Método espectrofotométrico mecanizado de análise "on-line" baseado na pré-concentração de urânio em nanotubo de carbono

Abstract

In this work a solid phase preconcentration system of uranium on-line coupled to spectrophotometry was developed. The method is based on preconcentration of uranium on carbon nanotube oxidized with nitric acid, with further elution with 0.32 mol L-1 hydrochloric acid and reaction with Arsenazo III, being the absorbance of the complex monitored at 650 nm. The screening of the factors relevant to the system was carried out from two level factorial design while the optimization was performed using Doehlert design. The following conditions were optimized: sample pH (3.75), buffer concentration (6.8x10-3 mol L-1), Arsenazo III concentration (0.08% w/v) concentration eluent (0.32 mol L-1), type of eluent (HCl) and preconcentration flow rate (7.2 mL min-1). For the study of interfering held the determination of uranium by means of binary solutions in the following ratios, 1:1; 1:10; 1:100 (m/m) analyte/interferent, respectively. The ions study were: Th4+, Mn2+, Ni2+, Co2+, Cu2+, Fe3+, Cr3+, Cd2+, Zn2+, Pb2+, where the two latter showed interference in the 1:10 proportion. The precision (n=10) was evaluated for the standards 10.0 and 100.0 μg L-1 yielding relative standard deviations of 3.27 and 2.56%, respectively. The method presented preconcentration factor of 228 and respective detection and quantification limits of 0.21 and 0.7 μg L-1. The accuracy of the method was assessed from analysis of water samples from different sources as well as simulated seawater.