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.

Abstract

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 (λmax) 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 R2 = 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 × 107 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 HNO3. 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%.