SPECTROPHOTOMETRIC DETERMINATION OF IRON(II) IN SEAWATER AT NANOMOLAR CONCENTRATIONS

Natural Fe(II) concentrations in seawater have been determined by using the colorimeter reagent ferrozine [3-(2-pyridyl)-5,6-bis(4-phenylsulfonic acid)-1,2,4-triazine]. The ferrozine was adsorbed on a C18 Sep-Pak cartridge. Seawater samples ranging in volume from 50 to 400 ml were passed through the Sep-Pak with the Fe(II) being retained as the colored Fe(II)-ferrozine complex. The complex was extracted from the Sep-Pak column with 10 ml of methanol. Up to a 40-fold preconcentration of Fe(II) was possible using this method. The molar absorptivity of the Fe(II)-ferrozine complex in methanol was 28.1 x 10(3) l mol-1 cm-1 at 562 nm. The recovery of Fe(II) from the Sep-Pak was 91%. The detection limit for Fe(II) in seawater was 0.6 nmol l-1. The precision over the range 0.6-185 nmol l-1 was 2% or 0.2 nmol l-1, whichever is the larger. Copper(I) interference was minimized by complexing Cu(I) with neocuproine added to the methanol Sep-Pak effluent.