Novel Thorium Membrane Sensors with Anionic Response Based on Trioctylphosphine Oxide and Toluate Ionophores
✍ Scribed by Saad S. M. Hassan; Eman M. Elnemma; Amr M. Y. Attawiya
- Publisher
- John Wiley and Sons
- Year
- 2008
- Tongue
- English
- Weight
- 212 KB
- Volume
- 20
- Category
- Article
- ISSN
- 1040-0397
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✦ Synopsis
Two novel potentiometric polymeric membrane sensors for rapid and accurate determination of thorium are described. These are based on the use of trioctylphosphine oxide (TOPO) and thorium toluate (Th-TA) as ionophores dispersed in poly(vinyl chloride) matrix membranes plasticized with nitrophenyloctyl ether. In strong nitric acid medium, Th(IV) nitrate is converted into [Th(NO 3 ) 6 ] 2À complex and sensed as anionic divalent ion which exclude most cationic effect. Validation of the assay methods using the quality assurance standards (linearity range, accuracy, precision, within-day variability, between-day-repeatability, lower detection limit and sensitivity) reveals excellent performance characteristics of both sensors. The sensors exhibit near-Nernstian response for 1.0 Â 10 À6 -1.0 Â 10 À1 M Th over the pH range 2.5 -4.5. Calibration slopes of À 32.3 AE 0.3 and À 27.2 AE 0.2 mV/decade, precision of AE 0.5 and AE 0.8% and accuracy of 98.8 AE 0.9 and 97.9 AE 0.7% are obtained with TOPO and Th-TA based sensors, respectively. Negligible interferences are caused by most interfering mono-, di-, tri-, tetra-, penta-, and hexa-valent elements commonly associated with thorium in naturally occurring minerals and ores. High concentrations of Cl À , F À , SO 4 2À , and NO 3 À ions have no diverse effect. Complete removal of the effect of the interferents in complex matrices is achieved by retention of [Th(NO 3 ) 6 ] 2À complex from 5 M nitric acid/methanol mixture (1 : 9 v/v) on a strong anion exchanger, washing out the cationic interferents followed by stripping off thorium anion complex and measurements. Both sensors are used for determining thorium in certified thorium ore samples (20 -120 mg Th/kg) and some naturally occurring ores (200 -600 mg Th/kg). The results obtained agree fairly well with the certified labeled values or the data obtained using X-ray fluorescence spectrometry