (n= 5) were less than 10%.