Specific Detection Method for Carbon Nanotubes in Complex Matrices

Postnova Analytics has published a new method to characterize and quantify carbon nanotubes in soil samples using Asymmetrical Flow Field-Flow Fractionation coupled with MALS detection (AF4-MALS). Effective methods to characterise and quantify carbon nanotubes from soil samples are rare. Quantification, depending on the method used, may be biased by soot particles commonly found in soils and sediments. Differentiating between carbon nanotubes and soot particles is a big challenge as they are physically and chemically very similar.

Contained with a new application note, the authors of this new method describe their investigation into how particle shape could be used as a contrasting parameter for the detection of carbon nanotubes in pure soot or even soil. In this work the researchers evaluated a shape factor p, derived from AF4-MALS measurements, for its capabilities to detect carbon nanotubes in such complex matrices.

The Postnova AF2000 Multiflow platform employed in this research uses a unique crossflow field design in which samples are separated by their dynamic diffusion on the basis of molar mass or particle size. Because of this design and the absence of any stationary phase, field-flow fractionation on the AF2000 Multiflow can be performed without exerting shear forces and stress on the molecules being separated.

The AF2000 can be run with different eluents, wide ranging temperature conditions and is widely proven to be the perfect system for running AF4 experiments. Consequently the AF2000 Multiflow is an ideal platform for the characterization of nanoparticles in complex matrices.

For determination of the hydrodynamic radius (rh) of the carbon nanotubes in soot and soil samples the researchers used retention time calibration with different certified latex standards. The radius of gyration (rg) was determined using a PN3621 21-angle MALS detector. The application note describes how generation of a shape factor p from rg and rh values over time enables differentiation of carbon nanotubes and soot particles.

Data is shown that demonstrates how shape factor increment is dependent on the ratio between carbon nanotubes and soot in a mixture. The researchers conclude that soil particles extracted by the described method are contrasting to carbon nanotubes in terms of p, allowing specific detection of carbon nanotubes in these complex matrices.