Graphene as coating in solid phase microextraction

Carbon-based nanomaterials have been extensively used as coatings in solid phase microextraction (SPME) due to their outstanding properties such as high thermal and mechanical stability, large superficial area and high affinity towards different compounds. Graphene (G), which was discovered in 2004, consists of one-atom-thick planar sheets of sp²-bonded carbon atoms that are densely packed in a honeycomb crystal lattice (see Figure). It can be considered the building block of some carbon allotropes like carbon nanotubes or graphite. In fact, in the usual synthetic procedure, graphene is obtained in the form of graphene oxide (GO) by chemical exfoliation of graphite. This GO can be finally reduced to G using reagents (like hydrazine or p-phenylene diamine) or a thermal treatment.

Theoretically and according to its structure, G should present a great affinity to aromatic compounds since it is a large delocalized π-electron system that can interact by π- π stacking with benzene rings. In this sense, Chen et al. proposed for the first time the use of G as coating in SPME in 2010 using six pyrethroid pesticides as probes. The fiber coating was prepared by dipping a stainless steel wire (support) into an ethanolic dispersion of G. The physical wrapping was finally reinforced by curing the fiber at high temperature. The coating presented a wrinkled and porous surface, thus enhancing the extraction of the analytes. Moreover, the fiber coating was thermally stable and presented good fiber-to-fiber and batch-to-batch reproducibility. Following a similar process, Wu et al. have recently used a G-coated fiber for the microextraction of herbicides in water samples.

G-based coating can be also obtained by sol-gel technology using GO as starting material. The sol-gel process consists of a controlled polycondensation of different hydroxylated compounds which confers a high thermal and mechanical stability to the coatings. After the polycondensation process, the residual GO is transformed into G by a thermal treatment in order to enhance the non-polar interactions with the targets analytes. Zhang and Lee employed this strategy to prepare a G-based coating to the extraction of polybrominated diphenyl ethers with excellent results.

In all cases, G-based fibers provide better results than their counterparts (PDMS, PA, etc) for the selected analytes.

References

Link to the article: Preparation and evaluation of graphene-coated solid-phase microextraction fiber. Chen et al.

Link to the article: Plunger-in-needle solid-phase microextraction with graphene-based sol–gel coating as sorbent for determination of polybrominated diphenyl ethers. Zhang and Lee.

Link to the article: Graphene coated fiber for solid phase microextraction of triazine herbicides in water samples. Wu et al.