SPME as a Tool for Probing Solute Release Mechanisms from Emulsions and Nanostructured Liquids

A solid-phase microextraction (SPME) procedure was evaluated for its application in measuring solute release in the headspace (HS) and in the liquid phase (DI) from emulsified and nanostructured materials. Limonene, a hydrophobic flavor compound present in many foods and beverages, was used as a model solute for evaluating the SPME method. Sampling conditions, including SPME fiber type, sampling times, penetration depths, vial closure materials, and sampling temperatures were evaluated and optimized. By measuring limonene headspace concentrations with different limonene concentrations and different vial sizes, we were able to calculate a vapor-liquid partition coefficient and calculate solute concentrations in both the headspace and the liquid matrix under equilibrium conditions. The calculated partition coefficient (1.7) matched reasonably well to published values (2.0). Based upon these results, we further used the SPME procedures to evaluate solute distributions across the vapor-liquid interface as a function of different liquid matrix properties. The matrices included surfactant micelle solutions and emulsions. For the former, we observed a decrease in the limonene vapor-liquid partition coefficient as a function of increasing micelle concentration. We further observed that different oils used in emulsion formation influenced solute release into the liquid and headspace. These initial results will be used to further study solute transport mechanisms in emulsions, micellar solutions, and other nanostructured materials such as microemulsions.