Pre-concentration of Trace Cobalt on Solvent-Soluble Membrane Filter Using Nitroso R and its Application for Graph i te Furnace Atomic Absorption Spectrometry

Abstract

A simple and highly effective pre-concentration method for a graphite furnace atomic absorption spectrometry of trace cobalt which involves the filtration of an ion pair of cobalt Nitroso R and a quarternary ammonium ion on an organic solvent soluble membrane filter followed by the redissolution using small volume of dimethylformamide is described. The optimum pre-concentration conditions were examined. The highest recovery was obtained by using benzyldimethyl (tetradecyl) ammonium for counter ion. The mechanism of the collection of the ion pair on the membrane filter was also discussed. The recommended procedure is as follows. To 1 dm' of sample containing 0-1 pg of cobalt(II), 1 cm3 of 0.02moldm-8 nitroso R solution and phosphate buffer, pH 8, are added, and after 3 min, 15 c m 3benzyldimethyl (tetradecyl) ammonium chloride solution is added. After 1 min, the solution is filtered by membrane filter (cellulose nitrate, diameter; 47 mm, pore size; 1 pm). The membrane filter is dissolved in 2 cm3 or 5 cm3 of DMF.20 mma of the solution is transfered to the graphite furnace of AAS and cobalt is determined at 2=-240.7 nm. The concentration factor (CF) was achieved 200-500. When CF was 200, RSD was 2.9%(n=5) and the sensitivity (=2 x SD) was 10 ppt and when CF was 500, RSD was 6.0% (n=5) and the sensitivity was 5 ppt. An application of the method for cobalt in river water was also descsribed.