Dispersive liquid-liquid micro extraction of uranium(VI) from groundwater and seawater samples and determination by inductively coupled plasma-optical emission spectrometry and flow injection-inductively coupled plasma mass spectrometry

A dispersive liquid-liquid microextraction (DLLME) method was developed for the determination of uranium(VI) in groundwater/seawater by inductively coupled plasma-optical emission spectrometry (ICP-OES) and flow injection-inductively coupled plasma mass spectrometry (FI-ICPMS). This is the first report on the extraction of uranium(VI) by a DLLME method. In this method, uranium(VI) was complexed with ammonium pyrrolidine dithiocarbamate (APDC) in the presence of cetyltrimethyl ammonium bromide (CTAB), which enhanced the hydrophobicity of the ion-association complex resulting in improved extraction into chloroform. The extraction was carried out after adjusting the pH of the water sample to 1. The uranyl ion was back extracted from chloroform layer with nitric acid for determination by ICP-OES/FI-ICPMS. Some effective parameters for complex formation and extraction, such as volume of extraction and disperser solvent, extraction time, pH and concentration of the chelating agent and surfactant have been optimized using ICP-OES. Under optimum conditions, enrichment factors of 11 and 25 were obtained from 10 mL of water sample for determinations by ICP-OES and FI-ICPMS respectively. The calibration graphs were linear in the range of 5-200 mu g L-1 and 50-5000 ng L-1 with limits of detection of 2.0 mu g L-1 and 30 ng L-1 respectively for ICP-OES and FI-ICPMS. The method has been applied to a few groundwater and seawater samples. The recoveries obtained for uranium(VI) in groundwater and seawater samples spiked to levels of 10 and 5 mu g L-1 were 90-105% respectively. The results obtained by the proposed method have been cross validated by laser fluorimetry.