Highly sensitive ion preconcentration method based on flow sorbent extraction using multiwall carbon nanotubes

Abstract

In this work a solid phase on-line uranium ion preconcentration system coupled with spectrophotometry has been developed. The method is based on uranyl ion preconcentration at pH 3.75 onto multiwall carbon nanotubes treated with HNO₃. After preconcentration, the uranyl ions are eluted with 0.32 mol L⁻¹HCl followed by reaction with 3,6-bis[(2-arsonophenyl)-azo]-4,5-dihydroxy-2,7-naphthalendisulfonic acid 0.08%[w/v] (Arsenazo III), which had maximum monitored absorbance of 650 nm. Effects of the pertinent experimental parameters on the system were investigated by means of 2⁶⁻² fractional factorial design, while optimization was carried out using the Doehlert matrix. Under optimized conditions, detection and quantification limits were found to be 0.21 and 0.7 µg L⁻¹, respectively. The analytical curve ranged from 5 to 150 µg L⁻¹ (r = 0.998), while the relative standard deviations (RSD) were 3.27 and 2.56% for the respective uranium concentrations of 10 and 100 µg L⁻¹ (n = 10). The features obtained for the on-line preconcentration system were: preconcentration factor of 228, concentration efficiency of 57 min⁻¹, consumption index of 0.13 mL and sample throughput of 15 h⁻¹. In order to assess the accuracy of the proposed method, addition and recovery studies were carried out on spring water samples from different sources and synthetic seawater with satisfactory results ranging from 94.85 up to 103.65%.

Keywords:

• carbon nanotube
• spectrophotometry
• on-line preconcentration
• uranium
• factorial design

Acknowledgements

The authors would like to thank CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico), FAPEMIG (Fundação de Amparo à Pesquisa do Estado de Minas Gerais), CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) and FAPESP (Fundação de Amparo a Pesquisa do Estado de São Paulo) for financial support and fellowships.