FLAME ATOMIC ABSORPTION SPECTROMETRIC DETERMINATION OF TRACE AMOUNTS OF SILVER IN RADIOLOGICAL WASTE SAMPLES AFTER SOLID PHASE EXTRACTION USING MULTI-WALLED CARBON NANO-TUBES MODIFIED BY SODIUM DODECYL SULFATE

Abstract

Multi-walled carbon nano-tubes was modified with sodium dodecyl sulfate and used as a solid phase extraction adsorbent for the determination of trace silver in radiological waste samples by flame absorption spectrometry. The effects of pH, initial silver ion concentration, sample flow rate and volume, elution conditions and the amount of adsorbent on the recovery of the analyte were investigated and optimized. The results showed that silver could be fully adsorbed at pH 7.0 and eluted by 5.0 mL 2% thiourea in HNO3 (0.1 mol.L-1). Under the optimized conditions, the adsorption capacity of modified multi-walled carbon nano-tubes was found to be 3.2 mg.g-1 of silver. The detection limit of the proposed method was 350 μg. L-1 for silver with an enrichment factor of 35. The relative standard deviation for ten replicate measurement of 0.5 ug of silver from 700 mL samples was 4.7%. The analytical procedure was successfully applied to the determination of trace silver in a few radiological waste samples with the recoveries between 94% and 105%. Graphite furnace atomic absorption spectrometric technique was also used for the comparison with the suggested method for the determination of the real samples.