Liquid Chromatography — Organic Carbon Detection LC-OCD

This method was developed by Stefan Huber (Karlsruhe, Germany) and consists of three size exclusion chromatography columns which divide the organic carbon into several fractions as a function of size, but also hydrophobic and ionogenic characteristics. A sample of up to 3 mL is injected into the instrument and filtered in-line with a 0.45 )um filter. The deposit on the filter is backwashed after 5 minutes and directly analysed with the TOC analyser to determine the particulate organic carbon content (POC). 

SAC is the UV absorbance at 254 nm, CSAC is the UV absorbance of the chromatographable fraction, The faction UV/DOC, or SAC/OC, was calculated from the humic substance fraction and represents the aromaticity of the sample. 

The Gosford NOM contains hardly any polysaccharides and mostly pedogenic HS, which indicates a bog lake . Again, aromaticity and size are the most clear distinctions between the fractions, but the values are lower than those of the Suwannee River IHSS samples. 

Overall, the fractionation of the samples (using XAD methods) is not complete, neither in the case of the IHSS samples, nor in the case of the Gosford NOM. Therefore, there will always be an overlap of compounds, which is likely to make interpretation of results difficult. 

While the NOM and its fractions and the IHSS FA lie nicely in the region of FA isolates and pedogenic surface waters, Aldrich 100 kDa permeate and IHSS HA lie well outside this region. The NOM sample lies well above the samples from European rivers such as the Seine, Main, Rhine, and Karst. This can be explained with a relatively high input of small organics from wastewater treatment plants which are discharged into these rivers. Smaller and probably purer rivers such as the Steinbach or Kleine Kinzig are located close to the hydrophilic and FA fraction of NOM. 

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These effects were further investigated by size exclusion analysis (SEC) of the fractions (see section 6.4.8) and by liquid chromatography — organic carbon detection (LC-OCD) (see section 6.4.9). 

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