For the formation of the homogeneous system it was necessary the use of a small amount of AVK in order to reduce the viscosity of lubricating oils. The n-propanol alcohol was chosen because its solubility in water is 100% [28]. A system based on oil-in-water (o/w) microemulsion, mainly with a large amount of water, is very advantageous in order to reduce the costs and because it is similar to aqueous solutions, beingmuchsimpler to obtain optimized instrument parameters for analysis without drastic changes after aqueous solutions analysis. It also allows the acidification of the system to increase the stability of the analytes in the solution. Calibration against aqueous standards may also be expected. Therefore, we tried first to use large amount of water to obtain
a microemulsion, but the hydrophobic phase (lubricating oil/AVK,
fixed ratio 1:15 in mass) not exceeding 2% in mass was not stabilized
when more than 20% in mass of water was used and the
emulsion formation was achieved.