1、 Definition of TOC

Total Organic Carbon， Total organic carbon, abbreviated as TOC, generally refers to the total amount of dissolved and suspended organic matter in water containing carbon. There are many types of organic compounds in water, which not only contain carbon, but also elements such as hydrogen, nitrogen, and sulfur, and cannot be completely separated and identified. Often referred to as' TOC '. TOC is a comprehensive indicator for rapid detection, which represents the total amount of organic matter in water in terms of carbon content. Due to the combustion method used for TOC determination, it can completely oxidize organic matter and more directly represent the total amount of organic matter. Usually used as an important basis for evaluating the degree of organic pollution in water bodies.

　　2、 TOC online analyzer

TOC analyzer refers to total organic carbon analyzer. A comprehensive indicator that represents the total amount of organic matter in water using carbon content. TOC can be directly used to represent the total amount of organic matter. Therefore, it is regarded as an important reference indicator for evaluating the degree of organic pollution in water bodies.

　　3、 Basic principles of TOC online analyzer

The basic principle is to first oxidize the carbon of organic matter in water into carbon dioxide, eliminate interference factors, and then measure it with a carbon dioxide detector. Then, data processing is used to convert the carbon dioxide gas content into the concentration of organic matter in water. After continuous research and experimentation, the TOC detection method has gradually evolved from traditional complex techniques to convenient and accurate.

　　4、 TOC detection method

There are various methods for detecting TOC, and the following are some common detection methods:

Combustion oxidation non dispersive infrared absorption method

　　Subtraction method:Introduce the sample and purified air into the high-temperature combustion tube and low-temperature reaction tube respectively. The water sample passing through the high-temperature combustion tube is subjected to high-temperature catalytic oxidation, which converts both organic compounds and inorganic carbonates into carbon dioxide; The water sample passing through the low-temperature reaction tube is acidified, causing inorganic carbonates to decompose into carbon dioxide. The generated carbon dioxide is sequentially introduced into a non dispersive infrared detector. Since a certain wavelength of infrared radiation can be selectively absorbed by carbon dioxide, and the intensity of carbon dioxide's infrared absorption is proportional to the concentration of carbon dioxide within a certain concentration range, the total carbon (TC) and inorganic carbon (IC) of the water sample can be quantitatively measured. The difference between total carbon and inorganic carbon is the total organic carbon (TOC) of 12

　　Direct method:After acidifying the water sample and aerating it, the inorganic carbonate is decomposed to generate carbon dioxide, which is then injected into a high-temperature combustion tube to directly measure the total organic carbon. However, due to the loss of volatile organic compounds in the water during the aeration process, measurement errors may occur. Therefore, the measurement result is only the organic carbon that cannot be blown out, not TOC12

Conductivity method

　　directconductivityLaw:The TOC content is determined by measuring the changes in conductivity caused by substances such as carbon dioxide produced by the oxidation of organic matter in water samples. But this method is relatively susceptible to interference from impurities such as acidity and halogenated organic compounds

　　Thin film conductivity detection method:Also known as selective conductivity method, the membrane used in the TOC analyzer can prevent the passage of impurities, ensuring that only the content of carbon dioxide is detected, thereby making the TOC reading more accurate. Its calibration results are stable and the detection accuracy is high

Gas Chromatography

Convert organic matter in water samples into gaseous form through specific methods, and then use gas chromatography to separate and detect these gaseous organic substances. Based on the retention time and peak area of each organic compound, combined with the chromatographic data of known standard substances, the type and content of organic compounds in the water sample are determined, and then the TOC value is calculated. This method can perform detailed analysis on complex organic mixtures, but the operation is relatively complex, requiring professional technicians and equipment, and the analysis time is relatively long.

Wet oxidation non dispersive infrared absorption method

Before oxidation, the test sample is treated with phosphoric acid to remove inorganic carbon. Then, organic carbon in the water sample is oxidized to carbon dioxide using oxidants such as persulfate. The concentration of the generated carbon dioxide is measured by a non dispersive infrared detector to obtain the TOC concentration. This method is commonly used for the determination of soluble organic carbon in water samples. For complex water samples, oxidation may not be sufficient and is not suitable for water samples with high TOC content. However, it is more suitable for conventional water samples such as surface water

UV oxidation non dispersive infrared detection method

Using ultraviolet light to irradiate the water sample, the organic matter in it is oxidized and decomposed into carbon dioxide, and then the TOC value is determined by measuring the content of carbon dioxide through a non dispersive infrared detector. This method is not suitable for water samples with high TOC content such as particulate organic matter and proteins, but it has the advantages of simple operation and speed

UV wet (persulfate) oxidation non dispersive infrared detection method

Combining the advantages of UV oxidation and wet oxidation, it is a synergistic method with better oxidation degradation effect than UV oxidation or wet oxidation alone. It can measure heavily polluted water samples, has wide applicability, wide measurement range, and mature technology

Resistance method

Under the premise of temperature compensation, the difference in resistivity of the sample before and after ultraviolet oxidation is measured to achieve TOC detection. This method has strict requirements for the source of water samples and can only be used for industrial water and pure water with relatively high cleanliness, with a relatively single application direction

UV absorption spectroscopy

Determine the TOC content by relying on the linear relationship between the UV absorbance value at 254nm and TOC in water. It has the advantages of fast, non-contact measurement, good repeatability, and low maintenance

Ozone oxidation method

By utilizing the strong oxidizing property of ozone, organic matter in water samples is oxidized into products such as carbon dioxide, and then the TOC content is determined by measuring the changes in related substances through appropriate detection methods. This method has a fast reaction speed, no secondary pollution, and promising application prospects

Ultrasonic cavitation sonoluminescence method

The use of high temperature, high pressure and other conditions generated by ultrasonic cavitation can decompose and transform organic matter in water samples. At the same time, the phenomenon of sonoluminescence can provide information about the reaction process and products, and then determine TOC through specific detection methods. This method has the advantages of no secondary pollution, no need to add reagents, and simple equipment