3.3. Stability study
The analyte stability in the biodiesel microemulsion was monitored
for Na, K, Ca, and Mg for a period of 15 days. The same stability study
with xylene dilution was evaluated for comparison for a period of
6 hours. The samples were prepared as described before (Sections 2.3
and 2.4).
The results (Fig. 1) have shown a significant decrease in analyte
signal (38% for Na, 66% for K, 22% for Ca, and 62% for Mg) when the
sample was prepared through xylene dilution in a short period of time
(6 h). This decrease can be explained by the metal adsorption in the
recipient walls [34]. This fact is not convenient because it can cause
erroneous analytical results, affecting the accuracy of the method.
In contrast to this, a good stability was obtained for analyte signals
in the samples as microemulsion for a long time (15 days) (Fig. 2),
which indicates that the proposed procedure for sample preparation
is more advantageous than the xylene dilution.