Steady-state protein focusing in carrier ampholyte-based isoelectric focusing: Part II-validation and case studies

In this study, we systematically investigate the validity and applicability of an analytical model developed for carrier ampholyte-based isoelectric focusing (IEF). Three different IEF cases are considered in order to evaluate the efficacy of the approximate analytical results by comparison with high-resolution computer simulations. In the first case, three proteins are separated in a narrow pH range (6-9) by using 50 carrier ampholytes. In the second and third cases, the separation of proteins is studied in broad pH range (3-10) IEF by using 100 carrier ampholytes. Results obtained from the approximate analytical models are in very good agreement with the numerical results for IEF separation of cardiac troponin I, albumin, and hemoglobin in both narrow and broad pH ranges. The sensitivity of the analytical model is also tested for different initial mass ratios of proteins to ampholytes. No appreciable differences are observed between the approximate analytical and numerical results within the mass ratio range studied. The effect of a nominal electric field and/or a nominal pH gradient on protein focusing is also examined to demonstrate the effectiveness of the analytical model. Our results indicate that the use of both nominal electric field and pH gradient will result in erroneous peak concentrations for proteins. Finally, we describe the limitations of the approximate analytical solutions.