BackgroundDeep eutectic solvents have presented excellent properties and have been utilized in various research areas of chemistry. These solvents have recently been reported as one of the most fascinating with promising possibilities when compared to the other solvents. MethodIn this present study, the limiting activity coefficients have been estimated for 32 various volatile organic solutes (aliphatic and aromatic hydrocarbons, alcohols, THF, thiophene, acetonitrile, ketones) and water in [trihexyltetradecylphosphonium decanoate + ethylene glycol] prepared at 1: 4 molar ratio, respectively. Measurements were conducted at different temperatures, T = (313.15–343.15) K and at atmospheric pressure. Gas liquid chromatography coupled with thermal conductivity detector was employed to obtain the experimental retention data of solutes in the deep eutectic solvent. The partial molar excess properties, such as enthalpies, entropies, and Gibbs energies were determined at infinite dilution from the calculated limiting activity coefficients. In addition, the selectivity and capacity values for the separation problems such as (acetone/ethanol, cyclohexane/benzene, benzene/toluene, and butanol/MEK) were determined from the limiting activity coefficients. FindingsThe attained values proved that trihexyltetradecylphosphonium decanoate + ethylene glycol deep eutectic solvent could be utilized in the separation of azeotropes. The results were discussed based on the intermolecular interactions occurring in the deep eutectic solvent mixtures. The influence of the hydrogen bond donor on deep eutectic solvent behavior was discussed.