Volume 82, Number 1, April 2008
Article Number 18004
Number of page(s) 6
Section Interdisciplinary Physics and Related Areas of Science and Technology
Published online 17 March 2008
EPL, 82 (2008) 18004
DOI: 10.1209/0295-5075/82/18004

Physical principle for optimizing electrophoretic separation of charged particles

Takeaki Araki and Hajime Tanaka

Institute of Industrial Science, University of Tokyo - Meguro-ku, Tokyo 153-8505, Japan

received 8 August 2007; accepted in final form 12 February 2008; published April 2008
published online 17 March 2008

Electrophoresis is one of the most important methods for separating colloidal particles, carbohydrates, pharmaceuticals, and biological molecules such as DNA, RNA, proteins, in terms of their charge (or size). This method relies on the correlation between the particle drift velocity and the charge (or size). For a high-resolution separation, we need to minimize fluctuations of the drift velocity of particles or molecules. For a high throughput, on the other hand, we need a concentrated solution, in which many-body electrostatic and hydrodynamic interactions may increase velocity fluctuations. Thus, it is crucial to reveal what physical factors destabilize the coherent electrophoretic motion of charged particles. However, this is not an easy task due to complex dynamic couplings between particle motion, hydrodynamic flow, and motion of ion clouds. Here we study this fundamental problem using numerical simulations. We reveal that addition of salt screens both electrostatic and hydrodynamic interactions, but in a different manner. This allows us to minimize the fluctuations of the particle drift velocity for a particular salt concentration. This may have an impact not only on the basic physical understanding of dynamics of driven charged colloids, but also on the optimization of electrophoretic separation.

82.70.Dd - Colloids.
82.45.-h - Electrochemistry and electrophoresis.
83.10.Rs - Computer simulation of molecular and particle dynamics.

© EPLA 2008