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ARTICLE IN PRESS

CHROMA-355331; No. of Pages 15

Journal of Chromatography A, xxx (2014) xxx–xxx

Contents lists available at ScienceDirect

Journal of Chromatography A journal homepage: www.elsevier.com/locate/chroma

Review

Carbon-based sorbents: Carbon nanotubes Xiaojing Liang, Shujuan Liu, Shuai Wang, Yong Guo ∗ , Shengxiang Jiang ∗∗ Key Laboratory of Chemistry of Northwestern Plant Resources and Key Laboratory for Natural Medicine of Gansu Province, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, Gansu, China

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Article history: Received 26 February 2014 Received in revised form 11 April 2014 Accepted 11 April 2014 Available online xxx Keywords: Carbon nanotubes Sorbent Solid-phase extraction Solid-phase microextraction

a b s t r a c t Carbon nanotubes (CNTs), as an advanced material, have been widely used in various fields since its discovery in 1991. In recent years, as an excellent adsorption material, the pure and modified CNTs are successfully used for the purification and enrichment of food, medicine, environmental samples and so on. In this review, we focus on the detailed description of different CNTs-based extraction modes such as solid-phase extraction (SPE) (including cartridge and disk SPE, dispersive SPE, and ␮-SPE) and solidphase microextraction (SPME) (including fiber SPME, electrosorption-enhanced SPME, stir bar sorptive extraction, needle trap SPME, and hollow fiber SPME). © 2014 Elsevier B.V. All rights reserved.

Contents 1. 2.

3.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Solid-phase extraction (SPE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Traditional solid-phase extraction (including cartridge and disk SPE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.1. Pure CNTs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.2. Modified CNTs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.3. Molecularly imprinted polymers/CNTs (MIPs/CNTs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Dispersive solid-phase extraction (DSPE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.1. CNTs disaggregation methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.2. CNTs separation methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3. Micro-solid-phase extraction (␮-SPE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1. Coupled with HPLC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2. Coupled with CE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3. Coupled with atomic spectrometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.4. Other online ␮-SPE system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Solid-phase microextraction (SPME) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Fiber solid-phase microextraction (fiber-SPME) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.1. Physical coating method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.2. Sol–gel coating method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.3. Chemical bonding method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.4. Electrophoretic deposition method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2. Electrosorption-enhanced solid-phase microextraction (EE-SPME) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3. Stir bar sorptive extraction (SBSE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4. Needle trap solid-phase microextraction (NT–SPME) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

∗ Corresponding author. Tel.: +86 931 4968274; fax: +86 931 8277088. ∗∗ Corresponding author. Tel.: +86 931 4968266; fax: +86 931 8277088. E-mail addresses: [email protected] (Y. Guo), [email protected] (S. Jiang). http://dx.doi.org/10.1016/j.chroma.2014.04.039 0021-9673/© 2014 Elsevier B.V. All rights reserved.

Please cite this article in press as: X. Liang, et al., J. Chromatogr. A (2014), http://dx.doi.org/10.1016/j.chroma.2014.04.039

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3.5. Hollow fiber solid–liquid phase microextraction (HF-SLPME) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6. Hollow fiber solid-phase microextraction (HF-SPME) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions and future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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1. Introduction

2. Solid-phase extraction (SPE)

Due to the potential adverse effects of trace materials in environment, food, drug, etc. on human being, animal and ecosystem, the analysis of these trace substances in complex matrix samples becomes more and more important in recent years. However, these samples are quite complex and the analytes are in trace amounts, which make the analysis very difficult. So sample pretreatment methods become an important part of the analysis to enrich trace components, to improve the sensitivity of method, as well as to remove interfering substances [1]. SPE is one of the most employed sample preparation methods used for the preconcentration of analytes in different samples due to its advantages of high enrichment factor, high recovery, rapid phase separation, low cost, low consumption of organic solvents and the ability of coupling with different detection techniques in the form of on-line or off-line mode [2,3]. It is well known that method development and selection of the most appropriate sorbent are the two key problems when applying SPE [4]. In regard to appropriate sorbents, various materials have been used such as synthetic resins and its derivatives, carbon, and biological substrates (bacteria, algae or fungus free or immobilized on solid-supports). Since the first report published in 1991 [5], CNTs have been attracted great interest in physics, chemistry, materials scientists and so on. CNTs can be classified as single-walled carbon nanotubes (SWCNTs), which are made of single graphene sheet, having diameters in the range of 1–2 nm, and multi-walled carbon nanotubes (MWCNTs), which are made of several graphene sheets, having diameters ranged from 5 to 50 nm [6,7]. Based on their structure, CNTs show some unique properties, for example, distinctive electrontransport properties, largest elastic modulus, high thermal stability and large available surface area [3]. These unique properties enable CNTs to extend the applicability in scanning probe microscope [8], electrochemical sensor [9], field-effect transistors [10], catalyst [11], hydrogen storage media [12] etc. In this sense, CNTs’ high surface area, ability to establish ␲–␲ interactions, excellent chemical, mechanical and thermal stabilities make them very attractive as SPE materials for either non-polar (in the case of non-functionalized CNTs) and polar compounds (in the case of functionalization CNTs). Up to now, several reviews have been involved in CNTs as SPE sorbents to extract organic and inorganic analytes [4,13–15]. In regard to SPE methods, in recent years, minimizing the use of laboratory solvent and the hazardous waste production, saving the employee labor and time, reducing the cost, and at the same time improving the efficiency of the analyte isolation are the main issues. New developments, for instance, dispersive solid-phase extraction (DSPE), Magnetic solid-phase extraction (MSPE) and solid phase microextraction (SPME) using CNTs as sorbents have been applied for the extraction of many trace analytes from various complex samples. In this review we summarize the various CNTs-based extraction methods for the enrichment of trace analysis (including cartridge, disk and stir bar SPE, DSPE, MSPE, fiber SPME, needle trap SPME, electrosorption-enhanced SPME, hollow fiber SPME, and flow injection online SPME).

Compared to SWCNTs, the MWCNTs composed of several rolledup graphite sheets [16] displays larger specific surface area [17] and higher adsorption capacity [18], which, primarily, is owed to their dramatically hydrophobic surface and unique structure with internal tube cavity [3]. Besides, MWCNTs is much cheaper than SWCNTs. So MWCNTs is more commonly used as the SPE sorbents. Generally, three formats including cartridges, disks, and stir bar are often involved in SPE. 2.1. Traditional solid-phase extraction (including cartridge and disk SPE) The review of Ravelo-Pérez [4], covering articles published since CNTs first being reported up to September 2009, focused on the most important features and different applications of SPE using CNTs especially traditional SPE, we now concentrate on the articles using CNTs as traditional SPE stationary phase since September 2009 up to November 2013. 2.1.1. Pure CNTs In recent years, pure MWCNTs have been successfully used as cartridge SPE sorbents for the extraction of different apolar organic analytes such as PAHs [19], pesticides [20], chemical warfare agents [21], drugs [22,23], parabens [24], thiol compounds [25], auxins [26], dissolved organic matter [27], cobalamins [28], and metal species [29,30]. Most authors employed MWCNTs of narrow diameter (o.d.), mainly of