Dispersive micro-solid phase extraction with oxidized carbon nanohorns

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Figure 1. Structure of SWCHs
Carbon allotropes have been extensively used as sorbents in solid phase extraction (SPE) and solid phase microextraction (SPME). Graphitized and activated carbons, fullerenes, carbon nanotubes, diamond and graphene can be highlighted among this class of materials. Today we focus our attention on the potential of carbon nanohorns as sorbent in SPE. Single walled carbon nanohorns (SWCNHs), which were discovered by Ijima in 1999, are single wall graphitic structures formed out of a single graphene sheet rolled up to form conical (horn-like) shapes which are rounded at the tip (1). These nanoparticles, schematically presented in Figure 1, tend to aggregate producing dahlia-like structures with sizes in the range from 80-100 nm. Thanks to their high superficial area and their ability to interact with different analytes, SWCNHs can be considered as promising nanomaterials in extraction procedures (2).

Moreover, the weak interaction between individual SWCNHs in dahlia-like aggregates results in a better dispersibility than the obtained with carbon nanotubes. The application of SWCNHs in dispersive micro-solid phase extraction has been evaluated by researchers from the University of Cordoba at Spain in two recent papers (3,4). In the latter, just accepted for publication in Journal of Chromatography A, the authors evaluate the use of oxidized SWCNHs for the isolation and preconcentration of triazine herbicides from water samples. The oxidation of SWCNHs, which introduces different oxygen-containing functional groups (mainly carboxylic, but also quinone and ether) in the surface of the nanostructures, enhances even further the dispersibility of SWCNHs in water. The oxidation process does not require aggressive reagents since a simple microwave irradiation is enough for this purpose.


In the extraction procedure, 1 mL of an aqueous dispersion of oxidized SWCNHs is sprayed into 10 mL of sample. After 2 min of stirring, the sorbent containing the extracted analytes is recovered by filtration. The final elution, performed with 200 µL of methanol, ensures the preconcentration of the analytes and the compatibility with gas chromatography-mass spectrometry which is selected as instrumental technique. The limits of detection are in the low nanogram per liter range with good precision levels.

In the original article, the readers will find the description of the oxidation process as well as the deep explanation of the optimization and analytical characterization of the proposal.

Refererences
(1) Nanomaterials for Solid State Hydrogen Storage. Springer. Link
(2) Single-walled carbon nanohorn as new solid-phase extraction adsorbent for determination of 4-nitrophenol in water sample. Link
(3) Evaluation of single-walled carbon nanohorns as sorbent in dispersive micro solid-phase extraction. Link
(4) Dispersive micro solid-phase extraction of triazines from waters using oxidized single-walled carbon nanohorns as sorbent. Link

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