AF4 is a system used for the characterisation of nanoparticles, polymers, and proteins (ranging in size from 1nm to 10μm). It is a chromatography-like elution technique with a channel. After a sample injection, a focusing step using a cross-flow generated by the carrier liquid drives all particles to the bottom of a channel. Diffusion of the particles causes them to migrate back into the channel against an applied cross-flow. At equilibrium, these two motions are in balance. Smaller, highly diffusive particles form clouds, which stretch further into the channel than the larger less diffusive particles. Once the focusing step is complete, the focus flow is removed. Different sized particles are held in different regions of the channel as a function of their diffusion coefficient; smaller particles experience higher flow than larger ones and exit the channel first. When coupled to other detectors such as UV-absorbance, fluorescence, light scattering, transmission electron microscopy, atomic force microscopy, inductively coupled plasma mass spectroscopy, AF4 provides information on size, shape, structural parameters, chemical composition and particle-contaminant association of macromolecules and particles in a suspension. It is applicable to carrier solutions with a wide range of pH and ionic strengths, making it possible to match sample composition.
Current activity
- Separate polystyrene nanospheres in environmentally relevant matrices.
- Particle and elemental characterisation of landfill leachates.
- Characterisation of heterogeneous nanoplastics sampled in Solent Water.
Consultancy Work
In addition to carrying out analyses to support research projects across the University of Southampton and through collaborations around the world, we also undertake bespoke analyses on behalf of commercial partners. We have a group of expert scientific and technical staff who are happy to engage in confidential discussions and provide quotes for interested users.
Future Work
We work closely with groups within NOCS, across University the Southampton and from other research organisations. We are always looking to extend our research portfolio and welcome enquiries from potential collaborators, especially those seeking support for post-doctoral fellowships.
Key Contacts