Capillary electrophoresis with capacitively coupled contactless conductivity detection for the determination of cis/trans isomers of octadec-9-enoic acid and other long chain fatty acids

Abstract

A capillary electrophoresis (CE)–capacitively coupled contactless conductivity detection (C4D) method for the simultaneous separation of eleven underivatized fatty acids (FAs), namely, lauric, myristic, tridecanoic (internal standard), pentadecanoic, palmitic, stearic, oleic, elaidic, linoleic, linolenic and arachidic acids is described. The separation was carried out in normal polarity mode at 20°C, 30kV and using hydrodynamic injection (50mbar for 1s). The separation was achieved in a bare fused-silica capillary (70cm×75μm i.d.) using a background electrolyte of methyl-β-cyclodextrin (~6mM) and heptakis-(2,3,6-tri-O-methyl)-β-cyclodextrin (~8mM) dissolved in a mixture of Na2HPO4/KH2PO4 (5mM, pH 7.4):ACN:MeOH:n-octanol (3:4:2.5:0.5, v/v/v/v). C4D parameters were set at fixed amplitude of 100V and frequency of 1000kHz. The developed method was validated. Calibration curves of the ten FAs were well correlated (r2>0.99) within the range of 5–250μgmL−1 for lauric acid, and 3–250μgmL−1 for the other FAs. The method was simple and sensitive with detection limits (S/N=3) of 0.9–1.9μgmL−1 and good relative standard deviations of intra- and inter-day for migration times and peak areas (≤9.7%) were achieved. The method was applied to the determination of FAs in margarine samples. The proposed method offers distinct advantages over the GC and HPLC methods, especially in terms of simplicity (without derivatization) and sensitivity.