Introduction to Soil Chemistry

136 extraction
Figure 7.3. Solutions obtained by Soxhlet and magnetic stirring of soil with either water or
hexane.
while the magnetic stirred extract is cloudy even after being filtered 2 times.
All three solutions have ultraviolet absorptions as a result of components
extracted from the soil [21].
7.4.3. Ultrasonic Extraction
Ultrasonic extraction or sonication involves disruption and mixing a sample
and extractant using ultrasound, which is sound above the hearing range of
approximately 10,000Hz. A high-frequency electrical current is applied to a
piezoelectric crystal that causes a metal tip attached to it to oscillate at high
frequency. This produces a series of compressions and relaxations in the
extraction mixture, causing disruption and mixing in the extraction vessel. A
typical ultrasonic “horn” is shown in Figure 7.4. A complete ultrasonic extraction
setup involves both the “horn” and a high-frequency source [7,22].
7.4.4. Microwave-Assisted Extraction
Caution: Microwave-assisted extraction must always and only be
carried out in microwave ovens and digestion containers, with appropriate
sensors, especially designed for this purpose.
Microwave-assisted extraction involves sealing a sample and extractant in a
special microwavable digestion container, placing it in a special microwave