Figure 1
Supercritical carbon dioxide extract of unamended sandy soil (Idaho red sand) analyzed by ion pair HPLC For this separation we used a Supelco Discovery Amide C16 reverse phase column (15 cm × 4.6 mm, 5 μm). The elution method is described in the text; at the end of the run porphyrin was eluted with 100% acetonitrile. The filled chromatogram shows data from the optical detector (230 nm); the solid line chromatogram shows data from the electrochemical (amperometric) detector (ECD). For the ECD, the dual carbon electrode was set at two potentials: the first electrode was at -0.5 V and the second at +1.0 V. Signals from the second electrode were recorded. The ECD electrodes were polished at least once a day to keep the carbon electrode fresh for maximum sensitivity. The dashed line chromatogram shows optical data (230 nm) from extracted soil that had been heated at 600°C before extraction. Peaks for targeted redox signature compounds (nicotinamide, riboflavin, Q0, FMN, FAD, and porphyrin) were not observed in this control. Compounds identified in the chromatogram peaks of extracts of living soil (filled chromatogram and solid line chromatogram) are marked with flags and names. AU = Absorbance Units