Filter paper-based optical sensor for the highly sensitive assessment of thorium in rock samples
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Filter paper-based optical sensor for the highly sensitive assessment of thorium in rock samples Ashraf A. Mohamed1 · Islam M. Abd El‑Hay1,2 · Azza F. El Wakil2 · Abd El‑Aziz A. Mohamed2 Received: 20 April 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract Filter paper-based optical sensors (FPOS) offer rapid and sensitive quantification of analytes. Herein we report, a simple, sensitive, selective and low-cost FPOS for Th(IV) determination. Filter paper strips, impregnated with Morin reagent are reacted with Th(IV) yielding an intense yellow complex whose RGB (red/green/blue) color intensities made the basis of the assessment. A plot of the blue channel color absorbance versus Th(IV) concentration was linear up to 4.0 µg m L− 1 with a detection limit of 0.1 µg mL− 1. The proposed method was accurate, precise and reliable for analyzing complex certified rock samples in excellent compliance with the certified values. Keywords Thorium determination · Filter paper-based optical sensor · RGB color absorbance · Certified rock samples
Introduction Thorium is a naturally occurring element that has a number of industrial, medical and nuclear applications and is present in very small quantities in rocks, soil, water and plants. Natural Thorium is usually pure Th232, which is the most stable isotope due to its long half-life [1]. Some instrumental techniques have been reported for the assessment of thorium in real samples based on chemical, physical or radiochemical principles. These include inductively coupled plasma—mass spectrometry (ICP-MS) [2–5], inductively coupled plasma—optical emission spectrometry (ICP-OES) [6–8], neutron activation analysis (NAA) [9–11], ion selective electrodes (ISE’s) [12–14] and spectrophotometry [15–24]. However, the high capital/running/maintenance costs, the well-controlled experimental conditions, the need for laborious separation and enrichment are common disadvantages of many of these methods [25]. On the other hand, methods of digital image-based analysis (DIBA) are suggested as simple and low-cost alternatives for the assessment of trace analytes. DIBA relies on reacting * Ashraf A. Mohamed [email protected] 1
Department of Chemistry, Faculty of Science, Ain Shams University, Abbassia, Cairo 11566, Egypt
Nuclear Materials Authority, P.O. Box 530, El‑Maadi, Cairo, Egypt
2
an analyte with a chromogenic reagent to give a colored product, whose images are captured using a digital camera, a mobile phone camera, a webcam or a scanner. Analysis of these images yielded the RGB (red, green and blue) intensity values (IR, IG, IB and IRGB) and color absorbances (AR, AG, AB and ARGB) as analytical signals for DIBA [26–33]. Herein, we describe a simple, sensitive and low-cost filter paper-based strip as a thorium optical sensor, wherein Morin (3,5,7,2′,4′-pentahydroxy flavone) was incorporated as a color forming reagent with subsequent measurement of the micellar sensitized color change using a simple desktop scanner as an imaging device. The simplicity, afforda
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