Explanation of common problems in the detection process of water quality COD detector
Water sample collection
1. Prepare the sampling device and container before sampling. The sampling devices currently in use are mainly water buckets and various water collectors. If the sampling device is plastic or glass, it can be cleaned and used according to the general cleaning method of the container; if it is iron, it is necessary to completely remove the oil stain with detergent, then rinse with tap water, and dry it for use. However, the water samples taken cannot be used for the analysis of metals such as iron and nickel.
2. The number of samples depends on the measurement items. Different cod detectors have different requirements on the consumption and storage conditions of water samples. Therefore, the required amount should be calculated according to the actual situation of the measurement item, and increased by 20~30% on the basis of the actual sampling amount. If the volume of the sampling container is limited, one sampling can not meet the required sampling volume, you can sample multiple times, mix in a larger container, and then load the sample container.
3. Sampling method The collection method of the water sample is closely related to the analysis result. Water samples must be representative in order to truly reflect the water quality of the entire body of water.
4. Before testing, the collected water samples should be shaken or mixed with other methods to avoid problems such as precipitation caused by long-term storage.
5. In the investigation of water pollution, the collection of COD detectors in water samples should consider the entire water area, set up sampling points reasonably, establish a water pollution monitoring network, and report the pollution of water areas and the dynamic changes of various harmful substances in a timely and accurate manner.
Water samples of different water quality need a certain time from collection to analysis and determination. The time difference may range from a few minutes to several hours, and sometimes it will be shelved for a few days. Due to changes in environmental conditions, microbial metabolism and chemical effects, certain physical parameters and chemical components of the water sample will change, resulting in inaccurate cod detection results. In order to minimize these changes, the transportation time must be shortened, analyzed and measured as soon as possible, and necessary protective measures must be taken; some items must be measured at the sampling site.
(1) Transportation of water samples Each water sample collected should be recorded and labeled on the sampling bottle and transported to the laboratory. During transportation, the following points should be noted:
1. Tighten the plug of the sampling container, if necessary, seal it with sealing glue and paraffin (water samples for oil testing cannot be sealed with paraffin).
2. In order to avoid the loss or contamination of the water sample due to vibration and collision during transportation, it is best to pack the sample bottle and squeeze it with foam or paper strips.
3. For samples that need to be refrigerated, a special insulated container should be equipped, put a refrigerant, and place the sample bottle in it.
4. Insulation measures should be taken in winter to avoid freezing and cracking of sample bottles.
(2) Preservation of water samples The container for storing water samples may adsorb the components to be measured, or the COD detector of the contaminated water samples, so choose containers made of materials with stable performance and low impurity content. Commonly used container materials are borosilicate glass, quartz, polyethylene and polytetrafluoroethylene. Among them, quartz and polytetrafluoroethylene have low impurity content, but are expensive. Generally, containers made of polyethylene and borosilicate glass are widely used in routine monitoring. For water samples that cannot be transported in time or analyzed as soon as possible, appropriate storage methods should be adopted according to the requirements of different monitoring projects. The transportation time of water samples is usually 24 hours as the maximum allowable time.
(3) Laboratory analysis stage Different types of water quality and different monitoring items have different sample pretreatment processes. Many monitoring projects for groundwater and surface water can be directly measured without pretreatment. The more polluted industrial wastewater and domestic sewage, different monitoring projects of COD detectors may require pretreatment operations such as filtration, precipitation, digestion, distillation, extraction, etc., which must not be omitted. Otherwise, large errors will occur in the analysis process and analysis results. Each batch of samples is analyzed with the standard samples of the National Environmental Monitoring Station or the Provincial Environmental Monitoring Center Station. Generally, as long as the analysis results of the standard samples are within the allowable error range, the sample analysis is qualified, and the calibration of the measuring instrument is generally ignored. The larger the capacity of the gauge, the smaller the relative error of its capacity. Therefore, large-capacity containers should be used as much as possible. In addition, when choosing glassware, you should try to use class A glass measuring device to avoid the use of measuring devices of different levels.
(4) Concluding remarks Water quality testing, as one of the important links of environmental protection, should attract attention, not just to meet environmental protection requirements, we need to care for this cause from the bottom of our hearts, strengthen our operational capabilities and theoretical knowledge, and allow water quality testing The COD detector is more accurate. Beijing Shuanghui Jingcheng Electronic Products Co., Ltd. specializes in the development and production of water quality environmental monitoring instruments. At present, it is one of the domestic product manufacturers with technical level and scale strength. In 2001, the self-developed water quality measuring instrument integrating measurement, calculation and colorimetry was put on the market. Soon it was recognized by the market. It changes the situation that only the digestion device in the market is more convenient, and a large number of measurement results still need to use a photometer and manual calculation. In 2002, the 12V power supply method was applied to water quality measuring instruments in the industry. COD (Chemical Oxygen Demand) Tester, COD Tester, NH3 Tester, Multi-parameter Water Quality Tester, Turbidity Colorimeter and Aquaculture Tester, etc., are independently developed and manufactured by our company. And in line with the People's Republic of China Environmental Protection Industry Standard HJ/T 399-2007 and "Water and Wastewater Monitoring and Analysis Method" (Fourth Edition) published in 2002, the fast closed catalytic digestion method (including photometric method), this method is designated as B Class method. After in-depth domestic research and verification by multiple laboratories, it is proved to be a more mature and unified method. Both A and A methods can be used in environmental monitoring and law enforcement.