Characterization of Engineered Nanoparticles Using Centrigugal Field-Flow Fractionation - - Chromatography Online
Characterization of Engineered Nanoparticles Using Centrigugal Field-Flow Fractionation

The Column
Volume 10, Issue 14, pp. 1116

The increased use of nanomaterials in industrial and biomedical applications has led to a rapid growth in nanoparticle production. Concerns have been raised regarding the potential toxic effects of nanoparticles on the environment and human health. Centrifugal field-flow fractionation (CF3) is a technique that can be used to separate and characterize engineered nanoparticles by analysts investigating engineered nanoparticle toxicity. This article demonstrates how CF3 can be performed to separate nanoparticle mixtures based on size, aspect ratio, and density, with high reproducibility and resolution.

Rapid growth in the production and use of nanomaterials for industrial and biomedical applications, as well as consumer products, has raised concerns over the safety of the subsequently released engineered nanoparticles (ENPs) into the environment. To assess the ecotoxicity of ENPs, powerful and sensitive analytical techniques are needed to detect and characterize ENPs in complex environmental matrices. Analyses of broad and complex mixtures can, however, be problematic when bulk characterization techniques, such as dynamic light scattering or electron microscopy, are used.1 Centrifugal field-flow fractionation (CF3) is a mass-based separation technique that fractionates and characterizes nanoparticles and particles of sizes ranging from 7 nm to 30 Ám. Figure 1 shows how particles are separated by their interaction with a centrifugal field. The CF3 channel encircles the centrifuge axis like a belt, and the spinning of the channel generates differential acceleration forces at right angles to the direction of the channel flow. Equilibrium is attained when the field-induced and diffusion-induced migrations of sample components are balanced. Smaller particles, located closer to the channel centre, are swept out faster than the larger particles by the streams of the laminar flow. Particle size (equivalent spherical diameter) can be calculated directly from the retention time using the CF3 theory if the particle density is known:2

Where d is particle equivalent spherical diameter, k is Boltzmann constant, T is temperature in Kelvin, t r is particle retention time, Δρ is the difference in density between the particle and carrier solution, w is channel thickness, G is acceleration, v withdigree is channel flow rate, and v withdigree is channel void volume. Equation 1 shows that in CF3, the retention time is proportional to the cube of the diameter. A twofold increase in the diameter results in an eightfold increase in retention time. The size selectivity (change in retention time per change in size) is three in CF3; that is, three times higher than flow, thermal, or electrical FFF. Hence CF3 is known to be one of the most powerful FFF sub-techniques.3

In this study, CF3 separation of ENPs based on size, aspect ratio, and density is demonstrated. Results for different mixtures of gold and silver nanoparticles will be presented.


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