The
determination of metals in petroleum derivates is an important
issue related to quality control of these products. Therefore, we
conducted a research work to propose a simple strategy for the extraction
of Mg, Mn, and Zn from Brazilian automotive gasoline, which contains
ethyl alcohol, and followed their quantification by flame atomic absorption
spectrometry (FAAS). The extraction method consisted of two steps.
In the first step, we formed a microemulsion with the gasoline sample
and the acid extractant solution using 1-propyl alcohol as the dispersant
agent. Afterward, we induced microemulsion breaking with addition
of water, yielding two immiscible phases: (i) a gasoline phase on
top, and (ii) a water/alcohol acid solution at the bottom. Mg, Mn,
and Zn extracted from the sample were in the bottom phase. The water/alcohol
phase was collected for the determination of the analytes by FAAS.
The experimental parameters of the method were optimized, as well
as the calibration conditions. Under optimum conditions, we dispersed
100 μL of the extractant solution (3.5 mol L–1 HNO3) through the sample (9.20 mL) using 700 μL
of 1-propyl alcohol. After that, we induced microemulsion breakdown
with 300–600 μL of deionized water, depending on the
analyte. The extracts (bottom phase) were collected and analyzed using
a matrix-matching strategy, and the adjustment of the nebulizer aspiration
flow rate was shown to be very important to achieve satisfactory accuracy.
The method presented the following limits of detection: 0.02, 0.03,
and 0.03 mg L–1 for Mg, Mn, and Zn, respectively,
and the limits of quantification of 0.05, 0.1, and 0.09 mg L–1, respectively. Five samples of Brazilian gasoline were tested using
the developed method, yielding concentrations of Mg, Mn, and Zn between
0 and 0.05, 0.11 and 0.17, and 0.22 and 0.46 mg L–1, respectively. The analysis of spiked samples was carried out to
evaluate the method accuracy, and recovery percentages between 90
and 120% were verified.