Onthe other hand, the absorbance signal for inorganic standards and samples both prepared in the same way, i.e., as a threecomponent solution, did not change significantly over 2 days for magnesium and at least 4 days for calcium and zinc, as showed in Fig. 3. Higher stability for a number of elements in microemulsions have been reported in the literature [22,24,29], associated with the use of mineral acid. This high stability found in this work, together with the use of inorganic standard for calibration, make this sample preparation more suitable for routine application.