Evaluation of an efficient and selective adsorbent based on multi-walled carbon nanotubes coated silica microspheres for detecting nucleobases and nucleosides in human urine

Abstract

Multi-walled carbon nanotubes (MWCNTs) can be used in analytical chemistry for separation and purification and offer the opportunity to determine low concentration compounds in complex systems. Novel multi-walled carbon nanotube coated silica microspheres (MWCNTs/SiO₂) were synthesized by the covalent bonding of amino bonds. The characteristics results obtained from emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and Brunauer–Emmett–Teller (BET) surface area analysis showed that MWCNTs/SiO₂ was successfully prepared. By evaluating the static adsorption capacities of ten nucleobases and nucleosides, the adsorption capacity of the microspheres for adenine (A), guanine (G), uric acid (UA) and xanthosine (X) was found to be significantly stronger than for others. Moreover, the adsorption capacity depends on the pH value, salinity and contact time. It was shown that π–π conjugation and hydrogen bonding interactions were the two main driving forces for the adsorption of target compounds. Adsorption kinetics and adsorption isotherms showed that the adsorption process was a chemical and multilayer adsorption. They could be determined within the test ranges with a good correlation coefficient (r > 0.997). The limits of detection (LOD) for A, G, UA and X were 1.22, 2.02, 0.32 and 2.28 ng mL⁻¹, respectively. The intra- and inter-day relative standard deviations (RSDs) were no more than 6.5%. This procedure therefore afforded a convenient, sensitive and accurate method with a high extraction efficiency for the determination of A, G, UA and X in human urine.