  We address a novel method for analytical determinations that combines
simplicity, rapidity, low consumption of chemicals, and portability with high
analytical performance taking into account parameters such as precision,
linearity, robustness, and accuracy. This approach relies on the effect of the
analyte content over the Gibbs free energy of dispersions, affecting the
thermodynamic stabilization of emulsions or Winsor systems to form
microemulsions (MEs). Such phenomenon was expressed by the minimum volume
fraction of amphiphile required to form microemulsion, which was the analytical
signal of the method. The performed studies were: phase behavior, droplet
dimension by dynamic light scattering, analytical curve, and robustness tests.
The reliability of the method was evaluated by determining water in ethanol
fuels and monoethylene glycol in complex samples of liquefied natural gas. The
dispersions were composed of water-chlorobenzene (water analysis) and
water-oleic acid (monoethylene glycol analysis) with ethanol as the hydrotrope
phase. The experiments to determine water demonstrated that the analytical
performance depends on the composition of ME. The linear range was fairly broad
with limits of linearity up to 70.00% water in ethanol. For monoethylene glycol
in water the linear range was observed throughout the volume fraction of
analyte. The natural gas samples provided by the Petrobras exhibited color,
particulate material, high ionic strength, and diverse compounds as metals,
carboxylic acids, and anions. The method allowed accurate measures bypassing
steps such as extraction, preconcentration, and dilution of the sample. In
addition, the levels of robustness were promising. This parameter was evaluated
by investigating the effect of (i) deviations in volumetric preparation of the
dispersions and (ii) changes in temperature over the analyte contents recorded
by the method.
