Concentration Measurements of Natural Organics

Kainulainen et al. (1994) determined correlation coefficients for different analjtical methods (TOC, KMn04), colour, and fractions of humic matter were determined. Correlations were poor for smaller molecules, and NF and KMnCL produced the best results. Many oxidation processes transform larger humic molecules into smaller, more active fractions that are non-detectable. 

UV absorbance has been used for reasons of simplicity in many pilot plant studies. However, UV measures the aromatic compounds preferentially and does not give correct results if the aromaticity is altered, as is the case in most treatments. Values will be overestimated, as most treatment processes preferentially remove aromatic compounds. UV absorbance can therefore not be used to measure treatment efficiency. 

The UV/TOC ratio is often used to determine the humic fraction in the organic matter or to determine the aromaticit) of a sample. Different wavelengths of UV absorbance are used to measure colour (see Appendix 4). 

Fluorescence can also be measured for LMW compounds to determine concentrations, but discrepancies between UV and fluorescence were found for different MWs (fucker and Clark (1994)) and, again, results would var if samples are fractionated during treatment. Belin et al. (1993) found a higher fluorescence of smaller compounds such as FA and hydrophilic acids, compared to HA. A shift of intensity to shorter wavelengths with increasing salinity has been observed in fluorescence 

UV absorbance at particular wavelengths can be related to the presence of specific chromophores. Absorbance at 254 nm can be mainly correlated to the amount of double bonds in aromatic rings (Pettersson et al. (1994)) and, thus, to the aromaticity of a sample, whereas absorbance at 436 nm is more related to the concentration of unsaturated C=C, C=0, and N=0 units, chinones, keto-enol-tautomerie and complexed iron. Absorbance was observed to be highly pH dependent (Abbt-Braun et al. (1990)). Eaton (1995) subsequently developed a standard method to measure UV absorbance of natural waters. Korshin et al (1997b) correlated absorbance characteristics to the reactivit) of aromatic moieties with chlorine. Also, absorbance decreases after chlorination (Korshin et al (1996)). 

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