Carbon Nanotubes as a New Solid Phase Extraction Sorbent for Analysis of Environmental Pollutants

Abstract

Pretreatment is often considered to be a fundamental step in the process of successful analysis of environmental pollutants, because it helps not only to achieve low detection limits but also to clean up the sample matrix. Solid phase extraction (SPE) is an effective sample handling method and is used as an enrichment technique when low concentrations of analytes need to be determined. SPE provides higher enrichment efficiency and requires a lower volume of solvent than the traditional method of liquid-liquid extraction. In addition, SPE is simpler and easily to be automated and operated. In the procedure of SPE, the type of sorbent, its structure and its interactions with the solute play an important role in obtaining higher enrichment efficiency of analytes. Until now, several kinds of materials such as C18, Oasis HLB, bonded silica, styrenedivinyl-benzen (SDB), zeolites, carbonaceous materials have been proposed as adsorbents for SPE cartridge. In recent years, carbon nanotubes (CNTs), a novel member in the carbon family, have attracted great attention due to its advantages that can be used for many different applications in terms of its chemical, electronic and mechanical properties as well as the unique tubular structures and large length / diameter ratio. CNTs are to be considered as a sheet of graphite that has been rolled into a tube and be classified as single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs). Over the past 20 years, CNTs have been exploited in analytical and other fields such as biosensors with immobilized biomolecules, electrochemical detectors, gas sensor, catalyst supports and so on. Because CNTs surfaces have a strong interaction with other molecules, particularly with those containing benzene rings, they possess excellent adsorption ability and substitute active carbon. CNTs as SPE adsorbents has been investigated to extract organic compounds such as pesticides (carbofuran, iprobenfos, parathion-methyl, prometryn, fenitrothion etc.), polycyclic aromatic hydrocarbons, antibiotics, sulphonylurea herbicides, sulfonamides, phthalate esters, endocrine disruptors, triazines, microcystines, pyrethroids and polybrominated diphenyl ethers. In several comparative studies CNTs exhibit similar or higher adsorption capacity for environmental pollutants than silica-based sorbents or macroporous resins. CNTs can also preconcentrate volatile organic compounds.CNTs were used as SPE adsorbents for preconcentration of metal ions, such as copper, nichel, cobalt, vanadium, silver, cadmium, rare earth elements etc.