Size, Molecular Weight, Radii of Gyration, Polydispersity

4 Size, Molecular Weight, Radii of Gyration, Polydispersity 

molecular weight, radii of gyration and polydispersity are all interrelated. Size is an important characteristic in water treatment, as diffusion coefficients and removal efficiencies are direedy dependent on the size of a solute. A large number of methods exist to measure these important parameters though results vary gready. Each method has its own limitations. 

Chromatographic techniques are very commonly used in the characterisation of natural waters (Aoyama (1996a, 1996b), Huber (unpublished), Shaw et al. (1994), Mori (1988), Becher et al. (1985), Amy et al. (1987)). However, most authors use different techniques, detectors, standards and eluents, making the comparison of results difficult. 

Humic material from bank filtered lake water has been divided into six fractions using size exclusion chromatography (SEC) coupled with HPLC and UV absorbance (254 nm), and a MW of around 10 kDa was determined (Kainulainen et al. (1994)). Shaw et al (1994) used gel filtration chromatography (GFC) to study apparent molecular size and found a decrease in size with decreasing pH. 

Frimmel and Hesse (1996) combined gel permeation liquid chromatography (GPLC) with UV and DOC detectors to separate natural organics into different groups. This was possible due to the relatively high sensitivity of the detectors used. 

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