RESUMEN
Reprocessing nuclear-spent fuels is highly demanded for enhanced resource efficacy and removal of the associated radiotoxicity. The present work elucidates the rapid separation of UO2 2+ and Th4+ ions using a reversed-phase high-performance liquid chromatographic (RP-HPLC) technique by dynamically modifying the surface of a C18 silica monolith column with target-specific ionophoric ligands. For the dynamic modification, four analogous aromatic amide ligands, N 1,N 1,N 3,N 3,N 5,N 5-hexa(alkyl)benzene-1,3,5-tricarboxamide (alkyl = butyl, hexyl, octyl, and decyl) as column modifiers were synthesized. The complexation properties and retention profiles of the amide-based column modifiers for the selective and sequential separation of UO2 2+ and Th4+ ions were investigated. In addition, the selective separation of UO2 2+ and Th4+ ions among the competitive ions of similar chemical properties were also studied. The ionophore immobilized C18 silica monolith columns demonstrated a varying degree of retention behavior for UO2 2+ and Th4+ ions (UO2 2+ is retained longer than Th4+ under all analytical conditions), eventually leading to rapid separations within a period of ≤5 min. A 0.1 M solution of 2-hydroxyisobutyric acid (HIBA, 1 mL min-1) served as the mobile phase, and the qualitative and quantitative assessment of the sequentially separated 5f metal ions was achieved through post-column derivatization reaction, using arsenazo(iii) as a post-column reagent (PCR; 1.5 mL min-1) prior to analysis using a UV-vis detector, at 665 nm (λ max). The developed technique was further evaluated by standardizing various analytical parameters, including modifier concentration, mobile phase pH, mobile phase flow rate, etc., to yield the best chromatographic separation. Also, the conceptual role of alkyl chain length (in the modifier) on the retention behavior of the studied metal ions was evaluated for cutting-edge future applications.
RESUMEN
The possibility of a multifunctional and reversible solid-state colorimetric sensor is described for the identification and quantification of ultra-trace Cd2+ and Hg2+ ions, using a honeycomb-structured mesoporous silica monolith conjoined with an indigenous chromoionophoric probe, i.e., 4-hexyl-6-((5-mercapto-1,3,4-thiadiazol-2-yl)diazenyl)benzene-1,3-diol (HMTAR). The amphiphilic probe is characterized using NMR, FT-IR, HR-MS, and CHNS elemental analysis. The structural and surface properties of the monolithic template have been characterized using p-XRD, XPS, TEM-SAED, SEM-EDAX, FT-IR, TG-DTA, and N2 isotherm analysis. The unique structural features and distinct analytical properties of the solid-state sensor proffer a strong response in selectively signaling the target analytes. The probe (HMTAR) exhibits a 1:1 stoichiometric binding ratio with the target ions (Cd2+ & Hg2+), with a visual color change from pale orange to dark red for Cd2+ (525 nm, λmax), and to purple for Hg2+ (530 nm, λmax), respectively, in the pH range 7.0-8.0. The influence of various analytical criteria such as pH, temperature, response kinetics, critical probe concentration, sensor quantity, matrix tolerance, linear response range, reusability, the limit of detection (LOD), and quantification (LOQ) has been investigated to validate the sensor performance. The proposed method displays a linear signal response in the concentration range 5-100 µg/L, with a LOD value of 2.67 and 2.90 µg/L, for Cd2+ and Hg2+, respectively. The real-world efficacy of the sensor material has been tested with real and synthetic water samples with a significant recovery value of ≥ 99.2%, to authenticate its data reliability and reproducibility (RSD ≤ 3.53%). Graphical abstract.