In COD measurement, generally choose the Potassium Permanganate method and potassium dichromate method. These two methods are more troublesome. The new COD fast measuring instrument has the characteristics of fast and accurate, low energy consumption and easy operation. The 5B type intelligent COD fast measuring instrument is introduced as follows.
1. Measurement principle
The principle of COD rapid analyzer is to use a special reagent. It contains a kind of composite catalyst, that is, accelerating reaction, and also has anti-interference effect on chloride ion. Water samples and special reagents in the heating furnace undergo rapid redox reaction. The reaction turns the six valence chromium ions into trivalent chromium ions. The mass concentration is determined by spectrophotometry, and the corresponding COD value is obtained.
Two. The main technical performance
1) measurement range: 50-1000mg/l, if the COD value exceeds 1000mg/l, it can be diluted to the range of measurement and then measured again.
2) digestion time: 10min can be used to measure 20 water samples at the same time
3) temperature range: (165 + 15) C
4) accuracy: the surface water COD mass concentration is 20mg/l, the relative standard deviation is less than 10%, the sewage COD mass concentration is 300mg/l, the relative standard deviation is less than 4.3%
5) power consumption: about 150W
6) anti chlorine interference: chloride ion concentration less than 900mg/l has no effect on the determination results, the specific chloride ion mass concentration is less than 10000mg/l, when the chloride ion mass concentration is greater than 900mg/l, it can be diluted.
7) power supply: (220 + 20) V, 50Hz
8) adaptation environment: the relative temperature of the environment is greater than 80%, and the ambient temperature range is between 5-40 degrees C
Three. Preparation for work
1. Instrument preparation
The timing dial at infinity, the COD tester instructions preheat 30min, to be heated by the bright lights dimmed, the temperature reaches stable, the actual temperature on the thermometer indicator, with keys to mediation, so that the actual temperature stability in (150 + 2) C
Press the 2min key to check whether the timing is 2min + 20s
Press the 10min key to check whether the timing is 10min + 20s
2. Cleaning and drying of the reaction tube
When the reaction tube is used for the first time, the special reagent has been loaded into the reaction tube. At this time, it can be used directly. The second time use must be washed with tap water, then washed with distilled water, and then the special reagent can be added into the tube after drying.
3. Determination of preparation
Four. Experimental operation
1) the reaction tube with special reagents is inclined to 45 degrees, and the 2ml water sample is injected once with the 2ml pipette
2) clean the outer wall of the reaction tube with deionized water and dry it with filter paper
3) the upside down reaction tube is several times, and the internal reactants are mixed evenly.
4) put the reaction tube into the reactor in turn and heat the 2H
5) use deionized water instead of water sample, repeat operation step 1-4
6) when the COD detector alarm, turn off the reactor and wait for 20min to make the reaction tube temperature lower than 120.
7) take out the reactor and turn it upside down and then cool it to room temperature.
8) the blank solution is placed in No. 0 colorimetric dish, and the water sample is placed in 1,2,3 as the blank reference solution. In a Petri dish, the spectrophotometer wavelength is tuned at 620nm, and the absorbance value of the blank reference liquid is adjusted to 0 with the 100% knob.
9) the water sample is pushed into the water sample and its absorbance A value is measured. Then the mass concentration of the sample COD is (mg/l) 1505 x A
1) the reaction tube used in the experiment is usually washed with tap water and then washed and dried with distilled water.
2) when a number of samples are continuously measured, the measured solution of the colorimeter can be poured out of one corner and then poured into the new solution to be measured. The resulting error is within the allowable range.
3) when the solution is poured from a Petri dish, do not splash the solution on the window surface that is transparent to a Petri dish. Before colorimetric determination, we should check whether the window is clean. In addition to the visual inspection, we can detect the A value of each colorimeter and see whether the relative value is consistent. After reading the number stable, we will read again.
4) in order to make the solution evenly, pour the solution into the cuvette, and then back into the reaction tube, then pour into the cuvette