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

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. (C) 2000 Elsevier Science B.V. All rights reserved.