Buchi K-437, Руководство по эксплуатации

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6 Operation
18
K-437 Operation Manual, Version A
6 Operation
This chapter gives examples of typical instrument applications and instructions on how to operate the
instrument properly and safely.
WARNING
Risk of injury.
Never operate the instrument when glassware is damaged. •
ATTENTION
Switch on the K-437 before a connected instrument produces gases.
6 .1 General information
The condensation zone of the sulphuric acid must not rise too high in the digestion tube (maximum of
5 cm below the rim of the tube).
Normally 18 - 20 ml of H
2
SO
4
is used for a weighed portion of approx. 1 g of organic material. For
weighed portions over and above this, approx. 3 - 5 ml of H
2
SO
4
(5 - 10 ml for greases and mineral
oils) must be used additionally for each additional gram of organic material.
WARNING
A rack filled with sample tubes and samples is heavy. Please consider the weight before transport.
ATTENTION
Hot, caustic sulfuric acid is used for the operation of the instrument. For this reason, personal protec-
tive equipment must be worn at all times when using this instrument or working in its immediate
proximity.
Close unused connections with glass caps.
It is absolutely essential that the seals on the suction pipes be properly installed and fit the glass
evenly.
To vaporize larger amounts of water (> 10 ml), it is advisable to use digestion rods as this will prevent
boiling delays. If the distillation temperature is too high, it is likely to cause substantial boiling delays.
The starting temperature should not be higher than 250 °C.
The digestion time depends on the substance to be digested. Information on this can be found in the
BUCHI application notes. If no BUCHI application is available, the digestion time must be ascertained
by means of experiments. (Once the solution has become clear, continue to boil the solution for about
30 minutes.) Once the samples have cooled off, the digestion tube can be connected directly to a
BUCHI distillation unit for distillation.
Due to different contact surfaces between the digestion tubes and the heating block, not all 20
samples boil simultaneously. However, as long as it is ensured that the digestion time and digestion
temperatures are sufficient, the different boiling times have no influence on the results.
If the digested samples are allowed to cool off for a long period of time, the samples might solidify
occasionally.
In this case, the sample must be liquefied again before it can be distilled:
by carefully adding a small quantity of distilled water, or •
by slightly warming it up in the Digest System. •