E-mail: michael@shboqu.com   |   Expert in Water Quality Measurement and Water Treatment Project

About the Determination Principle of Total Organic Carbon

by:BOQU     2023-03-16
Our life is inseparable from water. There are quite a lot of organic pollutants in water, which will directly affect the quality of water bodies and cause harm to our life and production. Therefore, the monitoring of water and wastewater has attracted more and more attention. Among them, the detection of total organic carbon (TOC) content in water has attracted increasing attention. It is a comprehensive index that expresses the total amount of organic matter in water with carbon content, and directly reflects the degree of water body pollution by organic matter. At present, health and epidemic prevention and water quality monitoring departments are paying more and more attention to the pollution of organic matter in water. Determination principle of total organic carbon Total organic carbon (TOC) is determined by a special instrument - total organic carbon analyzer. The TOC analyzer is to oxidize the total organic carbon in the aqueous solution to carbon dioxide, and measure its content, and use the corresponding relationship between carbon dioxide and total organic carbon to quantitatively measure the total organic carbon in the aqueous solution. The TOC analyzer is mainly composed of the following parts: sample inlet, inorganic carbon reactor, organic carbon oxidation reaction (or total carbon oxidation reactor), gas-liquid separator, non-spectral infrared CO2 analyzer, and data processing part. According to different working principles, the instrument can be divided into combustion oxidation-non-dispersive infrared absorption method, conductivity method, gas chromatography and so on. Among them, the combustion oxidation-non-dispersive infrared absorption method only needs one-time transformation, the process is simple, the reproducibility is good, and the sensitivity is high. Therefore, this TOC analyzer is widely used at home and abroad. According to the different principles of measuring TOC value, the combustion oxidation-non-dispersive infrared absorption method can be divided into subtraction method and direct method. 1. The principle of the subtraction method to determine the TOC value The water samples are respectively injected into the high-temperature combustion tube (900°C) and the low-temperature reaction tube (150°C). The water sample passed through the high-temperature combustion tube is subjected to high-temperature catalytic oxidation, so that both organic compounds and inorganic carbonates are converted into carbon dioxide. The water sample passing through the reaction tube is acidified to decompose the inorganic carbonate into carbon dioxide, and the generated carbon dioxide is sequentially introduced into the non-dispersive infrared detector, so as to measure the total carbon (TC) and inorganic carbon (IC) in the water respectively. The difference between total carbon and inorganic carbon is the total organic carbon (TOC). 2. The method principle of direct method to measure TOC value. After the water sample is acidified and aerated, various carbonates are decomposed to generate carbon dioxide and removed, and then injected into the high-temperature combustion tube, the total organic carbon can be directly measured. However, due to the loss of volatile organic compounds in the water sample during the aeration process, measurement errors occur, so the measurement result is only the organic carbon value that cannot be blown out. 3. The conductivity method uses a UV lamp to convert organic matter in water into carbon dioxide, which dissolves in water to form carbonate ions. The conductivity is measured before and after the conversion of organic matter, and the increased carbonate content can be calculated through the difference in conductivity, and the TOC in the water can be calculated.
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