About the detection method of total organic carbon in water

Total organic carbon is a common water quality indicator of organic matter in water. It expresses the total amount of organic matter in water by the content of carbon. In fact, there are many types of organic matter in water, but these elements cannot be completely separated during detection. Since carbon is a common component of all organic matter, we can determine the pollution of organic matter by detecting the total organic carbon in water. And this is why total organic carbon is used to evaluate water pollution. Today we will learn about the method of determining the total organic carbon content in sewage by non-dispersive infrared method. The principle is to use combustion oxidation to inject the collected sewage samples into high-temperature combustion tubes and low-temperature combustion tubes, use catalysts to react organic matter, carbonate, bicarbonate and other carbon-containing substances in the water to generate carbon dioxide, and then pass through infrared gas detectors. Measure the total carbon content and inorganic carbon content, and finally calculate the total organic carbon content according to the formula. Reagents and equipment required for detection 1. Total carbon standard solution Weigh potassium hydrogen phthalate (2.215±0.002) g that has been dried at 110°C for 2 hours, dissolve it in laboratory pure water, transfer it into a 1000mL volumetric flask, and dilute with water To the mark, this solution contains 1 mg total carbon per 1 mL. 2. Inorganic carbon standard solution weighs anhydrous sodium carbonate (4.412±0.004) g and anhydrous sodium bicarbonate (3.497±0.003) g, these two reagents need to be dried in advance, dissolve these two reagents in water, Transfer to a 1000mL volumetric flask and dilute to the mark with laboratory pure water. 1 mL of this solution contains 1 mg of inorganic carbon. The prepared standard solution needs to be stored in the refrigerator. 3. Total organic carbon detector. 4. Micro injector 50ul, 100ul. 5. Compressed air cylinders. Water sample collection and pretreatment method The water sample should be analyzed immediately after collection, otherwise the organic compounds in the water will be oxidized or decomposed by microorganisms. If it cannot be detected in time, the water sample should be stored in a low temperature environment for preservation. If it is found that the total carbon concentration of the water sample is greater than the measurement range of the working curve, the water sample can be diluted with first-grade pure water that does not contain carbon dioxide. If the concentration of organic carbon in the water sample is very low and the concentration of inorganic carbon is high, then Or when the total carbon concentration is less than 10mg/L, you can take 20mL of the water sample and add a few drops of 50% hydrochloric acid to make the pH of the water sample 2. After passing through the purified air for 2-5 minutes to remove the inorganic carbon in the water, the detection is carried out. In the total organic carbon detection step, it is necessary to estimate the approximate content of total carbon in the water sample before detection, so that an appropriate sample volume can be selected. In the same water sample, use a micro-injector to take a sample and inject it into the total carbon sampling port, and then take a sample and inject it into the inorganic carbon sampling port, and then perform detection. When drawing the working curve of the total carbon working curve and diluting the standard series with the total carbon standard solution, you can choose multiple range concentrations such as 1mg/L-50mg/L, 20mg/L-100mg/L, 40mg/L-200mg/L, etc. At least 5 different concentrations of a set of standard solutions should be selected, and each concentration should be injected at least 3 times, and the average value should be taken. Then, the concentration is taken as the abscissa, and the measured voltage value is taken as the ordinate, and the values ​​of different concentration ranges are drawn. Total carbon working curve. Inorganic carbon working curve Turn the position of the switching valve on the instrument to inorganic carbon, dilute the standard series with inorganic carbon standard solution, and operate according to the drawing steps of the total carbon working curve to draw the working curve of inorganic carbon in different concentration ranges. Matters needing attention during detection 1. The inorganic carbon standard solution below 30mg/L in the detection should be prepared immediately after use to avoid oxidation due to long-term contact with air. 2. The water removal device of the instrument should be replaced regularly to prevent the water vapor generated after the water sample is burned from affecting the test results. 3. When the instrument is in normal use, when injecting water samples or standard solutions, if the parallel detection is not good, it is necessary to check whether the catalyst is invalid and replace it according to the instruction manual of the corresponding instrument.