الفهرس 
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Abstract
Herein, we report simple, sensitive, selective and low-cost filter paper strips as uranium(VI) and thorium(IV) optical sensors, wherein different ionophores were incorporated as selective color forming reagents with subsequent measurement of the micellar sensitized color change using a simple desktop scanner as an imaging device. Captured digital images of the filter paper strips carrying the colored complex were cropped and analyzed based on the standard RGB color mode to give RGB intensities that were converted to the corresponding color absorbance values that are directly related to the concentration of U(VI) and Th(IV) in complex certified rock samples. The simplicity, affordability, sensitivity and cost-effectiveness are common features for this approach for the in-situ uranium and thorium analysis.
Morin (2′,3,4′,5,7-Pentahydroxyflavone), was applied as a non-leachable chromogenic reagent for the highly sensitive and selective determination of thorium and uranium. On the other hand, Arsenazo III and 4-(2-Thiazolylazo)-resorcinol (TAR) were also incorporated as chromogenic reagents in the filter paper-based strips that were specially prepared for the assessment of uranium.
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The effects of some surfactants on the spectral characteristics were investigated. The experimental variables and the potential interference of co-existing ions were thoroughly studied. The optimum conditions established were incorporated into respective recommended procedures that were conveniently applied to the determine thorium and uranium in various rock samples including certified reference material rocks.
For Th(IV) determination, filter paper strips (FPOS) impregnated with Morin reagent are reacted with Th(IV) in the presence of cetyltrimethyl ammonium bromide as a surfactant, chloroacetic acid buffer of pH 2.4 at 60 C yielding an intense yellow colored 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 mL-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.
On the other hand, U(VI) determination based on the reaction of U(VI) with Morin reagent, impregnated on filter paper strips, in the presence of hexamine buffer of pH 7.0 at
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25 C yielded a reddish brown colored complex whose color intensity was determined by a desktop scanner. Maximum enhancement of the absorbance of the U-Morin chelate was obtained using cetylpyridinium chloride (CPC). A plot of the blue channel color absorbance versus U(VI) concentration was linear up to 30.0 μg mL-1 with a detection limit of 0.4 μg mL-1. The proposed method was successfully applied to the assessment of U(VI) in complex certified rock samples.
The third filter paper optical sensor (FPOS) for U(VI) assessment based on the reaction of U(VI) with Arsenazo III reagent in the presence of a chloroacetic acid buffer of pH 1.80 at 25 C yielding a green colored complex. Following the optimized conditions of the recommended procedure, the U(VI)-ARZ(III) system obeyed Beer‘s law and a plot of the red channel color absorbance versus U(VI) concentration gave a linear calibration relationship for up to 6.0 μg mL-1 U(VI) with a detection limit of 0.07 μg mL-1.
The fourth proposed method for U(VI) determination using TAR depends on the preparation of a membrane from a mixture of 250.0 μL TAR, 200.0 μL Diethylhexyl phthalate plasticizer, 100.0 μL Trioctylamine, 200.0 μL high M. Wt. Polyvinyl chloride and 250.0 μL CTAB. This cocktail was adopted to avoid the appreciable leaching of TAR into the
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aqueous solutions containing U(VI), when applied alone. A 3.0 μL of the working Cocktail membrane sensor was spotted on a Whatman No. 1 filter paper strip using a micropipette and left to dry in air. Thereafter, the TAR impregnated filter paper strip was dipped in a small beaker containing the equilibrated solution containing uranium. A magenta colored complex formed due to the reaction of uranium with TAR in the presence of acetic acetate buffer solution of pH 5.0 at 25 C. The U(VI)-TAR system obeyed Beer‘s law and a plot of the green channel color absorbance versus U(VI) concentration gave a linear calibration relationship for up to 5.0 μg mL-1 U(VI) and a detection limit of 0.05 μg mL-1 U(VI). The proposed method was successfully applied to the assessment of U(VI) in complex certified rock samples