The structure also affects the solubility in the organic and water solutions used in the liquid/liquid system. Therefore, in the first step the solubility of the compounds in 1 mM BTPPATPBCl salt in DCE and TFT were evaluated. It comes out that 10 out of 19 studied compounds showed sufficient solubility in DCE, while 3 compounds can be solved both in DCE and TFT. The solubility of the tested compounds was assessed visually in small volumes of solution, approximately 1 mL. The first compound tested was (1) -phenylboronic acid -it is a simple boronic acid with a proven affinity for the fluoride anion . It is soluble both in DCE and water. Changes in current versus potential suggested that the phenylboronic acid was transferred across the liquid/liquid interface into the aqueous solution and the fluoride anion bound prior to measurement (Fig. ). It can be supposed that the observed current resulted from boronate ion transfer through the liquid/liquid interface. Compound (15) (10-hydroxy-dibenzoborinine) can attach a fluoride ion, but also exchange one hydroxyl group for a fluoride. Due to the technique used, i.e., ion transfer, it is possible to observe only the process of attaching the fluoride ion to the ionophore molecule because only in this case the charge of the ionophore molecule is changed. Fig. shows the results of fluoride ion transfer at the interface in a liquid/liquid system containing 1 mM (15) solution in the organic phase. An increase in the concentration of fluoride ions in an inorganic solution generates a current peak at a potential of approx. 0.2 V. This peak corresponds to the fluoride ion transfer. Similar results were obtained with the DPV technique. The current peak appears at a potential of 0.2 V and increases as the concentration of fluoride ions in the aqueous phase increases.