Green speciation of iron using aqueous two-phase system

Abstract Fe(II) and Fe(III) have distinct chemical and biological functions. Consequently, it is more important to determine the fraction of both oxidation state that knowing the total iron concentration in a sample. However, green methods for iron speciation are still limited. This work uses aqueous two-phase system, a safe alternative to liquid–liquid extraction, to perform the chemical speciation of iron. This method is based on the reaction of Fe(II) with 1,10-phenanthroline extractant, forming a complex of Fe(II)-phenanthroline that concentrates in the top phase of the system. The Fe(III) specie concentrated in the bottom phase of the system. Iron speciation was affected by the electrolyte nature, macromolecule type, quantity of phenanthroline added, and pH. The system formed by PEO1500 + Na3C6H5O7 + H2O at pH 6.00, containing 5.00 mmol kg-1 of phenanthroline, was successfully used to separate the iron species before determination by flame atomic absorption spectrometry. Under these optimal conditions, a separation factor of 233 was obtained between Fe(II) and Fe(III) with extraction percentages of (95.1 ± 1.0)% and (7.68 ± 0.50)%, respectively The proposed method was successfully applied for iron speciation in water samples, and provided recovery percentages ranging between 90 and 106%.

摘要：二价铁（Fe(II)）与三价铁（Fe(III)）具有截然不同的化学与生物学功能。因此，相较于测定样品中的总铁浓度，分别确定两种氧化态铁的占比更为重要。然而，用于铁形态分析的绿色分析方法仍较为匮乏。本研究采用水相双相体系——一种安全的液液萃取（liquid–liquid extraction）替代方案——开展铁的化学形态分析。该方法基于二价铁与1,10-邻菲啰啉（1,10-phenanthroline）萃取剂的配位反应，生成二价铁-邻菲啰啉络合物，该络合物富集于体系的上相；而三价铁物种则富集于体系的下相。铁的形态分析效果受电解质种类、大分子类型、添加的邻菲啰啉用量以及pH值的影响。以PEO1500 + Na3C6H5O7 + H₂O构建的体系，在pH 6.00、邻菲啰啉添加量为5.00 mmol·kg⁻¹的条件下，成功实现了铁物种的分离，随后可通过火焰原子吸收光谱法（flame atomic absorption spectrometry）进行定量检测。在该最优条件下，二价铁与三价铁之间的分离因子可达233，二者的萃取率分别为(95.1 ± 1.0)%与(7.68 ± 0.50)%。本方法已成功应用于水样中的铁形态分析，加标回收率介于90%~106%之间。