Direct Determination of Oleic Acid in Soybean Oil by Capacitively Coupled Contactless Conductivity Detection Capillary Electrophoresis in an Oil-Miscible KOH/1-Propanol/Methanol Medium

Wolmir José Böckel,Yara Patrícia Da Silva,Guillermo Ramis-Ramos,Clarisse M S Piatnicki,Ernesto F Simó-Alfonso,Carla R B Mendonça

doi:10.5935/0103-5053.20140155

Wolmir José Böckel, Yara Patrícia Da Silva + Show 4 more

Open Access

https://doi.org/10.5935/0103-5053.20140155

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Abstract

The aim of this work was to develop a quick direct analytical technique for the determination of oleic acid content in soybean oil by non-aqueous capillary electrophoresis with capacitively coupled contactless conductivity detection. The oil-miscible background electrolyte was a mixture of methanol/1-propanol (1:6 v/v) containing 4 × 10-2 mol L-1 KOH and 10% (v/v) ethylene glycol. Samples of 50 g L-1 soybean oil were prepared directly in the background electrolyte added with 1.33 × 10-3 g L-1 of salicylic acid as internal standard. Quantitative tests were performed by adding to the samples pure oleic acid in the range from 0.53 to 2.13 × 10-3 mol L-1. Under negative polarity anionic solutes moved faster than the electro-osmotic flow so that oleic acid was detected in 16 minutes. The limits of detection and quantification were, respectively, 24 and 81 µmol L-1. Such results demonstrate that, unlike required by other methods, low levels of oleic acid can be quantitatively determined in soybean oil without prior extraction.

Highlights

It is well known that fats and oils decompose slowly during storage releasing their fatty acid (FA) constituents
In Brazil, since synthesis of biodiesel is heavily dependent on the production of soybean oil, quality control parameters, such as free fatty acid content in the feedstock, is imperative
The present study aims to evidence the advantages of associating non-aqueous capillary electrophoresis (NACE) and capacitively coupled contactless conductivity detectors in the direct quantification of oleic acid, a monounsaturated fatty acid (C18H34O2), in soybean oil

Summary

Introduction

It is well known that fats and oils decompose slowly during storage releasing their fatty acid (FA) constituents. A quality and freshness assessment of fats and oils can be made based on the fatty acid content. Important interests in oleic acid determination are, among others, medical research, biotechnology and evaluation of the lipid distribution in foods.[1,2,3,4] In Brazil, since synthesis of biodiesel is heavily dependent on the production of soybean oil, quality control parameters, such as free fatty acid content in the feedstock, is imperative. Development of fast, reproducible and low cost methods for the determination of fatty acids is a target of great interest.

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