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The easiest way to measure ammonia nitrogen in the laboratory

by:BOQU     2023-03-19
①Water sample pretreatment: Take 250mL water sample (if the ammonia nitrogen content is high, you can take an appropriate amount and add water to 250mL, so that the ammonia nitrogen content does not exceed 2.5mg), transfer it into a Kjeldahl flask, add a few drops of bromothymol blue indicator solution, Adjust the pH to about 7 with sodium hydroxide solution or hydrochloric acid solution. Add 0.25g of light magnesia and several glass beads, connect the nitrogen ball and the condenser immediately, and insert the lower end of the catheter under the liquid surface of the absorption liquid. Heat and distill until the distillate reaches 200mL, stop the distillation and set the volume to 250mL. When using acid titration or Nessler colorimetry, use 50mL boric acid solution as the absorbing liquid; when using salicylic acid-hypochlorite colorimetric method, use 50mL 0.01mol·L-1 sulfuric acid solution as the absorbing liquid. ② Drawing of standard curve: Pipette 0, 0.50, 1.00, 3.00, 5.00, 7.00 and 10.0mL ammonium standard solution into 50mL colorimetric tubes respectively, add water to the marked line, add 1.0mL potassium sodium tartrate solution, and mix well. Add 1.5mL of Nessler's reagent and mix well. After standing for 10 minutes, measure the absorbance at a wavelength of 420nm with a cuvette with an optical path of 20mm and water as a reference. After subtracting the absorbance of the zero-concentration blank tube from the measured absorbance, the corrected absorbance is obtained, and a standard curve of ammonia nitrogen content (mg) versus the corrected absorbance is drawn. ③ Determination of water samples: a. Take an appropriate amount of water samples pretreated by flocculation and sedimentation (so that the ammonia nitrogen does not exceed 0.1mg), add it to a 50mL colorimetric tube, dilute to the marked line, and add 0.1mL potassium sodium tartrate solution. The following is the same as the drawing of the standard curve. b. Take an appropriate amount of the distillate after distillation pretreatment, add it to a 50mL colorimetric tube, add a certain amount of 1mol·L-1 sodium hydroxide solution to neutralize the boric acid, and dilute to the marked line. Add 1.5mL of Nessler's reagent and mix well. After standing for 10 min, measure the absorbance with the standard curve steps. ④Blank test: Replace the water sample with ammonia-free water, and do the blank measurement of the whole procedure.
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