Determination of long-chained fatty acids using non-aqueous capillary electrophoresis and indirect UV detection

A method for separation and determination of free saturated long-chained fatty acids (n-C-14-n-C-26) has been developed using non-aqueous capillary electrophoresis with indirect UV detection at 264 nm. The separation medium consisted of 2.5 mM anthraquinone-2-carboxylic acid and 40 mM Tris in N-methylformamide-dioxane (3:1, v/v). The electroosmotic mobility was about 3 . 10(-4) cm(2)/Vs resulting in a separation time of about 15 min. Injection was done at the anode. Sorbic acid and the low mobility anthraquinone-2-sulphonic acid, 2,6-dihydroxy anthraquinone and all-trans-retinoic acid were less suitable as background absorbent. Maximum efficiency (up to 3.2 . 10(5) plates) were obtained in a 54 cm effective length X 50 mu m I.D. capillary at 300 V/cm. However, due to better sensitivity, 75 mu m I.D. capillaries were preferred. Plate numbers of 1.4 . 10(5) were achieved in 75 mu m I.D. capillaries of 46 cm effective length at 300 V/cm. Linear calibration curves were established for the fatty acids n-C-16-n-C-20 (0.025-1.0 mM), n-C-22 (0.025-0.6 mM) and n-C-24-n-C-26 (0.025-0.3 mM) with correlation coefficients better than 0.985, using corrected peak area ratio and n-C-14 fatty acid as internal standard. The concentration limits of detection were about 0.025 mM. The method has been applied for separation of the components in a hydrogenated fish oil, and for separation of dimeric and trimeric acids as well.