Speciation and determination of iron using dispersive liquid–liquid microextraction based on solidification of organic drop followed by flame atomic absorption spectrometry

Abstract

A simple and efficient method for iron speciation (Fe²⁺, Fe³⁺) using dispersive liquid–liquid microextraction based on solidification of organic drop (DLLME-SFO) technique followed by flame atomic absorption spectrometry was developed. In this method, 1 mL of ethanol (as the disperser solvent) containing 50 µL of 1-undecanol (as the extracting solvent) was injected rapidly into the sample solution containing iron (II), iron (III) species and 1.1 × 10⁻³ mol L⁻¹ oxine (as the complexing agent). The procedure is based on the complexation of Fe³⁺ with 8-hydroxyquinoline (oxine) at pH 3, and extraction of the resulting complex using DLLME-SFO. The total Fe was determined after the oxidation of Fe²⁺ to Fe³⁺ with concentrated nitric acid. The concentration of Fe²⁺ was determined from the difference between the concentration of total Fe and the Fe³⁺. Some parameters such as pH, oxine concentration, ratio of disperser and extractant solvent were investigated. Under the optimum conditions, the calibration graph was linear in the range of 25–250 µg L⁻¹ for Fe³⁺ with a limit of detection (LOD) of 4.8 µg L⁻¹. The relative standard deviation (RSD, %) for 10 replicate determinations of Fe³⁺ at 50 µg L⁻¹ levels was 3.2%. To validate the developed method, a certified reference material (BRGM R52) was analysed and the determined value was in very good agreement with the certified value. The proposed method was successfully employed for determination of iron species in tap, well and spring water samples.

Keywords:

• dispersive liquid–liquid microextraction
• flame atomic absorption spectrometry
• iron speciation
• solidification of organic drop

Acknowledgement

The authors wish to thank the Ferdowsi University of Mashhad for the financial support of this project.