Abstract
This project arose out the need for a simple method to analyse natural organic matter (NOM) on a routine basis. Water samples were obtained from the Vaal Dam. Analysis was preceded by separating the NOM into the humic and non-humic fractions. The humic portion was separated further into two fractions by employing a non-ionic DAX-8 resin to separate humic acid from fulvic acid. High-performance size-exclusion chromatography (HPSEC), equipped with a UV detector and an evaporative light scattering detector (ELSD) was used to obtain information on the molecular weight distribution and concentration levels of the two acids. Mixed standards of polyethylene oxide/glycol were employed for calibration. The molecular weight distributions (MWDs) of the isolated fractions of humic and fulvic acids were determined with ELSD detection as weight-average (Mw), number-average (Mn) and polydispersity (ρ) of individual NOM fractions. The Mw/Mn ratio was found to be less than 1.5 in all fractions, indicating that they have a low and narrow size fraction. It is noted that the ELSD detector proved to be far more capable than the UV detector. A finding of interest is that 40% of the total organic carbon in the dam water samples could be attributed to humic substances. The developed method successfully separated the humic substances from water and further separated the humic substances into the component acids, namely, humic and fulvic acids. Molecular weight distribution of these compounds is a powerful indication of how much DOM was present in the dam water. Even though the UV method was useful in characterizing these substances, the ELS detector is recommended because it detects all the organic species present. Keywords: Natural organic matter, dam water, determination, ELSD
Highlights
The South African national power utility, Eskom, has the onerous task of generating and supplying electrical power to 9 provinces in South Africa and some neighbouring states
High SUVA values indicate the presence of humic substances, while low SUVA values indicate the presence of organic matter which is measurable by dissolved organic carbon (DOC) and total organic carbon (TOC) but does not impact colour or absorb UV light
There is a limited range of molecular weights that can be separated by each column and the size of the pores for the packing should be chosen according to the range of molecular weights of the analytes to be separated
Summary
The South African national power utility, Eskom, has the onerous task of generating and supplying electrical power to 9 provinces in South Africa and some neighbouring states. To this end, it has built a number of power stations, of which the majority are coal fired. One source of acidic impurities is natural organic matter; the humic and fulvic acid portions. This project focused on developing a relatively simple method for the routine identification of pre-selected organic species present in the raw water.
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