Ribonucleic acid as a novel ionophore for potentiometric membrane sensors of some transition metal ions

Abstract

Ribonucleic acid (RNA) is used as a novel ionophore in plasticized poly(vinyl chloride) matrix membrane sensors for some transition metal ions. Membranes incorporating RNA and doped in Cu 2+, Cd 2+ and Fe 2+ display fast near-Nernstian and stable responses for these ions with cationic slopes of 31.1, 31.3 and 35.5 mV per decade, respectively, over the concentration range 10 −6–10 −2 M and pH range 4–6.5. The cadmium RNA-based sensor shows no interference by Cu 2+, Fe 2+ Hg 2+ and Ag +, which are known to interfere significantly with the solid-state CdS/Ag 2S membrane electrode. The copper RNA-based sensor displays general potentiometric characteristics similar to those based on macrocyclic ionophores and organic ion exchangers and has the advantage of a better selectivity for Cu 2+ over some alkaline earth, divalent and transition metal ions. The iron RNA-based membrane sensor exhibits no interference by Hg 2+ and Zn 2+, which are known to interfere with other previously suggested sensors. The nature and composition of the RNA ionophore and its cadmium complex are examined using electrophoresis, Fourier-transform infrared analysis, elemental analysis and X-ray fluorescence techniques.