Evaluation of mercury concentrations in groundwater samples of coal field using a matrix-less cloud point extraction procedure prior to analysis by cold vapor atomic absorption spectrometry

A novel matrix-less cloud point extraction (ML-CPE) procedure was developed for the determination of mercury (Hg) in groundwater samples collected from the Thar coalfield, Pakistan. For preconcentration of Hg, a complexing reagent, diethyl-dithiophosphate (DEDTP) was selected. Various parameters such as temperature, time, pH, and amount of complexing reagent and concentration of surfactant concentrations were studied in order to find the best conditions for the enrichment of mercury in water samples. In the proposed method, the Hg-DEDTP was subsequently entrapped in the nonionic surfactant, Triton X-114. Then, Hg was back-extracted into the matrix-less aqueous phase and determined by cold vapor atomic absorption spectrometry (CVAAS). At opti mized experimental parameters, the limit of detection and the enhancement factor were found to be 7.5 ng/L and 22.8 ng/L, respectively. The relative standard deviation (RSD) for six replicates at 5 μg/L of Hg was 4.6%, which indicates that the developed method is highly precise and repeatable. The accuracy of the method was verified by spiking the known concentration of the standards in a real sample. No significant difference (p > 0.05) was observed between the experimental results and the added analyte. The developed ML-CPE method was successfully applied for the preconcentration and determination of Hg in groundwater samples. The levels of Hg in the groundwater samples of the Thar coal field was in the range of 1.8-3.23 μg/L.