Figure 1: Types of Carbon

The total carbon mode can be used to detect all carbon forms of the sample, including both organic and inorganic forms. This mode does not involve sample acidification or blowing (see the "Inorganic Carbon" section below), which means that the original sample is tested in its original state.

The object of inorganic carbon mode is specific compounds, such asbicarbonateCarbonate, dissolved carbon dioxide, etc. Convert equilibrium to CO by blowing air or lowering pH₂State, inorganic carbon compounds are blown out. If the sample is not purged and acidified, inorganic compounds will remain in the solution and be counted as part of TC. This is a balanced relationship, and we will have a deeper understanding when we look at TOC.

In the total organic carbon mode, the total organic carbon (TC-IC=TOC) is obtained by subtracting inorganic carbon from the total carbon of the sample. Compared with other modes, TOC mode is more accurate and can reach ppb level or below.

The non blowable organic carbon mode is a commonly used mode for organic matter monitoring in process monitoring. In the NPOC mode, the sample is acidified to convert inorganic compounds into carbon dioxide. Then, use air free of carbon dioxide for blowing to remove inorganic compounds or washable compounds. Analyze the residual organic carbon (i.e. non blowable organic carbon) in the sample. If there is very little purgeable organic carbon (POC), then the total organic carbon is basically equal to the non purgeable organic carbon. The accuracy of non blowable organic carbon can reach the ppm level.

Can be blown or volatile organic compound mode for detecting volatility orSemi volatile organic compoundsThere are two ways to detect VOCs: using photoionization detection (PID) technology to directly detect VOCs; Calculate VOC using the formula VOC=TOC-NPOC. PID achieves the detection of volatile organic compounds by detecting positively charged carbon ions in the middle of sample blowing and separation. These ions are collected through electrodes and the generated current is detected. This mode can obtain the TOC value by summing the NPOC and POC results.

BOD and COD are two fundamental parameters that have been used for decades to determine organic matter content. BOD determines the amount of oxygen required for microbial degradation, while COD determineschemical oxidationThe amount of oxygen required for the presence of pollutants. These methods indirectly determine organic pollution by measuring the amount of oxygen consumed - BOD takes several days, COD takes several hours. Besides the long analysis time, both methods have compounds that may cause interference. Chlorine and salt can interfere with BOD, while sulfides, chlorides, nitrites, and divalent iron can interfere with COD. Some compounds can tolerate chemical oxidation of COD, such as benzene. Initially, BOD and COD values were obtained through laboratory testing, but due to the drawbacks mentioned earlier, there are now several analyzers that can provide these values through data correlation at specific locations. The TOC analyzer directly detects and quantifies the carbon present in the sample, and can provide real-time data converted into BOD and COD concentrations.