Synthesis of the Au-IEM commenced with the preparation of a casting solution in the form of a 100 % 1.0 L tetrahydrofuran (THF) solution (Merck) containing approximately 20 g of dissolved S5718 PVC (Sasol) and 30 g of undissolved Purogold S992 extractant (Purolite). This casting solution was mixed for 30 min to obtain a uniform distribution of PVC-THF solution and S992 extractant. Once prepared, the casting solution was poured into a 150/15 mm petri dish (sitting on a flat glass plate and covered with filter paper and a watch glass), which was placed in a flat box under inert nitrogen (N2) atmosphere for 24 hrs to allow for THF to evaporate slowly and have little contact with air humidity, thus, to avoid excessive formation of pores (which would result in decreased selectivity and permselectivity of AuI2 -). After complete evaporation of THF, a few droplets of distilled H2O was added into the petri dish, and thereafter the remaining solid (Au-IEM) was peeled off.