Chemistry Reference
In-Depth Information
100
V(IV)
V (V)
V (Total)
80
60
40
20
0
Sample 1
Sample 2
Sample 3
Vanadium species
Figure 3.6
Vanadium speciation in natural water.
functionalized resin can be used as a good sorbent for preconcentration and determination of vanadium
species at trace levels. The method is simple, low cost, easy to handle and environmentally benign.
3.2.2.4
Solventfree extraction of essential oils
During the last two and a half decades, solventfree extraction methods have been introduced or rediscovered,
forced not only by the concern and/or cost associated with extensive solvent use but also by the new
opportunities offered by green devices. Microwave-assisted extraction has been proved to be effectively
applicable for extractions from difficult sample matrices, previously treated by longer time and solvent
intensive Soxhlet extractions and hydrodistillations. Solventfree microwave extraction (SFME) apparatus is
a combination of microwave heating and dry distillation at atmospheric pressure. SFME has been successfully
introduced for laboratory scale applications in the extraction of essential oils from different kinds of aromatic
plants. The method for extracting natural products without using any solvent and using microwave energy has
been reported in 2003 [18].
Green laboratory proposal
[19]
SFME was performed in a Milestone DryDist microwave laboratory oven
working at a frequency of 2455 MHz with a maximum power of 1000 W. The dimensions of the PTFE-coated
cavity are 35 cm × 35 cm × 35 cm. During such experiments, time, temperature, pressure and power can be
controlled.
In a typical SFME procedure (Figure 3.7) performed at atmospheric pressure, 250 g of fresh plant materials
were heated using a fixed power 500 W for 30 min without adding any solvent or water. A cooling system
outside the microwave cavity condensed the distillate continuously. Condensed water was refluxed to the
extraction vessel in order to provide uniform conditions of temperature and humidity for extraction. The
extraction was continued at 100
C until no more essential oil was obtained. The essential oil was collected,
dried under anhydrous Na
2
SO
4
and stored at 0
°
°
C until further use.
Comments
SFME has been compared with the conventional hydrodistillation technique for the extraction
of essential oil from three herbs; basil (
Ocimum basilicum L
.), garden mint (
Mentha crispa L.
) and thyme
