water phase and to enhance the contact area between sample and solvent. A huge
contact area improves the extraction speed and leads to a fast adjustment of steadystate conditions and sufficient extraction yield. After shaking the different phases can
be easily separated and the organic layer can be collected. The application is suitable
to run twice or in multiple steps. In this case, usage of different solvents as well as
treatment of the water phase prior to extraction (e.g. change of pH, addition of salt)
can extend the spectra of extracted substances enormously.
An obvious prerequisite for a successful extraction with this technique is the
formation of separated phases, that means water and solvent shall not be mixable. In
Fig. 3.3 a clear discrimination between miscible and non-miscible solvents is
marked. This aspect restricts the selection of appropriate solvents, since more
polar solvents (miscible with water) are not appropriate. As a consequence, ideal
extractants for more polar substances (that means more polar solvents) are not
suitable and the extraction yield will not be optimal.
Extraction by shaking exhibits the advantage of short extraction times (only a few
minutes per extraction step) but the disadvantage of intensive personnel expenses
and higher risk of lower reproducibility. A second technique is more automated, the
perforator according to Kutscher and Steudel. A scheme is given in Fig. 3.5. Here a
continuous extraction is achieved by dropwise penetration of the water sample with
organic solvents. For this purpose, the extraction solvent is boiled in a receiver and
the vapor is condensed into a system that allows to release very fine bubbles at the
bottom of the water sample moving upwards. The solvent containing the extracted
substances gets collected above the water sample and runs back to the receiver.
This technique can be run automatically but needs an elevated runtime of a couple
of days (commonly between 48 and 96 h). Here, also the solvent can be changed
during the extraction for extending the spectra of extracted analytes. However, one
Organic phase
Aqueous phase
Before
During
Af ter shaking
Analytes
Fig. 3.4 A simple liquid/liquid extraction technique, shaking assisted extraction in a separatory
funnel
3.2 Extraction
21
contact area improves the extraction speed and leads to a fast adjustment of steadystate conditions and sufficient extraction yield. After shaking the different phases can
be easily separated and the organic layer can be collected. The application is suitable
to run twice or in multiple steps. In this case, usage of different solvents as well as
treatment of the water phase prior to extraction (e.g. change of pH, addition of salt)
can extend the spectra of extracted substances enormously.
An obvious prerequisite for a successful extraction with this technique is the
formation of separated phases, that means water and solvent shall not be mixable. In
Fig. 3.3 a clear discrimination between miscible and non-miscible solvents is
marked. This aspect restricts the selection of appropriate solvents, since more
polar solvents (miscible with water) are not appropriate. As a consequence, ideal
extractants for more polar substances (that means more polar solvents) are not
suitable and the extraction yield will not be optimal.
Extraction by shaking exhibits the advantage of short extraction times (only a few
minutes per extraction step) but the disadvantage of intensive personnel expenses
and higher risk of lower reproducibility. A second technique is more automated, the
perforator according to Kutscher and Steudel. A scheme is given in Fig. 3.5. Here a
continuous extraction is achieved by dropwise penetration of the water sample with
organic solvents. For this purpose, the extraction solvent is boiled in a receiver and
the vapor is condensed into a system that allows to release very fine bubbles at the
bottom of the water sample moving upwards. The solvent containing the extracted
substances gets collected above the water sample and runs back to the receiver.
This technique can be run automatically but needs an elevated runtime of a couple
of days (commonly between 48 and 96 h). Here, also the solvent can be changed
during the extraction for extending the spectra of extracted analytes. However, one
Organic phase
Aqueous phase
Before
During
Af ter shaking
Analytes
Fig. 3.4 A simple liquid/liquid extraction technique, shaking assisted extraction in a separatory
funnel
3.2 Extraction
21