Supported-liquid membrane extraction as a selective sample preparation technique for monitoring uranium in complex matrix samples

A supported liquid membrane (SLM) extraction method is described for selective extraction of uranyl cation using tri-n-butyl phosphate (TBP) as an extractant and kerosene as a diluent. Sodium sulphate was used as the acceptor phase as well as the electrolyte solution in the final determination using adsorptive stripping voltammetry (AdSV) on a hanging mercury drop microelectrode (HMDE). The developed and optimised method was used for monitoring of uranium as a uranyl cation in environmental samples with complex matrices. Important parameters controlling the extraction process, viz. the pH of the donor and the acceptor phase and the concentration of the acceptor phase, were investigated. The specificity of sodium sulphate-uranyl complex formation in the acceptor determined the selectivity of the extraction process. The original sample input into the membrane showed high concentrations of other metals to be present, yet the concentration of these metals in the acceptor solution of the membrane was very low. The slow mass transfer of the extraction process was also investigated. The stripping of uranyl cation into the acceptor solution was found to be the limiting factor. The detection limit of the method was around 0.5 mug L-1 after extraction of a 30 mL sample volume for 60 minutes.