TOC analyzer
Total Organic Carbon (TOC) is measured by a specialized instrument called Total Organic Carbon Analyzer (TOC analyzer). TOC analyzer has the advantages of simple process, good reproducibility, high sensitivity, stable and reliable, generally does not consume chemicals in the measurement process, and does not produce secondary pollution or oxidation.
The measurement principle is based on converting different forms of organic carbon into easily quantifiable carbon dioxide through oxidation, and using the corresponding relationship between carbon content and total organic carbon to quantitatively determine TOC in aqueous solutions. According to different working principles, it can be divided into combustion oxidation non dispersive infrared absorption method, conductivity method, gas chromatography method, wet oxidation non dispersive infrared absorption method, etc. Among them, combustion oxidation non dispersive infrared absorption method only requires one-time conversion, has a simple process, good reproducibility, high sensitivity, and is widely used. The national standard GB13193-91 in our country adopts the combustion oxidation non dispersive infrared absorption method.
TOC determination is usually divided into direct determination method and indirect determination method. The direct determination method is generally a method of measuring total carbon (TC) by removing inorganic carbon (IC), which is suitable for measuring water samples with high IC content, but it is prone to losing volatile organic carbon (POC) in the water sample.
TOC analyzer
Detection method:
1、 Wet oxidation (persulfate) - Non dispersive infrared detection (NDIR)
This method involves treating the sample with phosphoric acid before oxidation to remove inorganic carbon, and then measuring the concentration of TOC. In modern TOC continuous analyzers, the vast majority are wet oxidation methods. Wet oxidation is not sufficient for complex water bodies (such as humic acid, high molecular weight compounds, etc.), so it is not suitable for water bodies with high TOC content. However, it is possible for conventional water bodies such as surface water.
2、 High temperature catalytic combustion oxidation non dispersive infrared detection (NDIR)
The application time of high-temperature catalytic combustion oxidation is much later than that of wet oxidation, but because high-temperature combustion is relatively efficient, it can be applied to heavily polluted water bodies such as rivers, seawater, and industrial wastewater.
3、 UV Oxidation Non Dispersive Infrared Detection (NDIR)
The method is the same as wet oxidation, but it uses the principle of ultraviolet light (185nm) irradiation to remove inorganic carbon before the sample enters the ultraviolet reactor, obtaining more accurate results. UV oxidation method is not suitable for high TOC content such as particulate organic matter, drugs, proteins, etc., but it can be used for water bodies such as raw water and industrial water.
4、 UV Wet Oxidation Non Dispersive Infrared Detection (NDIR)
This method involves the synergistic effect of UV oxidation and wet oxidation, complementing and promoting each other. The oxidation degradation effect is superior to either method. UV oxidation cannot be used for high TOC water bodies, and the synergy of the two can measure heavily polluted water bodies. Due to its strong applicability and wide measurable range, it has high popularity and mature technology.
5、 Resistance method
This method is a technology that has been applied in recent years. Its principle is to measure the difference in resistivity of the sample before and after ultraviolet oxidation under the premise of temperature compensation. However, this method has strict requirements for the source of the measured water, and can only use relatively clean industrial water and pure water, with a single application direction.
6、 UV method
The use of UV absorption spectroscopy for TOC detection and analysis can be traced back to 1972. Dobbs et al. studied the linear relationship between the UV absorbance value (A) at 254nm and the TOC of secondary effluent and river water from urban sewage treatment. After decades of development, the application of this method has developed rapidly due to its advantages such as fast, non-contact measurement, good repeatability, and low maintenance.
7、 Conductivity method
The main component involved in this method is the conductivity cell, which consists of a reference electrode, a measuring electrode, a gas-liquid separator, an ion exchange resin, a reaction coil, NaOH conductivity solution, etc. The advantages of conductivity cell are low price and easy accessibility, but poor stability.
8、 Ozone oxidation method
By utilizing the strong oxidizing property of ozone and using ozone oxidation as the detection technology for TOC, it has fast reaction speed, no secondary pollution, and high application value. Therefore, the application prospects of this method are very promising.