Buchi K-350, Руководство по эксплуатации

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6 Operation
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K-350
Operation Manual, Version G
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 2-3 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:
32 %. Add alkali to the sample in a ratio of about 1 part of acid to 3 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.