BUCHI Distillation Unit K-355 - Manual (Page 24)

6 Operation
24 K-350 Operation Manual, Version F
6 .5 Carrying out a Kjeldahl distillation
To carry out a distillation, proceed as follows:
Switch on the instrument and wait until the steam generator is ready.
Insert the sample tube containing the sample diluted in water. The dilution with water prevents a
too violent reaction when subsequently adding the sodium hydroxide solution. The sample must be
diluted in a ratio of approximately 1 part of acid to 2 parts of water.
Prepare a conical flask or a similar receptacle with a volume of about 250 ml as receiving vessel.
Fill boric acid solution 4% and 2- drops of Sher indicator in the receiving vessel. Alternative:
Select suitable chemicals for the back titration.
Add sodium hydroxide solution by pressing “REAGENT“: Recommended alkali concentration:
2%. Add alkali to the sample in a ratio of about 1 part of acid to parts of sodium hydroxide
solution. The volume of the added sodium hydroxide solution is measured on the scale behind the
sample tube. The added volume selected must produce a clear shift in color to brown or blue.
Set the required distillation time.
Start the distillation by pressing “START”.
NOTE
After distillation or after “STOP“, the last distillation time can be recalled by pressing “START“ or will
automatically be recalled when exchanging the sample tube.
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