Application of an Ionic Liquid Column to the Analysis of Flavor and Fragrance Ingredients
Traditional, polar (polyethylene glycol/wax) stationary phase gas chromatography columns pose challenges for flavor and fragrance analysis particularly in regards to thermal instability at high temperatures, degradation when exposed to water, unchanging selectivity, and relatively short shelf lives. Recently, capillary columns using ionic liquids as stationary phases have become available. Ionic liquid columns offer a potential combination of high polarity and high temperature stability with unique selectivity. An in depth discussion about the history and development of column phase characterization, with specific emphasis on selectivity and polarity, will allow for a critical look at the polarity scale currently employed to characterize ionic liquid stationary phases. Performance of an SLB-IL60 column was compared to a traditional HP-20M wax column, with focus on classic thermodynamic parameters – Gibbs free energy, enthalpy, and entropy. This comparison explores retention mechanisms and thermodynamic properties of the ionic liquid stationary phase versus its historical (wax) counterpart. A thorough analysis of these fundamental chemistry parameters developed a strong foundation for a comparison of selectivity and polarity. Ionic liquid columns were found to have similar retention mechanisms for homologous series of primary alcohols and ethyl esters. Thermodynamics revealed differences for homologous series of alkyl aldehydes, alkyl carboxylic acids, and alkanes in regards to retention mechanisms on the SLB-IL60 and HP-20M columns. In addition, a new polyol extraction technique was employed for the extraction of mead (an alcoholic beverage consisting of fermented honey). This extract was compared on both stationary phases to a traditional liquid/liquid extract of the mead. Comparing the activity of flavor and fragrance compounds on ionic liquid and wax stationary phases demonstrated the applicability of ionic liquid columns to the flavor and fragrance industry.
gas chromatography, thermodynamics, flavors, fragrances, ionic liquids, Analytical Chemistry
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