Buchi K-437, Руководство по эксплуатации, Страница: 19 / 34

6 Operation
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K-437 Operation Manual, Version A
6 .2 Kjeldahl digestion process
ATTENTION
Do not use cold water to cool down hot digestion tubes after digestion. The resulting temperature •
shock might lead to tensions in the glass.
Make sure that the 20 place rack containing the digestion tubes is placed in and removed from
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the digestion block with reasonable care.
Do not use glass beads. If the sample tends to boiling delays, use digestion rods, which are
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gentler for the glass tubes.
To carry out a Kjeldahl digestion, proceed as follows:
Switch the instrument on and preheat it to the required temperature. •
Place the digestion tubes into the rack. •
Pour the samples and reagents into the digestion tubes. •
Fit sealing covers over any vacant rack positions. •
Fit the sample rack into the fixture provided. •
Mount the suction unit, with the seals fitted, onto the digestion tubes. •
When the digestion temperature is reached (READY appears on the display) fit the sample rack, •
with the suction unit fitted, into the heating block and press the START button. (The connected
Scrubber will start automatically.)
Start up the Scrubber or water jet pump before gases can develop.
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After the digestion process is finished, put the sample rack into the cooling position, with the •
suction unit fitted, so that it can cool down.
When the cooling procedure is finished, press the STOP button to end the digestion process. The
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connected Scrubber will switch off.
The blinking LED “HEATING” indicates that the instrument is still hot and is being cooled by the
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ventilator. After the digestion is finished the instrument should remain connected to power for an
additional 30 minutes. Thus it is cooled and the service life of the built-in display is extended.
Repeat the procedure for additional digestion processes.
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6 .3 Operating the K-437
Switching on the K-437
420 120
Press the main switch. The switch lights up
green.
The temperature and digestion time last
selected are displayed.
Editing parameters
The inputs can be changed by pressing the TEMP or TIME buttons. Enter the required temperature or
time by pressing the arrow buttons and confirm by pressing ENTER. If “0” is entered for the time, the
timer will be switched off and the operator must observe the digestion time.