Optimization of a gas chromatographic separation of FAME prepared from dairy products, PHO, and refined vegetable oils applying a negative temperature gradient

Abstract: Analytical methods for the quantification of fatty acids (FA) by gas chrommatography (GC) have continued to evolve since capillary columns were first introduced. Still no single GC method can simultaneously measure all FA, including trans FA (t-FA), that are contained in dairy products, partially hydrogenated oils (PHO), and refined vegetable oils. Using 100% poly(biscyanopropyl siloxane) capillary columns, ruminant and dairy fats are preferentially analyzed by applying temperature programs that separate short chain FA, but not trans-18:3 from 20:1. Refined vegetable oils and PHO are preferentially analyzed by applying isothermal elutions that provide quantification of all 18 carbon t-FA including trans-18:3 FA, but not of all short chain FA. In this presentation, we propose a temperature program method capable of simultaneously measuring short chain FA and all 18 carbon t-FA including trans-18:3 by applying a negative temperature gradient after the elution of trans-18:1. A simplified version of the method is also described for equipment not able to perform negative temperature gradients. This presentation will also discuss the optimization of the GC separations provided by highly polar GC columns to account for small variations in their selectivity caused by column age or usage.