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To distinguish between Fe(II) and Fe(III) species in atmospheric water samples, we have adapted an analytical procedure based on the formation of a specific complex between Fe(II) and ferrozine (FZ) on a chromatographic column. After elution of Fe(III), the Fe(II) complex is recovered with water-methanol (4:1). The possibility of trace iron measurements in this complex medium by graphite-furnace atomic-absorption spectrometry has been investigated. A simplex optimization routine was required to complete the development of the analytical method.

A quasi-on-line method of measurement of the oxidation states of iron coupled with a GFAAS analysis is reported for the trace conditions found in atmospheric waters. This technique is based on the formation of a specific complex [Fe(FZ) 3 ] 4À between Fe(II) and ferrozine (FZ). tC 18 solid-phase extraction cartridges (Sep-Pak) are used to separate the [Fe(FZ) 3 ] 4À and Fe(III) so as to limit the risk of redox evolution of the sample. The adaptation to dilute aqueous media, via acidification at pH ¼ 2 of rainwater sample, and atmospheric interferences are discussed, and the Fe(II) recovery in rainwaters is determined. This method coupled with a quasi-on-line sampling protocol has been tested on rains collected in Guadeloupe Island (Caribbean Sea, 16 N, 61 W) during a field campaign in May 2005. Our results show that the proposed method can satisfactorily be applied to the determination of Fe(II) and Fe(III) in atmospheric waters under in situ conditions.

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