Introduction to Soil Chemistry

extraction procedures 137
Figure 7.4. Ultrasonic “horn” for disruption and extraction of soil samples.
oven, and microwaving for the designated time period. Microwaves heat the
sample with consequent increase in container pressure, both of which decrease
the time needed for and increase the efficiency of extraction. Both temperature
and pressure are monitored and can be controlled during microwaveassisted
extraction. Because high temperature and pressure are produced, it is
essential that both the containers and microwave be designed specially for this
process.A microwave assisted microwave and extraction containers are shown
in Figure 7.5 [8,21,23,24].
7.4.5. Supercritical Extraction
Supercritical fluid extraction (SFE) involves extracting a material using carbon
dioxide maintained as a supercritical fluid. To do this, the carbon dioxide must
be kept above its critical temperature and pressure such that it is maintained
in its liquid state (liquid CO 2) during the extraction process, for example,
350atm and 80°C. A soil sample is placed in an extraction vessel that can be
maintained at the necessary pressure, and liquid CO2 is passed through the
soil and into a collection container. In some cases additives may be introduced