A rapid method for determination of polar compounds in used frying fats and oils

The determination of polar compounds by adsorption chromatography is the most accepted method for the analysis of used frying fats due to its high precision and accuracy. However, this method is expensive and time consuming. In this study, a rapid analytical method to determine polar compounds is proposed. Starting from milligrams of sample dissolved in a solution of hexane containing methyl oleate as internal standard, the nonpolar fraction, which comprises the non-altered triglycerides (TG) and the internal standard, is obtained by solid phase extraction. Then, the non polar fraction is quantitatively analyzed in 15 min by high-performance size-exclusion chromatography (HPSEC) and the polar fraction is determined by difference of weight. Response factors for pure TG and FAME were calculated. Six samples of sunflower oils of different degrees of unsaturation were analyzed in triplicate and the results were compared with those obtained by the gravimetric method based on silica classical column chromatography. Results showed no significant differences between the two methods. In addition, the repeatability of the proposed method was excellent, as the coefficient of variation ranged from 1.5 to 13% depending on the contents of polar compounds.