Optical chemical sensor of Gd(iii) based on 5-(2'-bromophenyl- azo)-6-hydroxypyrimidine-2,4-dione immobilized on poly(methyl methacrylate) and 2-nitrophenyloctylether matrix.

A novel optical chemical sensor (optode) was fabricated for the determination of Gadolinium ions. The optical sensor was prepared by incorporating a recently synthesized ionophore, 5-(2'-bromophenylazo)-6-hydroxy pyrimidine-2,4-dione (BPAHPD), and 2-nitrophenyloctylether (NPOE) as a plasticizer in poly(methyl methacrylate) (PMMA) membrane. The color of the sensing membrane in contact with Gd(iii) ions changed from yellow to red-orange due to the adsorption of Gd(iii) with the maximum absorbance ( λ max ) at 563 nm. The chemical sensor responds optimally towards Gd(iii) ions at the optimum conditions of pH 7.5, contact time 10 min, 150 ng mL -1 Gd(iii), and 5.0 mL solution. The linear regression equation achieved was A = 4.36C (μg mL -1 ) - 0.15 ( r = 0.9976). A linear Gd(iii) calibration curve can be established in the concentration range of 5.0-250 ng mL -1 with R 2 = 0.9976. Detection and quantification limits are 1.47 and 4.75 ng mL -1 , respectively. The molar absorptivity and Sandell sensitivity are found to be 6.86 × 10 7 L mol -1 cm -1 and 0.023 ng cm -2 , respectively. In addition to its stability and reproducibility, the optode revealed a great selectivity toward Gd(iii) ions as compared to other coexisting ions in real samples. The recovery of Gd(iii) ions from the sensor material was achieved using 0.4 M HNO 3 . The offered optode sensor membrane has been employed to monitor Gd(iii) in soil, sediments, river water, and urine with an internal standard addition method and compared statistically with the ICP-OES method. The results revealed calculated t-values between 1.11-1.85, whereas F values were in the range of 2.46-3.77 which did not exceed the theoretical values, indicating no significant difference at 95% confidence level. The observed percent recovery is in the range of 97.24-102.52%.