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.