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Novel method for in-situ surfactant-based solid-phase extraction: application to the determination of Co(II) and Ni(II) in aqueous samples
Authors:Seyed Reza Yousefi  Farzaneh Shemirani
Institution:1. Waste Management Department, NFCRS, Nuclear Science and Technology Research Institute, P.O.BOX?11365/8486, Tehran, Iran
2. School of Chemistry, University College of Science, University of Tehran, Tehran, Iran
Abstract:We report on a completely new kind of solid phase extraction which we term in-situ surfactant-based solid-phase extraction (ISS-SPE). It represents a simple and rapid method for extraction from aqueous samples and preconcentration of compounds containing hydrophobic (alkyl) groups. A cationic surfactant containing alkyl chain is dissolved in the aqueous sample. Following the addition of hexafluorophosphate (HFP; an ion-pairing anion), solutions turn cloudy due to the interaction between the surfactant and the HFP ion. This is due to the formation of fine solid particles composed of the HFP salt of the cationic surfactant. The alkyl groups of the surfactant in the solid particles strongly interact with hydrophobic groups of analytes and become bound. The solid particles are centrifuged, and the sedimented particles can be either dissolved in an appropriate organic solvent, or leached with a solvent to recover the absorbed analyte(s). The method presented here has distinct advantages in that the extraction times are short and recoveries are high, probably a result of the formation of very fine particles of large specific surface, and of their good dispersion in the sample solution. The performance of ISS-SPE was demonstrated by extracting chelates of Co(II) and Ni(II) from water samples. Under the optimized conditions, the preconcentration factors are 51 and 45, respectively, and the detection limits are 0.9 and 0.6???g?L?1. The method was validated by the analysis of a certified reference material and by comparing results with those obtained by electrothermal AAS.
Figure
In ISS-SPE method, a cationic surfactant containing alkyl chain is dissolved in aqueous sample. After addition of hexafluorophosphate anion, a cloudy solution is formed due to formation of fine solid particles (surfactant hexafluorophosphate salt). Hydrophobic anaytes can be adsorbed on the alkyl group of the solid particles and extracted.
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