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guoyayun40

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1楼 2010-12-11 13:37:16

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Originally posted by guoyayun40 at 2010-12-13 21:36:50:

哪一个更重要一些呀？

The use of
micellar systems such as CPE for separation and preconcentration
has attracted considerable attention in the last few years mainly
because it is in agreement with the “green chemistry” principles.
Green chemistry can be defined as those procedures for decreasing
or eliminating the use or generation of toxic substances for human
health and for the environment [12]. CPE is a green method for the
following reasons: (a) it uses as an extractor media diluted solutions
of the surfactants that are inexpensive, resulting in the economy of
reagents and generation of few laboratory residues; and (b) surfactants
are not toxic, not volatile, and not easily flammable, unlike
organic solvents used in liquid–liquid extraction [13,14].
CPE consist of three simple steps: (1) solubilization of the analytes
in the micellar aggregates; (2) clouding; (3) phase separation
for analysis. When a surfactant solution is heated over a critical
temperature, the solution easily separates into two distinct phases:
one contains a surfactant at a concentration below, or equal to, a
critical micelle concentration; the other is a surfactant-rich phase.
The hydrophobic compounds initially present in the solution and
bound to the micelles are extracted to the surfactant-rich phase.
This phenomenon is observed, in particular, for polyoxyethylene
surfactants and can be attributed to the two ethylene oxide segments
in the micelle that repel each other at low temperature when
they are hydrated and attract each other when the temperature
increases owing to the dehydration.