Ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate as a solvent for extraction of lead in environmental water samples with detection by graphite furnace atomic absorption spectrometry

A novel method is described for the preconcentration of ultratrace amounts of lead in water. Dithizone is employed as a chelator forming a neutral lead-dithizone complex to extract lead ions from aqueous solution into the ionic liquid 1-octyl-3- methylimidazolium hexafluorophosphate. Under optimal conditions, the extraction efficiency in one step and back-extraction efficiency with 5 mL of 0.1 mol L-1 nitric acid were 99.9 and 99.8% for 20 mu g of lead in 1 L of water solution, respectively. Preconcentration coupled with graphite furnace atomic absorption spectrometry was developed for the determination of lead in environmental water samples. The calibration graph was linear with a correlation coefficient of 0.998 at levels near the detection limits up to at least 0.1 mu g L-1. The detection limit, calculated as three times the standard error of the estimated calibration graph, is 1.0 ng of lead per liter of water sample. The determination of lead was free from interference from almost all cations and anions, and from humic acid in water from plant rot. Lead recoveries between 97.8 and 100.8% for spiked samples prove the accuracy of the method.