Luminescence determination of sodium and potassium using molecular sensors on the basis of terbium(III) complexes of 4-carboxybenzocrown ethers

The spectral luminescent properties of terbium(III) complexes of 4-carboxybenzo-15-crown-5 (L1) and 4-carboxybenzo-18-crown-6 (L2) are studied. The quenching of the luminescence of lanthanide by alkali metal ions is discovered, which is referred to as the formation of mixed Tb(III)-L1-Na+ and Tb(III)-L2-K+ complexes. The complexes are useful as molecular sensors for the luminescence determination of Na+ and K+ with the detection limits 1.5 and 25.0 μg/mL. Using the Tb(III)-L1 complex, sodium can be determined in the presence of a 1000-fold excess of potassium. The developed procedures are utilized for the determination of KCl in the Kalipoz medication in tablet form and the total sodium salts (NaCl, NaHCO3) in the Trisol solution for infusions.