A fast method based on reversed-phase ultra-high-performance liquid chromatography using evaporative light scattering detection (RP-UHPLC-ELSD) was developed for monitoring the intermediates and end products of biodiesel production. Gradient elution of water, acetonitrile, and a mixture of acetonitrile:2-propanol:n-hexane was used. With a minimal and easy sample preparation, fatty acid methyl esters (FAME), fatty acid ethyl esters (FAEE), free fatty acids (FFA), monoacylglycerols (MAG), diacylglycerols (DAG), and triacylglycerols (TAG) were successfully separated. The developed method was used to monitor an ethylic enzymatic transesterification of soybean oil and to characterize the ester content of methyl and ethyl biodiesel. The ester content obtained was compared with the reference method by gas chromatography and flame ionization detector (GC-FID), with similar results for both methyl and ethyl biodiesel. The presented method is a simple and fast alternative, a 17 min run, to monitor the transesterification process, simultaneously quantifying all the analytes produced in the reaction: biodiesel and its intermediates. Limits of detection (LOD, between 29 and 307 ng) and quantification (LOQ, between 48 and 614 ng), linearity (R2>0.99), precision (between 0.30 and 6.58%), and accuracy (between 81.6 and 119.9%) were determined for the twenty-one compounds.
Keywords: Acylglycerol; Biodiesel; ELSD; Ester; Free fatty acid; UHPLC.
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