TD-NMR-Based Determination of the Entrapped Water Yield of Water-in-Oil-in-Water Double Emulsions: Influence of Xanthan Gum Addition

Water-in-oil-in-water (W/O/W) double emulsions (DEs) are considered promising systems for encapsulating, protecting, and delivering hydrophilic compounds. However, their thermodynamic instability limits their practical application. The addition of stabilizers and/or thickeners is a straightforward strategy to improve their stability. However, the high viscosity of DEs complicates the accurate determination of their entrapped water yield (EY), especially when applying techniques based on phase separation. In this study, two TD-NMR-based techniques (<i>T</i>₂ relaxometry, and NMR diffusometry) were compared to analytical photocentrifugation to evaluate their effectiveness in determining the entrapped water yield of DEs formulated with various concentrations (0-0.8 wt%) of xanthan gum (Xan) in the external aqueous (W₂) phase. For EY determination, analytical photocentrifugation led to overestimated results for DEs containing xanthan, primarily due to the high viscosity, which inhibited the complete separation between the cream and serum layers. In contrast, after optimizing measurement and analysis conditions to minimize interference from water and/or solute exchange between the inner and outer aqueous phases, <i>T</i>₂ relaxometry and NMR diffusometry yielded comparable EY values for all DEs with or without Xan. Hence, these two TD-NMR-based techniques can be considered direct and reliable methods for EY determination in viscous DE system.