In water quality determination, we found that the existence of Cl- seems causing a increase in the TOC determination data. Is anybody know the reason?
Total Organic Carbon (TOC) – material derived from decaying vegetation, bacterial growth, and metabolic activities of living organisms or chemicals and TOC in source waters comes from decaying natural organic matter (NOM) as well as synthetic sources. Humic acid, fulvic acid, amines, and urea are examples of NOM. Some detergents, pesticides, fertilizers, herbicides, industrial chemicals, and chlorinated organics are examples of synthetic sources.
Before source water is treated for disinfection, TOC provides an estimate of the amount of NOM in the water source. In water treatment facilities, source water is subject to reaction with chloride containing disinfectants. When the raw water is chlorinated, active chlorine compounds (Cl2, HOCl, ClO−) react with NOM to produce chlorinated disinfection byproducts (DBPs) that cause increse of TOC.
Dear Wendong Wang, what kind of TOC analyzer are you using? In most devices, the carbon dioxide generated by the total combustion of the sample is detected using an infrared gas analyzer. However, other TOC Analyzers remove the CO2 by diffusion through a selective membrane into deionized water and then measure the ionized CO2 by a conductivity cell using the Membrane-Conductometric method. If this is your case, maybe some trace of chlorides could interfere/enhance the signal.
I agree with the comment by Dr. Contreras. Additionally it can be interesting to know if the TOC analyser is using heat+oxygen or UV+persulphate to convert the organic matter to CO2.
I have experienced some problems with chloride in samples with the UV+persulphate method, but it wasn't increased values.
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