Microemulsion stability
Experiments were conducted to determine the minimum
amount of propan-1-ol required to form emulsions whose phases
did not separate within 3 h, which is an enough period to consider
the stability of the system and to realize the measurements in the
equipment. This test consisted of preparing microemulsions, after
which their stability was monitored by simple visual inspection
of the emulsion samples. In these experiments, the propan-1-ol
was tested in the range of 2 to 9 mL, using 0.5 g of vegetable oil
sample and 100 lL of hydrochloric acid. Water was added under
continuous agitation until a final volume of 10 mL. The results indicated
that only volumes of propan-1-ol higher than 8 mL produced
emulsions that remained homogeneous. Therefore, after the addition
of sample and hydrochloric acid aliquot, the final volume of
10 mL was completed with the alcohol, avoiding phase separation
when the absorbance measurements were performed.
Additionally, the stability of Cu, Fe, Ni and Zn concentrations in
the microemulsion were checked every 30 min, for 240 min. The
signal was stable during the monitoring time, indicating stability
of the analytes.
3.2. Analytical