Ultrasonic-energy enhance the ionic liquid-based dual microextraction to preconcentrate the lead in ground and stored rain water samples as compared to conventional shaking method

Abstract

An efficient preconcentration technique based on ultrasonic-assisted ionic liquid-based dual microextraction (UA-ILDµE) method has been developed to preconcentrate the lead (Pb+2) in ground and stored rain water. In the current proposed method, Pb+2 was complexed with a chelating agent (dithizone), whereas an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) was used for extraction purpose. The ultrasonic irradiation and electrical shaking system were applied to enhance the dispersion and extraction of Pb+2 complex in aqueous samples. For second phase, dual microextraction (DµE phase), the enriched Pb+2 complex in ionic liquid, extracted back into the acidic aqueous solution and finally determined by flame atomic absorption spectrometry. Some major analytical parameters that influenced the extraction efficiency of developed method, such as pH, concentration of ligand, volume of ionic liquid and samples, time of shaking in thermostatic electrical shaker and ultrasonic bath, effect of back extracting HNO3 volume, matrix effect, centrifugation time and rate were optimized. At the sample volume of 25mL, the calculated preconcentration factor was 62.2. The limit of detection of proposed procedure for Pb+2 ions was found to be 0.54μgL−1. The validation of developed method was performed by the analysis of certified sample of water SRM 1643e and standard addition method in a real water sample. The extraction recovery of Pb+2 was enhanced≥2% with shaking time of 80s in ultrasonic bath as compared to used thermostatic electrical shaker, where for optimum recovery up to 10min was required. The developed procedure was successfully used for the enrichment of Pb+2 in ground and stored rain water (surface water) samples of an endemic region of Pakistan. The resulted data indicated that the ground water samples were highly contaminated with Pb+2, while some of the surface water samples were also have higher values of Pb+2 than permissible limit of WHO. The concentration of Pb+2 in surface and ground water samples was found in the range of 17.5–24.5 and 25.6–99.1μgL−1 respectively.