Experimental determination of Fe isotope effect for reduction from Fe(III) to Fe(II)

<p>All of the experiments described here begin with Fe(III) bound to the organic ligand ethylenediaminetetraacetic acid (EDTA), and proceed as Fe is reduced to Fe(II). The Fe(II)-specific ligand ferrozine (FZ) is added to the experimental solution in order to capture Fe(II) produced during the experiment, similar to methods previously used to capture Fe(II) produced during biological reduction of Fe(III) (Shaked et al., 2004). Fe(II) in the presence of ferrozine forms an Fe(II)FZ3 complex. This complex has a strong purple color, which made it possible to determine reaction extent visually and by absorbance spectrophotometry. The Fe(II)FZ3 complex is also hydrophobic, allowing us to separate it from the solution by passing the solution through a C18 resin (Waters Sep-Pak C18 Plus Light) with a peristaltic pump. The column was then rinsed with 5 mL of seawater and Fe(II)FZ3 was eluted with 5 mL methanol.</p>