Evaporative light scattering detector in normal-phase high-performance liquid chromatography determination of FAME oxidation products

The use of an ELS detector in NP-HPLC for quantitative analysis of oxidation products in FAME obtained from oils is evaluated in this study. The results obtained have shown that the ELS detector enables the quantitative determination of the hydroperoxides of oleic and linoleic acid methyl esters as a whole, and connected in series with a UV detector makes it possible to determine both groups of compounds by difference, providing useful complementary information. The limits of detection (LOD) and quantification (LOQ) found for hydroperoxides were respectively 2.5 and 5.7 μg mL−1 and precision of quantitation expressed as coefficient of variation was lower than 10%. Due to a low sensitivity the ELS detector shows limitations to determine the low contents of secondary oxidation products in the direct analysis of FAME oxidized at low or moderate temperature. Analysis of FAME samples obtained either from high linoleic sunflower oil (HLSO) or high oleic sunflower oil (HOSO) and oxidized at 80 °C showed that only ketodienes formed from methyl linoleate can be determined in samples with relatively high oxidation, being the LOD and LOQ 0.2 and 0.4 mg/g FAME, respectively, at the analytical conditions applied. The ELS detector also enabled the determination of methyl cis-9,10-epoxystearate and methyl trans-9,10-epoxystearate, which were resolved at the chromatographic conditions applied. Results showed that these compounds, which are formed from methyl oleate, were not detected in the high-linoleic sample, but occurred at non-negligible levels in the oxidized FAME obtained from HOSO.

► Coupling of ELS in NP-HPLC–UV provides useful complementary analytical information in the analysis of FAME oxidation products.
► Quantitative analysis of hydroperoxides of linoleic and oleic acid in oxidized samples of FAME.
► Quantitative analysis of monoepoxides formed from oleic acid methyl ester by NP-HPLC-ELS.
► Formation of monoepoxides at moderate temperature (80 °C) at levels of mg/g in FAME derived from monounsaturated oils.
► Detection of monoepoxides in lipids is an indication of significant oxidation of oleic acid.