Vortex-Assisted Modified Dispersive Liquid-Liquid Microextraction of Trace Levels of Cadmium in Surface Water and Groundwater Samples of Tharparkar, Pakistan, Optimized by Multivariate Technique.

A simple vortex-assisted modified dispersive liquid-liquid microextraction procedure is proposed for the enrichment of cadmium (Cd+2) in surface (stored rainwater) and groundwater of the Tharparkar district in Pakistan, before analysis by flame atomic absorption spectrometry. Ammonium pyrrolidinedithiocarbamate was used as a ligand to make a hydrophobic complex of Cd+2, which was extracted in an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate), and the nonionic surfactant Triton X-114 was applied as a dispersing medium. The contents of tubes were shaken for different time intervals on a vortex mixer to enhance extraction efficiency. A multivariate strategy was used to simultaneously evaluate seven factors including, concentration of the complexing reagent, pH, amounts of ionic liquid and Triton X-114, vortex shaking time, centrifugation time and extracting solution for their influence on the percentage recovery of the analyte. The important variables were further optimized by central composite design. The preconcentration factor and LOD were observed as 76.9 and 0.048 µg/L, respectively. The Certified Reference Material SRM1643e was used to check the validity of the developed method, and the RSD was found to be 4.02%. The proposed technique was successfully applied for the enrichment of Cd+2 in groundwater and surface water samples from the southeastern part of Pakistan. The observed results revealed that the concentration of Cd+2 in groundwater was higher than the World Health Organization recommended value of 3 µg/L for drinking water. For adults weighing approximately 60 kg, consumption of groundwater for drinking and other domestic purposes would provide levels of Cd+2 that are 2- to 3-fold higher than the provisional maximum tolerable daily intake.