The developed method (DM) allows to perform experiments in shorter time with reduced amount of sample and reagent for fatty acids (FA) determination in fermented milk samples. Design Expert software was employed to discover the greatest sonication time (7 and 20 min) and concentration for alkaline and acidic reactions (0.70 and 1.5 mol L-1). Validation procedures were applied in yogurt samples with diverse fat content, ranging from 1.22 to 2.83%, being in agreement with acceptable values. Besides, the intraday relative standard deviation (RSD) (1.86%) and interday RSD (4.23%) values confirmed the good accuracy of the proposed method for FA derivatization.

This work proposed a novel, relatively low-cost and rapid analytical method using microemulsion as sample preparation to determine iron (Fe) in vegetable oils by flame atomic absorption spectrometry technique (FAAS). The vegetable oil microemulsions were obtained by mixing appropriate proportions of the crude and refined vegetable oil, Triton® X-100, 1-propanol and nitric acid 50% (v v-1). Moreover, an external calibration method was established using aqueous Fe standards instead of expensive and unstable organometallic standards. The limits of detection and quantification were 0.40 and 1.3 mg kg-1 of oil, respectively. The accuracy was checked by recovery studies (with recoveries ranging 84-105%) and by Fe determination in digested vegetable oil samples by inductively coupled plasma optical emission spectrometry (ICP OES) as comparative procedure. The proposed analytical method was efficient to determine Fe in crude and refined vegetable oils from various vegetable sources, besides being suitable for routine analyses due to its simplicity.