In recent years, as the country attaches great importance to the field of environmental protection, the "permanganate index CODmn (oxygen consumption)" in water has increasingly become one of the daily inspection indicators for water quality monitoring laboratories at all levels.

Permanganate index (oxygen consumption) is a conditional index experiment. Manual methods have many shortcomings: for example, the digestion process requires manual timing; water replenishment is time-consuming and unstable; the titration endpoint is difficult to identify, which affects the accuracy; batch analysis requires high quality and ability of operators.

The fully automated instrument detects the permanganate index (oxygen consumption), which is a new product developed by domestic enterprises in recent years. At present, there is a certain market in all parts of the country but it has not yet been widely used. From the usage point of view, the feedback from most users is good, which can replace manual experiment and greatly improve work efficiency. For example, this is a set of data comparison between our company's ST108M automatic permanganate index analyzer and a manual method adopted by an environmental monitoring station in a certain city in Jiangsu.

Conclusion: Whether it is a standard sample or an actual sample, the relative standard deviation ( RSD) of the fully automated instrument is better than the manual method, and the data is more precise and accurate.

With the advancement of science and technology, it has become an unstoppable trend to replace manual operations with automated instruments. But how to choose a fully automatic permanganate index (oxygen consumption) analyzer?

The author suggests that you can consider from the following aspects:

First: The number of sample trays and digestion positions of the instrument.

Many new users often feel that the more sample trays and digestion bits, the better; in fact, this is not the case. The number of sample trays is not proportional to the position of the digestion holes. It is not that the more digestion holes, the faster the detection speed; in fact, the number of samples tested by each unit is different, and some have thousands of samples per month; some dozens per month A. Too much idleness is less insufficient, so the choice of sample tray depends on the unit's inspection task; and the number of digestion bits has nothing to do with the number of sample trays, but is related to the titration and endpoint identification unit. For example, if vehicles pass through a high-speed toll gate, no matter how many lines they are in, if there is only one passway, traffic jams will become more and more serious; if you want to improve the efficiency of passage, only opening a few more passways is the correct solution. In the same way, if you want to increase the detection speed, it depends on the titration and endpoint recognition system after the digestion procedure. At present, the detection speed of single drop positioning and single end point identification position of mainstream products on the market is generally about 7.5-8 minutes for each sample; double drop positioning and double end point determination position are about 5-6 minutes;

Second: automatic sample quantitative function. At present, this function is a shortcoming of domestic enterprises, and many enterprises do not have the function of automatic sample quantification. The water samples need to be measured one by one with a graduated cylinder and then poured into the sample cup, which requires repeated cleaning and the process is cumbersome;

Our company pioneered the automatic sample quantitative function of the automatic permanganate index tester. The operator only needs to pour the collected water sample into the sample cup, and the remaining work is automatically completed by the instrument, which greatly improves the work efficiency of the project and reduces the work intensity of the operator;

Third: heating tools or methods. GB5750 and GB11829 both stipulate the use of water bath heating method, so mainstream manufacturers have adopted this design, but the water consumption in the sample digestion process is relatively large, so the water tank should be designed with automatic water replenishment function. However, it is recommended not to use the electrode method used by individual manufacturers to measure the upper and lower limits of the water level. Otherwise, only tap water can be added. Long-term use may easily cause scale and corrosion of the water tank.

Fourth: the choice of reagent pump.

In the process of reagent addition and titration using the automatic permanganate index tester, the industry usually uses a syringe pump as a tool for high-precision addition of reagents, but the disadvantage is that the cost is relatively high. A few manufacturers initially used peristaltic pumps, but quickly gave up, unable to meet the experimental requirements, so they had to use the same type of rotary pumps, but the accuracy was still worse than that of syringe pumps;

Our company uses an imported high-precision syringe pump, the titration accuracy error is less than three thousandths, the uniquely designed titration head structure, each drop can be accurate to 0.01ml.

Fifth: The choice of end point recognition sensor.

At present, mainstream manufacturers have adopted color sensors that replace the human eye to identify the end point of titration. The advantage is that it is consistent with the national standard, and the titration end point is determined by identifying the color of the water sample; but the cost of the color sensor almost determines the manufacturer's product positioning and reliability. Costs vary greatly, ranging from several thousand yuan to tens of thousands of yuan. Ordinary color sensors can only judge the end point by color mutations in the three colors of RGB. The color changes of water samples are detected by far-infrared rays. This type of rays is easily affected by external factors, such as the brightness of the titration work environment, cups The external wall-mounted water needs to be heated to eliminate; and this ordinary RGB three-color sensor is suitable for water samples with complex components, such as turbid water samples, water samples with suspended solids, and high-chlorine water samples (after the digestion is completed, the sodium oxalate is added and the reaction is completed. For brown precipitates, the color of the end point will be unstable due to the consumption of potassium permanganate by chloride ions during titration, and the instrument needs to repeat the titration.) The titration process cannot be accurately identified and cannot be completed.

Our company adopts imported high-precision full-color gamut vision sensor, which can not be affected by turbidity, sample cup, background, light and other factors. Using powerful image analysis and processing functions, the response speed is fast, and the end color of complex water samples can be adjusted. Perform separate processing (see the figure below, to meet the color judgment of different water samples by switching the program.)

Sixth: the choice of price.

At present, the positioning of mainstream manufacturers generally ranges from 200,000 to 400,000 yuan. It is related to the number and configuration of samples that can be tested.

Finally, thank you all for your patience and reading this article. The appearance of the fully automatic permanganate index (oxygen consumption) tester is a technological innovation in the field of instrument testing by domestic enterprises, which is better than Similar imported products. The state actively encourages this kind of technological innovation that guides the progress of the industry, and is also improving the revision of relevant standards. I hope everyone can support domestic enterprises in an attitude of tolerance, generosity and encouragement, so that these enterprises can do better and go further!