TRANSIENT MODELING OF CAPILLARY ELECTROPHORESIS ISOTACHOPHORESIS

Different algorithms for transient modelling of capillary electrophore sis have been described in several papers. Pro,srams based on such alg orithms were applied to various modes of CE. Surprisingly, simulations of capillary isotachophoresis (cITP) at realistic current densities ( > 1 kA/m(2)) were not reported. Using these programs for practical cIT P conditions resulted in either severe oscillations, mass-balance viol ation or unexpected program termination. This paper addresses several numerical paths available for modelling one-dimensional capillary elec trophoretic behaviour. Tests for determining the validity of the prese nted solutions with respect to cITP were mass balance checks, zone bou ndary thickness and the Kohlrausch regulating function. Six different numerical schemes fulfilled these requirements, yet only few could be used for simulating practical current density situations without causi ng the aforementioned problems. Attention was paid to space discretiza tion (central difference and quadratic upwind) and time integration (i mplicit, explicit). A single computer program comprising these strateg ies was developed. Special features for studying transient state pheno mena were visualization of concentrations, velocities, Peclet and Cour ant numbers, electric field strength, conductivity, pH, buffering capa city and charge excess. All parameters could be displayed in both the space domain (profile) as well as in the time domain (electropherogram ).