Analysis of Unsaponifiable Compounds of Edible Oils by Automated On-Line Coupling Reversed-Phase Liquid Chromatography−Gas Chromatography Using the Through Oven Transfer Adsorption Desorption Interface

Abstract

An automated method for analysis of unsaponifiable compounds in edible oils is presented. The method involves the on-line coupling of reversed-phase liquid chromatography and gas chromatography (LC-GC) using the through oven transfer adsorption desorption (TOTAD) interface. The oil is injected directly with no sample pretreatment step other than filtration. It may also be considered to dilute the oil sample. In the LC step, a short C4 column using a methanol/water eluent separates analytes from the other components of the oils, which are made up of mainly triglycerides. A LC fraction of up to 1.6 mL containing the analytes is transferred to GC at a flow rate of 0.1-2 mL/min. The TOTAD interface allows solvent venting and the introduction of the analytes into the GC column. The proposed fully automated method allows the analysis of different groups of compounds (free sterols, tocopherols, squalene, and erythrodiol and uvaol) in one chromatographic run or the analysis of these compounds in different groups. Sensitivity is more than necessary, and repeatability is good, the CV ranging from 3 to 12% for the full analysis.

A new methodology capable of characterizing most volatile and less volatile minor edible oils components in a single chromatographic run without solvents or reagents. Detection of new components

“…The elimination of the saponification step has been proposed for the simultaneous direct determination of sterols, tocopherols and squalene by on-line coupling of liquid chromatography and capillary gas chromatography using different transfer and coupling techniques for the interfaces of the chromatographs requiring or not the dissolution of the oil in dichloromethane. These more recent methods have many advantages in relation to the prior ones (Cortés, Sanchez, Villén, & Vazquez, 2006;Grob, Lanfranchi, & Mariani, 1989, 1990). …”

Analysis of free and esterified sterols in edible oils by online reversed phase liquid chromatography–gas chromatography (RPLC–GC) using the through oven transfer adsorption desorption (TOTAD) interface

“…This allows the minor components to be isolated from the rest of the sample, primarily the triglycerides, and to be transferred online to the GC, where the analysis is carried out. In our previous work using the TOTAD interface (Cortés et al, 2006); the RPLC conditions enabled isolation of the sterols, together with tocopherols, from the triglycerides to be transferred to the GC. Nevertheless, in this case the analysed sterols corresponded only to free sterols.…”

“…However, with this procedure it is not possible to automate the system. The use of the Through Oven Transfer Adsorption Desorption (TOTAD) interface for the online coupled reversed phase liquid chromatography-gas chromatography (RPLC-GC) (Cortés, Sánchez, Villén, & Vázquez, 2006) avoids this problem. The TOTAD interface operation mode has been described previously (Alario, Pérez, Vázquez, & Villén, 2001;Pérez, Alario, Vázquez, & Villén, 1999.…”

“…The method includes a modification of that developed by Cortés et al (2006) to analyse free sterols and the use of saponification to release the esterified sterols, prior to RPLC-GC to analyse total sterols.…”

Analysis of wax esters in edible oils by automated on-line coupling liquid chromatography–gas chromatography using the through oven transfer adsorption desorption (TOTAD) interface

“…The interface is a modified PTV injector. The changes made in the PTV injector affect the pneumatics, sample introduction and solvent elimination and allows the large volume injection (LVI) of polar solvents [13,14] and the on-line coupling RPLC-GC [15][16][17]. The TOTAD interface has also been used for LVI of non-polar solvent in GC [18] but, up to date, it has not been used for NPLC-GC coupling.…”