PVC membrane based potentiometric sensors for uranium determination

Abstract

Two novel uranyl PVC matrix membrane sensors responsive to uranyl ion are described. The first sensor incorporates tris(2-ethylhexyl)phosphate (TEHP) as both electroactive material and plasticizer and sodium tetraphenylborate (NaTPB) as an ion discriminator. The sensor displays a rapid and linear response for UO 2 2+ ions over the concentration range 1×10 −1–2×10 −5 mol l −1 UO 2 2+ with a cationic slope of 25.0±0.2 mV decade −1. The working pH range is 2.8–3.6 and the life span is 4 weeks. The second sensor contains O-(1,2-dihydro-2-oxo-1-pyridyl)- N, N, N′, N′-bis(tetra-methylene)uronium hexafluorophosphate (TPTU) as a sensing material, sodium tetraphenylborate as an ion discriminator and dioctyl phenylphosphonate (DOPP) as a plasticizer. Linear and stable response for 1×10 −1–5×10 −5 mol l −1 UO 2 2+ with near-Nernstian slope of 27.5±0.2 mV decade −1 are obtained. The working pH range is 2.5–3.5 and the life span of the sensor is 6 weeks. Interference from many inorganic cations is negligible for both sensors. However, interference caused by some ions (e.g. Th 4+, Cu 2+, Fe 3+) is eliminated by a prior ion exchange or solvent extraction step. Direct potentiometric determination of as little as 5 μg ml −1 uranium in aqueous solutions shows an average recovery of 97.2±1.3%. Application for the determination of uranium at levels of 0.01–1 wt.% in naturally occurring and certified ores gives results with good correlation with data obtained by X-ray fluorescence.