In situ determination of iron(II) in the anoxic zone of the central Baltic Sea using ferene as spectrophotometric reagent

Continuous flow analysis for soluble Fe(II) species in seawater was performed with a colorimetric method using ferene as a spectrophotometric reagent. The method is based on the measurement of absorbance of the [FeII(fer)3]4 --complex at 594 nm. No preconcentration-steps are required. Samples prepared in the laboratory in line with external calibration experiments have been successfully analyzed in the nanomolar range (R2 = 0.959). A detection limit of 20 nM was obtained. Furthermore, investigations were performed in situ with a wet chemical analyzer in the water column of the central Baltic Sea. Finally the results were consistent with measurements made by an independent laboratory based method (ICP-OES).