High Performance Liquid Chromatography–Size Exclusion Chromatography for Rapid Analysis of Total Polar Compounds in Used Frying Oils

Abstract

AbstractAnalysis of used frying oil samples by high performance liquid chromatography–size exclusion chromatography (HPLC–SEC or HPSEC) was compared to AOCS Official Method Cd 20‐91 (silica gel column chromatography) for the purpose of developing a rapid analysis of total polar compounds (TPC). In a direct comparison of the two analytical methods using four different sets of used frying oils (21 total oil samples) ranging from fresh to discard quality (4.3 to 35.4% TPC by column chromatography), the weight percent total polar compounds (%TPC) determined by HPLC–SEC averaged 0.71% higher than the values by silica gel column chromatography. Reproducibility of the HPLC–SEC method of sr = 0.30 and RSDr% = 1.22 compares to the variability of sr = 0.29 and RSDr = 1.3 for samples of approximately the same %TPC, reported in AOCS Method Cd 20‐91. Because the rapid method does not separate pure (non‐polar) triacylglycerol (TAG) and polar, oxidized TAG (OX‐TAG), a high concentration of OX‐TAG will quantitatively affect the results. This places practical limits on the types of studies to which the method may be applied if a separate analysis for the OX‐TAG is not performed. Advantages of the HPLC–SEC method include the following. It uses about 75% less solvent than standard column chromatography methods for determination of %TPC. This HPLC–SEC method is very similar to AOCS Official Method Cd 22‐91, and thus, also separates and quantifies polymerized triacylglycerols. The HPLC–SEC method determines both TAG polymer concentration and %TPC of used frying oils in about 1 h.