Studies on the adsorption of trace amounts of beryllium(II) on the surface of silica fibres from an aqueous phase for the development of a novel enrichment technique for electrothermal atomic absorption spectrometry

Abstract

Trace amounts of beryllium(II) were adsorbed on the surface of silica fibres from a weak alkaline solution. The distribution ratio depended on the pH of the solution; however, a constant value (log D= 5.1) was obtained at pH 9.5 in the concentration range 6.4–220 µmol kg^–1 in the silica phase. From the pH versus D curve, it was deduced that the beryllium(II) species adsorbed was (—SiO)Be(OH)₂^– or (–SiO)₂Be(OH)₂^2–. Based on these phenomena a simple enrichment technique was developed for the determination of trace amounts of beryllium(II) by electrothermal atomic absorption spectrometry. A 50–500 ml portion of the sample solution (pH 9.5) containing up to 6 ng of beryllium(II) was passed through a stack of three sheets of silica-fibre filter to collect the beryllium(II), which was then desorbed using three 0.5 ml portions of 0.5 mol l^–1 HCl containing 15 mg l^–1 of silicon for electrothermal atomic absorption spectrometry. A concentration factor of over 300 was easily attained. The detection limit, based on three times the standard deviation of the blank, was 0.15 ng of beryllium(II) for 500 ml of solution. The method was applied to the determination of beryllium(II) in natural water samples. A quantitative recovery was obtained when 3.0 or 6.0 ng of beryllium(II) were added to 500 ml of sea-water.