Documentation:Standard Operating Procedures for Buchi Digestion and Distillation system

From UBC Wiki
Please obtain proper training from the FNH teaching lab technician Imelda Cheung (Imelda.Cheung@ubc.ca) prior to using the Buchi digestion and distillation system.
Digestion Procedures
  1. To set up, move the digestion unit into the fume hood carefully and plug into the 220 V plug (note it is a special voltage).
  2. Turn on the machine by pressing the start button once and the display should read 400oC.
    It will take 2 hours to warm up in the fume hood, with the unit covered with aluminum foil. If the unit is not covered, it may take up to 7 hours to reach digestion temperature.
  3. While the machine is warming up, prepare your samples.
    Regardless of the number of samples being run, all sample tubes should be placed in the rack. The sample tubes could be left empty if necessary.
  4. Precisely weigh 1 g of sample, tiny amount of boiling chips, 1 Kjeldahl tablet and 20 ml concentrated sulfuric acid into the tube (perform in triplicate). Blank should also be performed without the addition of samples.
    Concentrated sulfuric acid should be added in the fume hood and handled with care.
  5. Place all sample tubes in the rack, be sure to place the shelf/holder in to secure all tubes.
    Without the shelf/holder, all tubes will fall out of the rack if lifted.
  6. When the digestion unit has reached the set temperature, place the tubes in the rack into the unit.
  7. Lift to release the top seal of the unit, and place over top of sample tubes to ensure a tight seal.
  8. Ensure the exhaust tube is placed inside the Erlenmeyer flask beside the unit.
  9. Press the START button to begin digestion. The time display should read 120 min.
  10. When the time is up, system immediately cool and the “heat” light will start flashing.
  11. Let unit cool overnight in the fume hood and proceed to Distillation Procedures the next day.
  12. If the whole procedures must be carried out within the same day (not recommended), very carefully move the sample tube rack up to the cooling position (there is a location on the system to hang the rack for cooling).
    The sample tube rack that is fully loaded is very heavy to lift. Make sure you have practiced this motion with the cool rack a few times prior to attempting it after the digestion. Also, since the sample tubes are at 400oC, any clinking of the sample tube may result in a crack in the tube. A cracked sample tube cannot be used since there will be a high chance of the tube breaking during the high heat.
  13. Do NOT turn off system until “heat” light stops and goes off (this may take hours).
  14. Now the system can be turned off and unplugged.


Distillation Procedures
  1. Plug in the BUCHI distillation unit K-350 to the 220V plug.
    There is only one 220V plug so you cannot operate both the digestion unit and distillation unit at the same time.
  2. Turn on the distillation unit and warm up for 10 min.
  3. Ensure both reagent tubes are placed in the reagent bottles (one in ddwater and the other in 32% NaOH) and that both reagent bottles contain sufficient solutions for your experiments.
  4. Turn on water for condenser tube.
    The water tap is controlled by the distillation unit so it is normal you do not see water solely by turning on the tap without the unit being in used. However, while the unit is running, you should see water running through the condenser.
  5. Before performing the distillation of sample, place the discard tube in, secure and close the shield door, then press “reagent” button to run 200 ml of 32% NaOH into the system to rinse out ddH2O left in the tubing.
  6. Replace discard tube with sample tube, secure and close the shield door, then press “reagent” button until the sample tube has liquid reaching just below the 200 ml mark (marked by black line).
  7. In a 500 ml Erlenmeyer flask, place gently more than the estimated volume of standardized 0.5 N HCl. If you estimated 23 ml of 0.5 N HCl is needed, use 25 ml.
  8. Add ddH2O in the Erlenmeyer flask such that the water level reaches about 100 ml (or until the outlet tube of the distillation unit can submerge in the liquid).
    You can put a box underneath the Erlenmeyer flask such that the tubing can be submerged in the liquid without adding excessive amount of ddwater.
  9. Add a few drops of methyl red to the Erlenmeyer flask.
  10. Place the Erlenmeyer flask in the distillation unit and place the tubing in the flask, ensuring the tube is submerged in the solution. Add more ddH2O if needed.
  11. Press “Start” and the procedure should be completed in 4 – 5 min.
  12. When the distillation is complete, remove the Erlenmeyer flask and titrate against standardized NaOH solution (purchased from Fisher) until the end point (from pink to orange) is reached.
  13. When all the distillation is complete, place the NaOH tube of the distillation system into a beaker of 1000 ml ddH2O, press “reagent” to rinse the system out of NaOH.
    At the end of the day, no NaOH should remain in the system or else clogging will occur.
  14. The distillation unit can now be turned off and unplugged.
  15. Wash all used glassware and return them where you have found them.
To reserve a time to utilize the BUCHI digestion and distillation system, please visit https://www.qreserve.com/r/resource/QR00182775