Novel ionic reverse mixed micelle supramolecules in dispersive liquid-liquid microextraction for the successive/individual sensitive speciation analysis of iron in natural water by UV–Vis spectrophotometry

Abstract

A sensitive UV–Vis spectrophotometry based procedure is delineated for ultra-trace speciation analysis of iron in natural waters. This study prepares and utilizes new ionic reverse mixed-micelles (i-RMMs) supramolecules for the coacervate microextraction of iron species successively or independently on field. The anionic dioctylsulfosuccinate-capric acid (DOSS-CA) and cationic Aliquat-336-capric acid (Aliquat-336-CA) RMMs are used as dispersing, ion-pairing and extractant, respectively for Fe(II) and Fe(III). In successive speciation, Fe(II) forms colourless Fe(II)-(phen)32+ at ng mL−1 level in weak acidic medium that reacts with anionic head groups of RMM and configurates as Fe(II)-(phen)32+-(DOSS-CA)2 ion-pair in inner hydrophilic core. This coloured ion-pair settles on the top as coacervate and leaves unreacted Fe(III) in bulk aqueous solution, which is extracted in the similar way as Fe(III)-(SCN)63−-(Aliquat-336-CA)3 ion-pair in strong acidic medium. The above strategy can be applied individually to Fe(III)/Fe(II). The iron species stabilized in coacervates are transported to laboratory for UV–Vis spectrophotometry detection. The pre-concentration and detection limits are 16 and 28; and 0.1 and 0.4 ng mL−1, respectively for Fe(II) and Fe(III). The recoveries are between 92 and 100% for both Fe(II) and Fe(III) at 100 ng mL−1. The accuracy is established by correlating the summation of discrete species concentration obtained with certified total iron of NIST CRMs 1643e and 1643f trace elements in water. This field oriented speciation is applied to real natural waters.