Influx and Production Rates in Peak-Mode Isotachophoresis

We present an analytical model useful in the design of peak-mode isotachophoresis (ITP) experiments. The model quantifies sample influx and production rates, the latter in applications where ITP is used to accelerate chemical reactions. We include analysis of the effect of initial sample placement location. We derive and identify key nondimensional parameters for the general case of weak electrolyte buffer ions in terms of sample placement (injection mode), initial concentrations, fully ionized mobilities, and reaction kinetic constants. We then discuss how to use these parameters in the optimal design of peak-mode ITP assays and highlight regimes of particular interest. We clearly identify a quasi-equilibrium regime wherein production rates increase until they equal the influx rate of the low abundance sample species. The model and analysis are generally applicable to both cationic and anionic ITP assays and likely to a wide range of sample species.