Cloud point extraction for speciation of iron in beer samples by spectrophotometry

A new method based on the cloud point extraction (CPE) separation and spectrophotometric detection was proposed for the determination of iron species. In this method, Fe(II) reacts with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) in the presence of EDTA yielding a hydrophobic complex, which then is extracted into surfactant-rich phase. Total iron was determined after the reduction of Fe(III) to Fe(II) by using ascorbic acid as reducing agent. Variable parameters affecting the CPE efficiency were evaluated and optimised. The calibration graph was linear in the range of 5.0–112 μg/L (at 742 nm) for both species. Under the optimised conditions, the detection limits of 0.8 μg/L and 1.0 μg/L and the relative standard deviations of 2.0% and 2.6% (C_Fe(II) = C_Fe(III) = 10 μg/L, n = 5) for Fe(II) and Fe(III) were found, respectively. The proposed method has been applied to the speciation of iron in beer samples with satisfactory results.