Factorial design of electrolyte systems for the separation of fatty acids by capillary electrophoresis

In this work, a capillary zone electrophoretic methodology using UV indirec t detection (224 nm) for the analysis of fatty acids (FAs) in saponified oi ls is proposed. The electrolyte consisted of a 5 mmol l(-1) phosphate buffe r, pH 7, containing 4 mmol l(-1) sodium dodecylbenzenesulfonate (SDBS) as c hromophore, 4 mmol l(-1) dimethyl-beta -cyclodextrin and 45% acetonitrile ( ACN). The composition of the electrolyte was optimized by a 2(3) factorial design with triplicate at the central point. The design established practic al concentration boundaries for SDBS and ACN. In a defined concentration ra nge of 2-4 mmol l(-1), SDBS can certainly be used as a chromophore for indi rect detection without imparting excessive baseline noise. For ACN, a suita ble interval of 45-55% was found to enhance FAs solubilization without over flowing the system with bubble formation and current interruption. Addition ally, the design revealed the importance of dimethyl-beta -cyclodextrin in the resolution of difficult pairs and its function as a solubilizing agent for long chain FAs. At the optimized conditions, nine FAs from C-10 to C-20 , including mono- di- and tri-unsaturated C-18 fatty acids were baseline se parated in less than 10 min. The proposed method was applied to the separat ion of FAs in edible oils and polyunsaturated fatty acid enriched margarine . Additionally, spectral monitoring at 206 nm was used to confirm peak iden tity in the samples. (C) 2001 Elsevier Science B.V. All rights reserved.