This thesis investigates the challenging separation of Pt (IV) from Pd (II) by solvent extraction (SX) using a nonionic hydrophobic deep eutectic solvent of type V (DES) containing trioctylphosphine oxide (TOPO) as a component. Type V DES are highly structured solvents, which are characterized by the presence of an intermolecular hydrogen-bonded network, the strength of which determines their non-ideality and varies with the eutectic composition. The extraction efficiency and selectivity were found to vary widely with the TOPO mole fraction (xTOPO) and the nature of the hydrogen bond donor, which is an antagonism between the SX mechanism and the intermolecular interactions of the DES components. However, the antagonistic effect with increased hydrogen bonding does not influence all extracted species proportionally: While the Pt (IV) extraction remained largely unaffected (% EE ≥ 90%), the extraction of Pd (II) fell sharply, which enabled selectivity to be increased tenfold compared to conventional TOPO-based SX systems. The higher TOPO concentration in DES enabled maximum loading concentrations that were clearly superior to those in organic extractant dilution systems. In addition, the large number of hydrogen-bonded configurations suppresses the formation of a third phase, which limits the traditional SX using nonionic extractants even after extraction of 19.5 gL-1 of Pt (IV) at 8.0 mol. L.-1 HCl in the TOPO + decanoic acid eutectic. The experimental and molecular dynamic simulation results presented here identify the criteria for a rational selection and application of type V DES, which otherwise give poorly selective extraction agents a new life through their inclusion in these systems and at the same time eliminate the need for organic diluents.