An all-solid-state monohydrogen phosphate sensor based on a macrocyclic ionophore

An all-solid-state electrode, containing a synthesized chiral A₂B₂ macrocyclic compound namely (4R,5R,15R,16R)-4,5,15,16-tetraphenyl-3,6,14,17-tetraazatricyclo 13.3.1.18,12] tetracosa-1(23),8,10,12(24)19,21-hexaene-2,7,13,18-tetrone as an ionophore in polyvinyl chloride (PVC)/polyurethane (PU) membrane matrix, has been developed for the selective quantification of monohydrogen phosphate ions. The best performing membrane contained PVC, PU, ionophore, and nitrophenyl octyl ether as a plasticizer in the ratio 32.2:2.6:65.1 (w/w, %). It exhibited a near-Nernstian slope of 31.0 ± 1.0 mV/decade of activity for HPO₄²⁻ ions in the concentration range of 1.0 × 10⁻⁶ to 1.0 × 10⁻² M at pH 7.4. The detection limit of the electrode was 8.4 × 10⁻⁷ M and the life time was six weeks. The electrode displayed excellent selectivity for monohydrogen phosphate over other anions and the selectivity sequence was determined as HPO₄²⁻ > SO₄²⁻ > Ac⁻ > NO₃⁻ > ClO₄⁻ > Cl⁻ > I⁻. The selective electrode for the monohydrogen phosphate ions was evaluated with a standard reference material (SRM 1548) and the titration of the sample solution.