Continuous Millionfold Molecular Concentration Using Pulsed-Field Conductive-Wall Single-Buffer Isotachophoresis

Abstract

We present an experimental study of continuous molecular concentration using plateau and peak model isotachophoresis (ITP). Unlike typical ITP systems which require both a fast-moving leading electrolyte (LE) and slow-moving trailing electrolyte (TE). In a typical ITP experiment, the interface between the TE and LE serves as a concentration zone for ions as their migration outpaces slow moving trailing ions and accumulate at this interface. Physically, the LE can be considered as a no-flux boundary because slower moving sample ions focus and accumulate directly against the edge of an LE zone. In this work we successfully replace this LE with a conductive wall. In this case, the electric field can still penetrate this region due to the wall’s conductivity, but ion migration is impeded due to the physicality of the wall. We perform detailed plateau mode concentration experiments over varying TE ion concentrations and show good agreement with reported peak mode ITP concentration theory. We also demonstrate continuous peak mode ITP concentration and show that our conductive wall ITP can achieve a 4-million-fold concentration factor using only 10 volts DC. Our free-flow wall ITP (FFWITP) offers high concentration power at a fraction of the required voltage without the need of a LE with the increased throughput potential of a continuous process.