2.3. Procedures
For the CPE, aliquots of 10 ml of a solution containing the
analytes, 2.0 g L−1 Triton X-100 and 1.0 × 10−3 M PMBP
buffered at a suitable pH were kept in the thermostatic bath
maintained at 80 ◦C for 25 min. Since the surfactant density
is 1.07 g ml−1 therefore, the surfactant-rich phase can settle
through the aqueous phase. The phase separation was accelerated
by centrifuging for 5 min at 3000 rpm. After cooling in an
ice-bath, the surfactant-rich phase became viscous and was retained
at the bottom of the tube. The aqueous phases can readily
be discarded simply by inverting the tube. To decrease the viscosity
of the extract and allow its pipetting, 200 μl of 0.1 M
HNO3 was added to the surfactant-rich phase. 20 μl sample
was introduced into the GFAAS by manual injection. Calibration was performed against aqueous standards submitted to the
same cloud point extraction procedure. A blank submitted to
the same procedure described above was measured parallel to
the samples and calibration solutions.