Appendix I – Use of refraction index and UC detectors in the HPLC analysis
In the HPLC analysis, the refraction index (RI) spectrum was always used to check for the presence of peaks in the UV spectrum, as all compounds cause a change in refractive index, while only carboxylic acids absorb in the UV spectrum. In the mineral medium, glucose was quantified from the RI spectrum, and organic acids from the UV spectrum. A significant peak of succinate in the UV was not present in the RI spectrum, thus is not quantified from UV.
In the complex medium, acetate and succinate were quantified from the RI spectrum. At the retention time of these two compounds, a peak was present in the UV spectrum when running a sample of the combined medium A and B, indicating the presence of UV absorbing compounds in the influent.
For the cycle analysis, samples of the complex medium, propionate and butyrate were quantified using RI detection, since absorbance on the UV channel was poor for these peaks. For the cycle analysis, measurements of samples of mineral medium, acetate and butyrate concentrations were obtained from the RI channel.
For the lactate pulse experiment in the complex medium enrichment, acetate and lactate were quantified from the RI spectrum.