Determination of Fe(II) and total iron in natural waters with 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine (PDT)

Abstract

A method for the determination of Fe(II) and total iron in natural waters using the chelating agent 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine (PDT) is reported. PDT is a ferroin-type ligand and forms a strongly coloured Fe(II) complex, whose concentration can be measured colourimetrically. PDT is the non-sulfonated precursor to Ferrozine (FZ), a commonly used reagent for Fe(II). Solvent extraction of the Fe(II)(PDT) 3 complex into 1,2-dichloroethane with the counter ion tetrabromophenolphthalein ethyl ester (TBPE) was found to be a most sensitive technique for measuring Fe(II) in natural waters using PDT. However, due to the rapid oxidation of Fe(II) in ambient seawater (pH 7.7–8.2) this method is better employed for measuring total iron, with the addition of a reducing agent. Attempts to pre-concentrate Fe(II) onto PDT loaded C18 Sep-Paks is hindered in seawater by the loss of PDT from the Sep-Pak. However, in low ionic strength solutions, PDT is retained on the Sep-Pak and quantitatively trapped Fe(II). This method can be utilised for measuring nanomolar concentrations of Fe(II) in lakes and rivers.