ION CHROMATOGRAPHY OF ORGANIC-RICH NATURAL-WATERS FROM PEATLANDS .5. FE2+ AND FE3+

Pore waters from two peat bogs in the Jura mountains, Switzerland, were analyzed for Fe2+ and Fe3+ using ion chromatography (IC). In order to prevent oxidation, the samples were collected under N-2 using in situ diffusion-equilibrium pore water samplers (peepers). The metals were separated on a Dionex CS-5 analytical column and detected by visible absorbance at 520 nm after post-column mixing of the pyridine-2,6-dicarboxylic acid eluent with 4-(2-pyridylazo)resorcinol. The concentrations of total Fe determined by IC ranged from 0.1 to 2 mu g/g and agreed well with total Fe measured in the same samples with inductively coupled plasma spectroscopy. However, a problem is caused by humic substances present in the samples because they gradually contaminate the column. Contaminated columns show reduced precision, peak tailings and reduction of Fe3+ to Fe2+ on the column. The relatively high Fe3+ concentrations measured in the pore waters are not an oxidation artefact, but instead reflect the stabilization of the trivalent oxidation state by complexation with humic substances.