3.3. Exposure time
The effect of exposure time on extraction efficiency was evaluated
by spiking 5-g soil samples at 20 ng g−1 of the analytes.
Extraction times between 15 and 120 min at a stirring rate of
105 rad s−1 were evaluated. The extraction efficiency increased
with exposure time, and equilibrium was attained at >90 min
(Fig. 2). Thus, the extraction time for all subsequent experiments
was standardized at 90 min