BUCHI Extraction System B-811 LSV - Manual (Page 23)

4 Description of function
23 B-811 Operation Manual, Version G
Hot Extraction
In case of a “Hot Extraction” the sample is placed in the boiling solvent and extracted. This method is
also know as Randall or Goldfisch extraction.
The solvent is heated up by the lower heating element and evaporated. The vapor rises up to the •
condenser. The condensed solvent flows down along the condensation tube into the extraction
chamber with the sample inside. The condensed solvent is collected in the extraction chamber
while the glass valve is closed. The sample is extracted.
The solvent level rises up to the optical sensor.
•
Each time the solvent level reaches the optical sensor, the glass valves opens for a short time and •
a few milliliters of hot solvent containing the extracted compounds are drained into the beaker.
After the first drain happened the upper heating element is activated and the solvent in the extrac-
tion chamber is warmed up. The extraction efficiency is improved because an exchange of fresh
and used solvent is constantly given.
During the extraction process the solvent level remains close to the detection line of the optical
•
sensor.
When the programmed extraction time is up, all valves are opened and the solvent is released into the
beaker. The upper heating element is turned off. Then the program switches to the next step.
1
3
2
a Upper heating element activated
b Lower heating element activated
c Solvent level remains at the height of the optical sensor
Fig. 4.8: Procedure of Hot Extraction
Continuous Flow
The method “Continuous Flow” is also known as Twisselmann extraction. The method is a washing up
under controlled conditions.
The solvent is heated up by the lower heating element and evaporated. •
The vapor rises up to the condenser. The condensed solvent flows down along the condensation •
tube through the sample into the beaker. During the entire extraction process the glass valve is
open. The optical sensor is deactivated. The sample is rinsed efficiently.
When the programmed time is up, the solvent is in the beaker and the program switches to the next
step.