Total nitrogen reagent preparation
◆ Total nitrogen reagent (A) 100 samples: finished liquid reagent, no need to prepare, direct use;
◆ Total nitrogen reagent (B) 100 samples: finished liquid reagent, no need to prepare, direct use;
◆ Total nitrogen reagent (C) 100 samples: finished liquid reagent, no need to prepare, direct use;
Digestion device preheating:Turn on the power of the digester, select the total nitrogen digestion mode (125°C, 30min), press confirm (or start), and the digester will automatically heat up and preheat;
Concentration prediction:Before the test, the total nitrogen value of the water sample is first predicted, and the operation steps corresponding to the range are selected, for example, the total nitrogen concentration value is predicted to be 0-25mg/L, you need to select the 0-25mg/L range of the procedure; If the total nitrogen concentration is predicted to be 25-250mg/L, the procedure in the 0-250mg/L range is selected.
1. When the predicted value is in the range of 0 0- -2 25 L mg/L
If total nitrogen is present, the water sample will appear brownish-yellow, and the darker the color, the higher the concentration value of the water sample. Analytical procedure: total nitrogen L; Watch out for overrange tips!
2. When the predicted value is in the range of 2 25 5- - 25L 0mg/L
Dilute the water sample 10 times as the [sample to be tested] (e.g., take 1mL of water sample + 9mL of distilled water in an empty test tube, cover and shake well as the sample to be tested, and take 1mL at this time.)The sample to be tested is tested. Analytical procedure: total nitrogen H; Watch out for overrange tips!
3. When the predicted value exceeds 250 0 mgL /L
The water sample needs to be diluted to the corresponding concentration value in sections 1-2 above, and then operated according to the corresponding range, and the determination result is multiplied by the dilution factor.
4. Test steps on the computer
5. Precautions
◆ If there is total nitrogen, the water sample is brownish-yellow, and the darker the color, the higher the concentration value of the water sample.
◆ After adding the total nitrogen reagent, please cover, tighten and shake well in time, after the digestion is completed and cooled, before opening the cap, please shake the liquid fully again before opening.
Shake well:Please use the upside-down shaking method, that is, wait for the liquid to completely flow down and then turn the tube upside down again, do not shake and shake well.
◆ Pay attention to cross-contamination, use different measuring utensils for different liquids (pay attention to changing the tip when using a pipette).
◆ Use a suitable pipette to take the liquid, do not use a 5mL pipette to remove 2mL and less liquid, less than or equal to 2mL of liquid, it is recommendedPipette 2 times with a 1mL pipette.
◆ When using a pipette, it is necessary to calibrate the pipette frequently (it is recommended to do so once a week), and pay attention to replacing the tip during use.
◆ The protective cover must be covered during the heating and digestion process of the digester. During the digestion process, beware of scalding, pay attention to the high temperature area of the digester.
◆ After the digestion tube is taken out from the digester, take one piece at a time, it is forbidden to take out multiple tubes at the same time, pay attention to the high temperature, and prohibit shaking.
◆ The cooling process can be natural cooling or water cooling, but the temperature must be below 100°C to be water-cooled.
◆ The digested water sample must be completely cooled before proceeding to the next step.
◆ The digested sample tube must be clear and translucent (colored, but must not be turbid and free of suspended solids)
6. Collection and storage of total nitrogen samples
◼ Samples should be collected in a clean glass or plastic container with at least 100 mL of sample. The results are most reliable when analyzed immediately after sampling.
◼ The results are most reliable for analysis immediately after sampling. If this is not possible immediately, use sulfuric acid (2 mL of concentrated sulfuric acid/L water) to adjust the pH of the sample to 2 or 2under Save. Store samples at 4 °C. Samples can be stored for up to 28 days.
◼ Before sampling, the sample cell should be stirred evenly to collect a homogenized sample containing solid particulate matter to ensure that the sample is representative (total nitrogen is divided into total filterableNitrogen and total nitrogen. (1) Filterable total nitrogen: refers to the nitrogen content of soluble and filterable solids (less than 0.45μm particles) in water. (2) Total nitrogen: refers to solubleand nitrogen content in suspended particles. Therefore, the detection target should be clarified before sampling for testing. ）。
◼ Before testing and analyzing, heat the sample to room temperature, neutralize the sample acidity with a 5.0N sodium hydroxide solution, and adjust the pH of the sample to neutral. rootThe test results were corrected according to the increase in sample volume.
7. Methods review
The alkaline persulfate digestion process converts all forms of nitrogen into nitrate nitrogen. After digestion, sodium metabisulfite is added to remove halogensOxidizing substances. The nitrate reacts with the color-changing acid in a strongly acidic environment to form a yellow complex, which is positive in color with the total nitrogen concentrationThe total nitrogen value of the sample was calculated by spectrophotometry and microcomputer technology.
