Detection of phosphates in water utilizing a Eu3+-mediated relay mechanism

Abstract

Three carboxamidequinoline ligands were synthesized and their complexes with Eu³⁺ were used for recognition and detection of organic/inorganic phosphates in water. The signal transduction process is based on an “On–Off–On” switch in the fluorescence signal utilizing changes in the intramolecular charge transfer (ICT). The fluorescence emission of ligands is quenched upon exposure to the Eu³⁺ (Off signal). Following the addition of the phosphate analytes the ligand–Eu³⁺ complex disassembles, which results in the regeneration of the original emission of the ligand (On signal). In general, the Eu³⁺ complexes show higher affinity towards adenosine 5′-triphosphate (ATP) and lower affinity to other phosphates, namely adenosine 5′-diphosphate (ADP), adenosine 5′-monophosphate (AMP), pyrophosphate (H₂P₂O₇²⁻, PPi), and dihydrogenphosphate (H₂PO₄⁻, Pi).