The organic carbon in water and wastewater is composed of a variety of organic compounds in various oxidation states. Total organic carbon (TOC) is a convenient and direct expression of total organic content. TOC is independent of the oxidation state of the organic matter and does not measure other organically bound elements, such as nitrogen and hydrogen, and inorganics that can contribute to the oxygen demand. Measurement of TOC is of vital importance to the operation of water treatment and waste treatment plants. In many applications, the presence of organic contaminants may degrade ion-exchange capacity, serve as a nutrient source for undesired biological growth, or be otherwise detrimental to the process for which the water is to be utilized. For drinking waters in particular, organic compounds may react with disinfectants to produce potentially toxic and carcinogenic compounds. To determine the quantity of organically bound carbon, the organic molecules must be broken down and converted to a single molecular form that can be measured quantitatively. TOC methods utilize high temperature, catalysts, and oxygen, or lower temperatures (<100°C) with ultraviolet irradiation, chemical oxidants, or combinations of these oxidants to convert organic carbon to carbon dioxide. The carbon dioxide may be purged from the sample, dried, and transferred with a carrier gas to a nondispersive infrared analyzer or coulometric titrator. Alternatively, it may be separated from the sample liquid phase by a membrane selective to carbon dioxide into a high-purity water in which corresponding increase in conductivity is related to the carbon dioxide passing the membrane. Many instruments utilizing persulfate oxidation of organic carbon are available. They depend either on heat or ultraviolet irradiation activation of the reagents. These oxidation methods provide rapid and precise measurement of trace levels of organic carbon in water. Organic carbon is oxidized to carbon dioxide, by persulfate in the presence of heat or ultraviolet light. The carbon dioxide produced may be purged from the sample, dried, and transferred with a carrier gas to a non-dispersive infrared (NDIR) analyzer, or be coulometrically titrated, or be separated from the liquid stream by a membrane that allows the specific passage of carbon dioxide to high-purity water where change in conductivity is measured and related to the carbon dioxide passing the membrane.
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|Hold Times, Preservatives, Preps, Collection, Analytical & Documentation|
|Holding Time:||None noted in method.|
|Preservatives:||None noted in method.|
|Required Preps:||Glass bottle.|
|Collection Method:||Grab sampling.|
|Analytical Methodology:||Ultraviolet or heat irradiation, followed by non-dispersive infrared (NDIR) analysis or coulometric titration.|
|Analyte||Formula||CAS Number||Detection Limit|
|Total Organic Carbon|
* The analytes and detection limits listed for each method represent the typical detection limits and analytes reported for that particular method. Keep in mind that analyte lists may vary from laboratory to laboratory. Detection limits may also vary from lab to lab and are dependent upon the sample size, matrix, and any interferences that may be present in the sample.
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