2,2′:6′,2″-Terpyridine[hydroxypropyl-β-cyclodextrin] 1:3 complex used as chelating agent for the determination of iron with a sensitive, selective and fast liquid chromatographic method

In the present work, 2,2′:6′,2″-Terpyridine (terpy), a substance with very poor aqueous solubility, was dissolved in water, after formation of its inclusion complex with hydroxypropyl-β-cyclodextrin (HPβCD), in a 1:3 stoichiometry. The obtained [terpy:(HPβCD)₃] supramolecule, with enhanced aqueous solubility, enables its usage as a reagent at RP-LC methods. It was found that, terpy after inclusion complexation retains unaffected the ability of binding to Fe²⁺. It was also observed that, the stable, reddish-purple [Fe(terpy)]²⁺ complex was formed quantitatively in a wide pH range (2-9). Subsequently, iron as active substance or impurity in a drug product, can be determined through UV-vis measurements of [Fe(terpy)₂]²⁺. Speed, sensitivity and selectivity are the most important features of the isocratic RP-LC method, developed to determine iron in pharmaceutical formulations. The duration of the chromatographic separation was less than 4.0 min. The method was linear, precise and accurate from 0.17 to 2.2 mg l⁻¹ of iron and the detection limit was found to be 5 μg l⁻¹. The absorbance at 318 and 552 nm allowed the quantitation of Fe (II) and Fe (III) after reduction, as well as of total Fe (II + III). Moreover, there were no interferences from Fe³⁺, Ni²⁺, Co²⁺ or Cu²⁺.