The total organic carbon analyzer accurately distinguishes and measures different forms of organic carbon (such as dissolved organic carbon, particulate organic carbon, volatile organic carbon, etc.) in water samples through the synergistic effects of oxidation decomposition, detection technology, and sample pretreatment. Its core principles and implementation methods are as follows:
1、 Oxidative decomposition: unified conversion into detectable carbon dioxide
The core step of a total organic carbon analyzer is to oxidize different forms of organic carbon into carbon dioxide (CO ₂). Common methods include:
High temperature catalytic combustion method: At high temperatures of 680-950 ℃, platinum or cobalt trioxide is used as a catalyst to oxidize organic matter to CO ₂. This method is suitable for high concentration organic carbon samples (such as industrial wastewater) and can decompose recalcitrant organic compounds.
UV oxidation method: Using 185nm ultraviolet light to irradiate the sample, combined with persulfate catalyst, organic carbon is oxidized to CO ₂. This method is sensitive to low concentration samples, but difficult to handle high salinity or complex matrix samples.
Wet oxidation: Organic carbon is oxidized by a strong oxidizing agent (such as potassium persulfate) under heating conditions, which is easy to operate, but the oxidation efficiency is greatly affected by the composition of the sample.
2、 Detection technology: Quantify organic carbon through carbon dioxide concentration
The CO ₂ generated by oxidation is detected by the following techniques, combined with sample processing methods to distinguish different forms of organic carbon:
Non dispersive infrared detection (NDIR): CO ₂ selectively absorbs specific wavelengths of infrared light, and the absorption intensity is proportional to the concentration. By measuring the absorption value, the total organic carbon (TOC) content can be quantified.
Conductivity method: Using the change in conductivity of the sample before and after oxidation reaction, calculate the difference between total carbon and inorganic carbon, and indirectly obtain TOC. This method has strong anti-interference ability and is suitable for high salinity samples.
3、 Key method: Implement morphological differentiation and precise measurement
Subtraction method:
Principle: Inject the water sample into a high-temperature combustion tube (for measuring total carbon TC) and a low-temperature reaction tube (for measuring inorganic carbon IC). TOC=TC-IC， Can distinguish between dissolved organic carbon (DOC) and inorganic carbon.
Application: Suitable for conventional samples such as surface water and drinking water.
Direct method:
Principle: After acidification of the water sample, aerate to remove CO ₂ generated by IC, and then inject it into a high-temperature tube to measure the remaining organic carbon (NPOC, which cannot be blown out).
Limitations: May result in loss of volatile organic compounds, suitable for low volatility samples.
Filtering and acidification pretreatment:
Filtration: Use a 0.45 μ m filter membrane to separate DOC from particulate organic carbon (POC).
Acidification: Remove IC interference to ensure the accuracy of TOC measurement.
4、 Application scenarios and advantages
The total organic carbon analyzer can accurately distinguish different forms of organic carbon in water bodies through the above methods, providing key data for industries such as water quality monitoring, pharmaceuticals, and semiconductors. For example, in drinking water safety testing, the DOC content can be quantified to assess the risk of disinfection by-products; In industrial wastewater treatment, POC changes can be monitored to optimize the treatment process. Its high sensitivity (detection limit as low as 0.01mg/L) and anti-interference ability ensure the reliability of the results.