Distillation and Absorption of Inorganic Nitrogen Standard Samples

The nitrogen determination process is relatively complex, and generally includes the digestion process completed in the digester, the distillation process completed in the distillation apparatus, and four steps such as titration and calculation. Therefore, it is best for beginners to use a separate experiment for each process so that they can master each process and then operate it. In order to familiarize with the distillation and titration operation techniques, beginners should first practice repeated tests with inorganic nitrogen standard samples, and then determine unknown organic nitrogen samples. Ammonium sulfate is usually tested three times with known concentrations.

Take five clean 100mL Erlenmeyer flasks, followed by 2% boric acid solution 20mL, methylene blue - methyl red mixed indicator (purple-red) 3 to 4 drops, cover the bottle ready for use. Take one of the Erlenmeyer flasks to receive the lower end of the condenser tube and immerse the outlet of the condenser tube in the solution. Note: The collector piston must be opened before this operation to prevent the liquid in the conical flask from sucking back. Accurately draw 2mL of ammonium sulfate standard solution into the glass cup, carefully lift the rod-shaped glass plug to slowly flow the ammonium sulfate solution into the distiller bottle, rinse the small glass cup with small amount of distilled water 3 times, and place it in a decanter. Then add 10 mL of 30% NaOH solution to the small glass bulb in the measuring cylinder and let the alkali solution slowly flow into the distillation flask. When the alkali solution has not completely flowed in, place the rod-like glass stopper tightly. About 5 mL of distilled water is added to the small glass bulb, and the glass stopper is slowly opened, so that half of the water flows into the distillation flask and half of the water remains in the small glass bulb as a water seal. The collector piston is closed and the steam generator is heated and distilled. The boric acid-indicator mixture in the Erlenmeyer flask changes from magenta to green due to the absorption of ammonia. From the time of discoloration, distill 3~5min, move the conical flask so that the liquid level in the bottle is about 1cm away from the lower end of the condensing tube, and rinse the lower end of the condensing tube with a small amount of distilled water. Continue distilling for another 1min. Remove the Erlenmeyer flask and cover it. Prepare for titration.

After the distillation is completed, remove the gas lamp, clamp the rubber tube between the steam generator and the collector, and remove the waste liquid after reaction. Rinse the small glass cup several times with water and remove the waste solution. After repeated rinsing, the next sample can be distilled. Repeat with standard ammonium sulfate twice as above. Another 2 mL of distilled water was used instead of standard ammonium sulfate for blank determination twice. The distilled flasks were titrated together.