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TOC Analysis of Humic Acid: Sample Preparation is the Key
Industry: Environmental
Instrument: Apollo 9000 Total Organic Carbon (TOC) Analyzer, Phoenix 8000 Total Organic Carbon (TOC) Analyzer
Measuring the amount of natural organic matter (NOM) in sources of surface waters has been of particular interest for municipal drinking water purification and wastewater facilities. When raw water containing NOM is chlorinated in the disinfection process, potential carcinogens known as disinfection by-products (DBPs), such as trihalomethanes and haloacetic acids, are formed. In an effort to reduce NOM before disinfection, a direct correlation between Total Organic Carbon (TOC) and NOM has been established per Standard Methods 5310 and the USEPA’s disinfectants/disinfection by-products rule. With the increased importance placed on Total Organic Carbon (TOC) analysis of source water, a historical question of how much NOM can be recovered using Total Organic Carbon (TOC) has resurfaced. Humic acid, a component of NOM, has been suggested as a standard for mimicking NOM in the laboratory. However historically, persulfate oxidation Total Organic Carbon (TOC) analyzers have shown an acceptable recovery rate, 80–85%, for this difficult compound. Modern persulfate Total Organic Carbon (TOC) analyzers have shown even better recovery, 90–95%, with the use of optimized UV lamps and stronger concentrations of the persulfate reagent. However, no paper to date has fully explored and documented the root causes for variations in recovery in these analyzers.
In this paper, the optimization of a modern UV persulfate Total Organic Carbon (TOC) analyzer for humic acid recovery was evaluated with a comparison to a modern, high temperature combustion (HTC) Total Organic Carbon (TOC) analyzer. In the performance of Total Organic Carbon (TOC) analysis, UV persulfate instrumentation demonstrated 95% recovery of humic acid consistently across a linear range of 1 to 100 ppmC, the range typically found in the NOM of source water. Experimental data showed the key challenge for increasing humic acid recovery was representative sample transfer of this particulated matrix, after the acidification employed in the inorganic carbon (IC) removal step, rather than oxidation of the humic acid.
Applications
