Combination of solid phase extraction and dispersive liquid–liquid microextraction for separation/preconcentration of ultra trace amounts of uranium prior to its fiber optic-linear array spectrophotometry determination

Abstract

A simple and sensitive method for the separation and preconcentration of the ultra trace amounts of uranium and its determination by spectrophotometry was developed. The method is based on the combination of solid phase extraction and dispersive liquid–liquid microextraction. Thus, by passing the sample through the basic alumina column, the uranyl ion and some cations are separated from the sample matrix. The retained uranyl ion along with the cations are eluted with 5mL of nitric acid (2molL−1) and after neutralization of the eluent, the extracted uranyl ion is converted to its anionic benzoate complex and is separated from other cations by extraction of its ion pair with malachite green into small volume of chloroform using dispersive liquid–liquid microextraction. The amount of uranium is then determined by the absorption measurement of the extracted ion pair at 621nm using flow injection spectrophotometry. Under the optimum conditions, with 500mL of the sample, a preconcentration factor of 1980, a detection limit of 40ngL−1, and a relative standard deviation of 4.1% (n=6) at 400ngL−1 were obtained. The method was successfully applied to the determination of uranium in mineral water, river water, well water, spring water and sea water samples.