ION CHROMATOGRAPHY OF ORGANIC-RICH NATURAL-WATERS FROM PEATLANDS .3. IMPROVEMENTS FOR MEASURING ANIONS AND CATIONS

Organic-rich, anaerobic pore waters from peatlands have been sampled using peepers which filter the waters in situ. Pore waters collected using these devices are neither oxidized nor degassed. Anions (F-, acetate, formate, Cl-, HCO3-, NO2-, Br-, NO3-, PO43-, SO42- and S2O32-) and cations (Na+, K+, Mg2+ and Ca2+) were analyzed using ion chromatography (IC). With a Na berate gradient increasing from 4.9 to 24.5 mM, F-, acetate, formate, Cl-, HCO3-, NO3-, PO43- and SO42- can be quantified in one run (12 min). The high concentrations of dissolved CO2 in the pore waters are manifested as a broad HCO3- peak in the chromatograms. This allows HCO3- to be quantified (with a linear calibration curve from 40 to 800 mu g/g), but interferes with the Br- and NO2- peaks. Measurement of these two species requires sample degassing to remove dissolved CO2. While S2O32- can also be determined using a modified berate gradient (7 to 35 mM), its concentration in the pore water samples is below the detection limit of approximately 30 ng/g. In an earlier report, IC measurements of Na+, K+, Mg2+, and Ca2+ in peat bog pore waters were found to yield significantly lower concentrations compared to inductively coupled plasma analyses of the same samples. Here, 20 mM methanesulfonic acid was used to acidify the pore waters to pH 2 prior to injection. Following this sample pretreatment, the measured concentrations of Na+, K+, Mg2+, and Ca2+ obtained by IC were significantly higher than in the unacidified samples and were in good agreement with the concentrations determined independently using inductively coupled plasma mass spectrometry.